OOP Intermediate
Polymorphism
Many Forms
Your payment system accepts CreditCard, PayPal, and BankTransfer. Instead of
separate code paths for each, polymorphism lets you treat them all as Payment
objects - calling process() works correctly for each type.
Runtime polymorphism
Parent reference can hold child object.
Runtime.java
Replay: real traced execution (multi-file project)
// Runtime Polymorphism
public class Runtime {
public static void main(String[] args) {
System.out.println("=== Runtime Polymorphism ===\n");
// Same type reference, different objects
Animal a1 = new Dog();
Animal a2 = new Cat();
Animal a3 = new Bird();
// Each calls its OWN version of makeSound()
System.out.println("Calling makeSound() on each:");
a1.makeSound(); // Woof!
a2.makeSound(); // Meow!
a3.makeSound(); // Tweet!
System.out.println("\n=== Why 'Polymorphism'? ===");
System.out.println("""
Poly = Many
Morph = Forms
Same method name (makeSound)
Many different behaviors (woof, meow, tweet)
""");
System.out.println("=== Method Called at Runtime ===");
// The actual method called depends on the OBJECT
int choice = 0;
Animal mystery = getAnimal(choice);
System.out.println("Mystery animal says:");
mystery.makeSound(); // Which version? Depends on actual object!
}
static Animal getAnimal(int choice) {
return switch(choice) {
case 0 -> new Dog();
case 1 -> new Cat();
default -> new Bird();
};
}
}
class Animal {
void makeSound() {
System.out.println("Some generic sound");
}
}
class Dog extends Animal {
@Override
void makeSound() {
System.out.println("Woof! Woof!");
}
}
class Cat extends Animal {
@Override
void makeSound() {
System.out.println("Meow!");
}
}
class Bird extends Animal {
@Override
void makeSound() {
System.out.println("Tweet! Tweet!");
}
}
// Runtime Polymorphism
public class Runtime {
public static void main(String[] args) {
System.out.println("=== Runtime Polymorphism ===\n");
// Same type reference, different objects
Animal a1 = new Dog();
Animal a2 = new Cat();
Animal a3 = new Bird();
// Each calls its OWN version of makeSound()
System.out.println("Calling makeSound() on each:");
a1.makeSound(); // Woof!
a2.makeSound(); // Meow!
a3.makeSound(); // Tweet!
System.out.println("\n=== Why 'Polymorphism'? ===");
System.out.println("""
Poly = Many
Morph = Forms
Same method name (makeSound)
Many different behaviors (woof, meow, tweet)
""");
System.out.println("=== Method Called at Runtime ===");
// The actual method called depends on the OBJECT
int choice = 1;
Animal mystery = getAnimal(choice);
System.out.println("Mystery animal says:");
mystery.makeSound(); // Which version? Depends on actual object!
}
static Animal getAnimal(int choice) {
return switch(choice) {
case 0 -> new Dog();
case 1 -> new Cat();
default -> new Bird();
};
}
}
class Animal {
void makeSound() {
System.out.println("Some generic sound");
}
}
class Dog extends Animal {
@Override
void makeSound() {
System.out.println("Woof! Woof!");
}
}
class Cat extends Animal {
@Override
void makeSound() {
System.out.println("Meow!");
}
}
class Bird extends Animal {
@Override
void makeSound() {
System.out.println("Tweet! Tweet!");
}
}
// Runtime Polymorphism
public class Runtime {
public static void main(String[] args) {
System.out.println("=== Runtime Polymorphism ===\n");
// Same type reference, different objects
Animal a1 = new Dog();
Animal a2 = new Cat();
Animal a3 = new Bird();
// Each calls its OWN version of makeSound()
System.out.println("Calling makeSound() on each:");
a1.makeSound(); // Woof!
a2.makeSound(); // Meow!
a3.makeSound(); // Tweet!
System.out.println("\n=== Why 'Polymorphism'? ===");
System.out.println("""
Poly = Many
Morph = Forms
Same method name (makeSound)
Many different behaviors (woof, meow, tweet)
""");
System.out.println("=== Method Called at Runtime ===");
// The actual method called depends on the OBJECT
int choice = 2;
Animal mystery = getAnimal(choice);
System.out.println("Mystery animal says:");
mystery.makeSound(); // Which version? Depends on actual object!
}
static Animal getAnimal(int choice) {
return switch(choice) {
case 0 -> new Dog();
case 1 -> new Cat();
default -> new Bird();
};
}
}
class Animal {
void makeSound() {
System.out.println("Some generic sound");
}
}
class Dog extends Animal {
@Override
void makeSound() {
System.out.println("Woof! Woof!");
}
}
class Cat extends Animal {
@Override
void makeSound() {
System.out.println("Meow!");
}
}
class Bird extends Animal {
@Override
void makeSound() {
System.out.println("Tweet! Tweet!");
}
}
a1 ← ⟨Dog A⟩, a2 ← ⟨Cat B⟩, a3 ← ⟨Bird C⟩
3public class Runtime {4 public static void main(String[] args) {5 System.out.println("=== Runtime Polymorphism ===\n");6 7 // Same type reference, different objects //?sameref8 Animal a1→ ⟨Dog A⟩ = new Dog(); //?dogasanimal9 Animal a2→ ⟨Cat B⟩ = new Cat(); //?catasanimal10 Animal a3→ ⟨Bird C⟩ = new Bird();11 12 // Each calls its OWN version of makeSound() //?owncall13 System.out.println("Calling makeSound() on each:");14 a1.makeSound(); // Woof!15 a2.makeSound(); // Meow!output=== Runtime Polymorphism === Calling makeSound() on each:@Override void makeSound()
pass 1 of 213 System.out.println("Calling makeSound() on each:");14 a1.makeSound(); // Woof!15 a2.makeSound(); // Meow!16 a3.makeSound(); // Tweet!17 18 System.out.println("\n=== Why 'Polymorphism'? ===");19 System.out.println("""20 Poly = Many21 Morph = Forms22 23 Same method name (makeSound)24 Many different behaviors (woof, meow, tweet)25 """);26 27 System.out.println("=== Method Called at Runtime ===");28 29 // The actual method called depends on the OBJECT //?runtime30 int choice = 0; //@choice=1, 231 Animal mystery = getAnimal(choice);32 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object! //?mystery34 }35 36 static Animal getAnimal(int choice) { //?factory37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42 }43}4445class Animal {46 void makeSound() {47 System.out.println("Some generic sound");48 }49}5051class Dog extends Animal {52 @Override53 void makeSound() { //?dogoverride54 System.out.println("Woof! Woof!");55 }outputWoof! Woof!@Override void makeSound()
14 a1.makeSound(); // Woof!15 a2.makeSound(); // Meow!16 a3.makeSound(); // Tweet!17 18 System.out.println("\n=== Why 'Polymorphism'? ===");19 System.out.println("""20 Poly = Many21 Morph = Forms22 23 Same method name (makeSound)24 Many different behaviors (woof, meow, tweet)25 """);26 27 System.out.println("=== Method Called at Runtime ===");28 29 // The actual method called depends on the OBJECT //?runtime30 int choice = 0; //@choice=1, 231 Animal mystery = getAnimal(choice);32 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object! //?mystery34 }35 36 static Animal getAnimal(int choice) { //?factory37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42 }43}4445class Animal {46 void makeSound() {47 System.out.println("Some generic sound");48 }49}5051class Dog extends Animal {52 @Override53 void makeSound() { //?dogoverride54 System.out.println("Woof! Woof!");55 }56}5758class Cat extends Animal {59 @Override60 void makeSound() { //?catoverride61 System.out.println("Meow!");62 }outputMeow!choice ← 0
15 a2.makeSound(); // Meow!16 a3.makeSound(); // Tweet!17 18 System.out.println("\n=== Why 'Polymorphism'? ===");19 System.out.println("""20 Poly = Many21 Morph = Forms22 23 Same method name (makeSound)24 Many different behaviors (woof, meow, tweet)25 """);26 27 System.out.println("=== Method Called at Runtime ===");28 29 // The actual method called depends on the OBJECT //?runtime30 int choice→ 0 = 0; //@choice=1, 231 Animal mystery = getAnimal(choice0);32 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object! //?mystery34 }35 36 static Animal getAnimal(int choice) { //?factory37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42 }43}4445class Animal {46 void makeSound() {47 System.out.println("Some generic sound");48 }49}5051class Dog extends Animal {52 @Override53 void makeSound() { //?dogoverride54 System.out.println("Woof! Woof!");55 }56}5758class Cat extends Animal {59 @Override60 void makeSound() { //?catoverride61 System.out.println("Meow!");62 }63}6465class Bird extends Animal {66 @Override67 void makeSound() {68 System.out.println("Tweet! Tweet!");69 }outputTweet! Tweet! === Why 'Polymorphism'? === Poly = Many Morph = Forms Same method name (makeSound) Many different behaviors (woof, meow, tweet) === Method Called at Runtime ===static Animal getAnimal(int choice)
36static Animal getAnimal(int choice0) { //?factory37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42}mystery ← ⟨Dog D⟩
30 int choice = 0; //@choice=1, 231 Animal mystery→ ⟨Dog D⟩ = getAnimal(choice0);32 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object! //?mystery34}outputMystery animal says:@Override void makeSound()
pass 2 of 232 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object! //?mystery34 }35 36 static Animal getAnimal(int choice) { //?factory37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42 }43}4445class Animal {46 void makeSound() {47 System.out.println("Some generic sound");48 }49}5051class Dog extends Animal {52 @Override53 void makeSound() { //?dogoverride54 System.out.println("Woof! Woof!");55 }outputWoof! Woof!
a1 ← ⟨Dog A⟩, a2 ← ⟨Cat B⟩, a3 ← ⟨Bird C⟩
3public class Runtime {4 public static void main(String[] args) {5 System.out.println("=== Runtime Polymorphism ===\n");6 7 // Same type reference, different objects8 Animal a1→ ⟨Dog A⟩ = new Dog();9 Animal a2→ ⟨Cat B⟩ = new Cat();10 Animal a3→ ⟨Bird C⟩ = new Bird();11 12 // Each calls its OWN version of makeSound()13 System.out.println("Calling makeSound() on each:");14 a1.makeSound(); // Woof!15 a2.makeSound(); // Meow!output=== Runtime Polymorphism === Calling makeSound() on each:@Override void makeSound()
13 System.out.println("Calling makeSound() on each:");14 a1.makeSound(); // Woof!15 a2.makeSound(); // Meow!16 a3.makeSound(); // Tweet!17 18 System.out.println("\n=== Why 'Polymorphism'? ===");19 System.out.println("""20 Poly = Many21 Morph = Forms22 23 Same method name (makeSound)24 Many different behaviors (woof, meow, tweet)25 """);26 27 System.out.println("=== Method Called at Runtime ===");28 29 // The actual method called depends on the OBJECT30 int choice = 1;31 Animal mystery = getAnimal(choice);32 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object!34 }35 36 static Animal getAnimal(int choice) {37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42 }43}4445class Animal {46 void makeSound() {47 System.out.println("Some generic sound");48 }49}5051class Dog extends Animal {52 @Override53 void makeSound() {54 System.out.println("Woof! Woof!");55 }outputWoof! Woof!@Override void makeSound()
pass 1 of 214 a1.makeSound(); // Woof!15 a2.makeSound(); // Meow!16 a3.makeSound(); // Tweet!17 18 System.out.println("\n=== Why 'Polymorphism'? ===");19 System.out.println("""20 Poly = Many21 Morph = Forms22 23 Same method name (makeSound)24 Many different behaviors (woof, meow, tweet)25 """);26 27 System.out.println("=== Method Called at Runtime ===");28 29 // The actual method called depends on the OBJECT30 int choice = 1;31 Animal mystery = getAnimal(choice);32 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object!34 }35 36 static Animal getAnimal(int choice) {37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42 }43}4445class Animal {46 void makeSound() {47 System.out.println("Some generic sound");48 }49}5051class Dog extends Animal {52 @Override53 void makeSound() {54 System.out.println("Woof! Woof!");55 }56}5758class Cat extends Animal {59 @Override60 void makeSound() {61 System.out.println("Meow!");62 }outputMeow!choice ← 1
15 a2.makeSound(); // Meow!16 a3.makeSound(); // Tweet!17 18 System.out.println("\n=== Why 'Polymorphism'? ===");19 System.out.println("""20 Poly = Many21 Morph = Forms22 23 Same method name (makeSound)24 Many different behaviors (woof, meow, tweet)25 """);26 27 System.out.println("=== Method Called at Runtime ===");28 29 // The actual method called depends on the OBJECT30 int choice→ 1 = 1;31 Animal mystery = getAnimal(choice1);32 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object!34 }35 36 static Animal getAnimal(int choice) {37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42 }43}4445class Animal {46 void makeSound() {47 System.out.println("Some generic sound");48 }49}5051class Dog extends Animal {52 @Override53 void makeSound() {54 System.out.println("Woof! Woof!");55 }56}5758class Cat extends Animal {59 @Override60 void makeSound() {61 System.out.println("Meow!");62 }63}6465class Bird extends Animal {66 @Override67 void makeSound() {68 System.out.println("Tweet! Tweet!");69 }outputTweet! Tweet! === Why 'Polymorphism'? === Poly = Many Morph = Forms Same method name (makeSound) Many different behaviors (woof, meow, tweet) === Method Called at Runtime ===static Animal getAnimal(int choice)
36static Animal getAnimal(int choice1) {37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42}mystery ← ⟨Cat D⟩
30 int choice = 1;31 Animal mystery→ ⟨Cat D⟩ = getAnimal(choice1);32 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object!34}outputMystery animal says:@Override void makeSound()
pass 2 of 232 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object!34 }35 36 static Animal getAnimal(int choice) {37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42 }43}4445class Animal {46 void makeSound() {47 System.out.println("Some generic sound");48 }49}5051class Dog extends Animal {52 @Override53 void makeSound() {54 System.out.println("Woof! Woof!");55 }56}5758class Cat extends Animal {59 @Override60 void makeSound() {61 System.out.println("Meow!");62 }outputMeow!
a1 ← ⟨Dog A⟩, a2 ← ⟨Cat B⟩, a3 ← ⟨Bird C⟩
3public class Runtime {4 public static void main(String[] args) {5 System.out.println("=== Runtime Polymorphism ===\n");6 7 // Same type reference, different objects8 Animal a1→ ⟨Dog A⟩ = new Dog();9 Animal a2→ ⟨Cat B⟩ = new Cat();10 Animal a3→ ⟨Bird C⟩ = new Bird();11 12 // Each calls its OWN version of makeSound()13 System.out.println("Calling makeSound() on each:");14 a1.makeSound(); // Woof!15 a2.makeSound(); // Meow!output=== Runtime Polymorphism === Calling makeSound() on each:@Override void makeSound()
13 System.out.println("Calling makeSound() on each:");14 a1.makeSound(); // Woof!15 a2.makeSound(); // Meow!16 a3.makeSound(); // Tweet!17 18 System.out.println("\n=== Why 'Polymorphism'? ===");19 System.out.println("""20 Poly = Many21 Morph = Forms22 23 Same method name (makeSound)24 Many different behaviors (woof, meow, tweet)25 """);26 27 System.out.println("=== Method Called at Runtime ===");28 29 // The actual method called depends on the OBJECT30 int choice = 2;31 Animal mystery = getAnimal(choice);32 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object!34 }35 36 static Animal getAnimal(int choice) {37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42 }43}4445class Animal {46 void makeSound() {47 System.out.println("Some generic sound");48 }49}5051class Dog extends Animal {52 @Override53 void makeSound() {54 System.out.println("Woof! Woof!");55 }outputWoof! Woof!@Override void makeSound()
14 a1.makeSound(); // Woof!15 a2.makeSound(); // Meow!16 a3.makeSound(); // Tweet!17 18 System.out.println("\n=== Why 'Polymorphism'? ===");19 System.out.println("""20 Poly = Many21 Morph = Forms22 23 Same method name (makeSound)24 Many different behaviors (woof, meow, tweet)25 """);26 27 System.out.println("=== Method Called at Runtime ===");28 29 // The actual method called depends on the OBJECT30 int choice = 2;31 Animal mystery = getAnimal(choice);32 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object!34 }35 36 static Animal getAnimal(int choice) {37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42 }43}4445class Animal {46 void makeSound() {47 System.out.println("Some generic sound");48 }49}5051class Dog extends Animal {52 @Override53 void makeSound() {54 System.out.println("Woof! Woof!");55 }56}5758class Cat extends Animal {59 @Override60 void makeSound() {61 System.out.println("Meow!");62 }outputMeow!choice ← 2
pass 1 of 215 a2.makeSound(); // Meow!16 a3.makeSound(); // Tweet!17 18 System.out.println("\n=== Why 'Polymorphism'? ===");19 System.out.println("""20 Poly = Many21 Morph = Forms22 23 Same method name (makeSound)24 Many different behaviors (woof, meow, tweet)25 """);26 27 System.out.println("=== Method Called at Runtime ===");28 29 // The actual method called depends on the OBJECT30 int choice→ 2 = 2;31 Animal mystery = getAnimal(choice2);32 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object!34 }35 36 static Animal getAnimal(int choice) {37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42 }43}4445class Animal {46 void makeSound() {47 System.out.println("Some generic sound");48 }49}5051class Dog extends Animal {52 @Override53 void makeSound() {54 System.out.println("Woof! Woof!");55 }56}5758class Cat extends Animal {59 @Override60 void makeSound() {61 System.out.println("Meow!");62 }63}6465class Bird extends Animal {66 @Override67 void makeSound() {68 System.out.println("Tweet! Tweet!");69 }outputTweet! Tweet! === Why 'Polymorphism'? === Poly = Many Morph = Forms Same method name (makeSound) Many different behaviors (woof, meow, tweet) === Method Called at Runtime ===static Animal getAnimal(int choice)
36static Animal getAnimal(int choice2) {37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42}mystery ← ⟨Bird D⟩
30 int choice = 2;31 Animal mystery→ ⟨Bird D⟩ = getAnimal(choice2);32 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object!34}outputMystery animal says:@Override void makeSound()
pass 2 of 232 System.out.println("Mystery animal says:");33 mystery.makeSound(); // Which version? Depends on actual object!34 }35 36 static Animal getAnimal(int choice) {37 return switch(choice) {38 case 0 -> new Dog();39 case 1 -> new Cat();40 default -> new Bird();41 };42 }43}4445class Animal {46 void makeSound() {47 System.out.println("Some generic sound");48 }49}5051class Dog extends Animal {52 @Override53 void makeSound() {54 System.out.println("Woof! Woof!");55 }56}5758class Cat extends Animal {59 @Override60 void makeSound() {61 System.out.println("Meow!");62 }63}6465class Bird extends Animal {66 @Override67 void makeSound() {68 System.out.println("Tweet! Tweet!");69 }outputTweet! Tweet!
Animal a = new Dog() - variable type is Animal, object is Dog.
polymorphism
Same code works with different types. Parent reference, child behavior.
Parent reference to child
Store different subtypes in parent-type variable.
ParentReference.java
Replay: real traced execution (multi-file project)
// Using Parent Type to Reference Child Objects
public class ParentReference {
public static void main(String[] args) {
System.out.println("=== Parent Reference, Child Object ===\n");
// Different declaration styles
Dog dog = new Dog("Buddy");
Animal animal = new Dog("Max");
// Both work for inherited methods
System.out.println("Both can make sounds:");
dog.makeSound();
animal.makeSound();
System.out.println("\n=== Access Differences ===");
// Dog reference: full access
dog.makeSound(); // OK - inherited
dog.fetch(); // OK - Dog-specific
// Animal reference: limited access
animal.makeSound(); // OK - defined in Animal
// animal.fetch(); // ERROR! Animal doesn't know about fetch
System.out.println("\n=== Why Use Parent Reference? ===");
// Flexibility: accept any animal
feedAnimal(new Dog("Rex"));
feedAnimal(new Cat("Whiskers"));
System.out.println("\n=== Upcasting (Automatic) ===");
Dog rex = new Dog("Rex");
Animal asAnimal = rex;
System.out.println("Upcasted: Dog → Animal");
System.out.println("\n=== Downcasting (Manual) ===");
Animal mystery = new Dog("Scout");
Dog backToDog = (Dog) mystery;
backToDog.fetch(); // Now we can call fetch!
System.out.println("Downcasted: Animal → Dog");
}
// Method accepts ANY Animal
static void feedAnimal(Animal a) {
System.out.println("Feeding the animal...");
a.makeSound(); // Works for any animal type
}
}
class Animal {
String name;
Animal(String name) {
this.name = name;
}
void makeSound() {
System.out.println(name + " makes a sound");
}
}
class Dog extends Animal {
Dog(String name) {
super(name);
}
@Override
void makeSound() {
System.out.println(name + " barks: Woof!");
}
void fetch() {
System.out.println(name + " fetches the ball!");
}
}
class Cat extends Animal {
Cat(String name) {
super(name);
}
@Override
void makeSound() {
System.out.println(name + " meows: Meow!");
}
}
public static void main(String[] args)
3public class ParentReference {4 public static void main(String[] args) {5 System.out.println("=== Parent Reference, Child Object ===\n");6 7 // Different declaration styles //?styles8 Dog dog = new Dog("Buddy"); //?dogref9 Animal animal = new Dog("Max"); //?animalrefoutput=== Parent Reference, Child Object ===this.name ← Buddy
pass 1 of 656Animal(String nameBuddy) {57 this.name→ Buddy = nameBuddy;58}All 6 passes — pass 1 is the card above pass nameathis.name1 Buddy — Buddy 2 Max — Max 3 Rex ⟨Dog A⟩ Rex 4 Whiskers ⟨Cat B⟩ Whiskers 5 Rex — Rex 6 Scout — Scout dog ← ⟨Dog C⟩
pass 1 of 57 // Different declaration styles //?styles8 Dog dog→ ⟨Dog C⟩ = new Dog("Buddy"); //?dogref9 Animal animal = new Dog("Max"); //?animalref10 11 // Both work for inherited methods12 System.out.println("Both can make sounds:");13 dog.makeSound();14 animal.makeSound();15 16 System.out.println("\n=== Access Differences ===");17 18 // Dog reference: full access //?fullaccess19 dog.makeSound(); // OK - inherited20 dog.fetch(); // OK - Dog-specific21 22 // Animal reference: limited access //?limited23 animal.makeSound(); // OK - defined in Animal24 // animal.fetch(); // ERROR! Animal doesn't know about fetch //?nofetch25 26 System.out.println("\n=== Why Use Parent Reference? ===");27 28 // Flexibility: accept any animal //?flexibility29 feedAnimal(new Dog("Rex"));30 feedAnimal(new Cat("Whiskers"));31 32 System.out.println("\n=== Upcasting (Automatic) ===");33 34 Dog rex = new Dog("Rex");35 Animal asAnimal = rex; //?upcast36 System.out.println("Upcasted: Dog → Animal");37 38 System.out.println("\n=== Downcasting (Manual) ===");39 40 Animal mystery = new Dog("Scout");41 Dog backToDog = (Dog) mystery; //?downcast42 backToDog.fetch(); // Now we can call fetch!43 System.out.println("Downcasted: Animal → Dog");44 }45 46 // Method accepts ANY Animal //?acceptany47 static void feedAnimal(Animal a) {48 System.out.println("Feeding the animal...");49 a.makeSound(); // Works for any animal type50 }51}5253class Animal {54 String name;55 56 Animal(String name) {57 this.name = name;58 }59 60 void makeSound() {61 System.out.println(name + " makes a sound");62 }63}6465class Dog extends Animal {66 Dog(String nameBuddy) {67 super(name);All 5 passes — pass 1 is the card above pass nameadoganimalrexasAnimalmysterybackToDog1 Buddy — ⟨Dog C⟩ — — — — — 2 Max — — ⟨Dog D⟩ — — — — 3 Rex ⟨Dog A⟩ — — — — — — 4 Rex — — — ⟨Dog E⟩ ⟨Dog E⟩ — — 5 Scout — — — — — ⟨Dog F⟩ ⟨Dog F⟩ @Override void makeSound()
pass 1 of 512 System.out.println("Both can make sounds:");13 dog.makeSound();14 animal.makeSound();15 16 System.out.println("\n=== Access Differences ===");17 18 // Dog reference: full access //?fullaccess19 dog.makeSound(); // OK - inherited20 dog.fetch(); // OK - Dog-specific21 22 // Animal reference: limited access //?limited23 animal.makeSound(); // OK - defined in Animal24 // animal.fetch(); // ERROR! Animal doesn't know about fetch //?nofetch25 26 System.out.println("\n=== Why Use Parent Reference? ===");27 28 // Flexibility: accept any animal //?flexibility29 feedAnimal(new Dog("Rex"));30 feedAnimal(new Cat("Whiskers"));31 32 System.out.println("\n=== Upcasting (Automatic) ===");33 34 Dog rex = new Dog("Rex");35 Animal asAnimal = rex; //?upcast36 System.out.println("Upcasted: Dog → Animal");37 38 System.out.println("\n=== Downcasting (Manual) ===");39 40 Animal mystery = new Dog("Scout");41 Dog backToDog = (Dog) mystery; //?downcast42 backToDog.fetch(); // Now we can call fetch!43 System.out.println("Downcasted: Animal → Dog");44 }45 46 // Method accepts ANY Animal //?acceptany47 static void feedAnimal(Animal a) {48 System.out.println("Feeding the animal...");49 a.makeSound(); // Works for any animal type50 }51}5253class Animal {54 String name;55 56 Animal(String name) {57 this.name = name;58 }59 60 void makeSound() {61 System.out.println(name + " makes a sound");62 }63}6465class Dog extends Animal {66 Dog(String name) {67 super(name);68 }69 70 @Override71 void makeSound() {72 System.out.println(nameBuddy + " barks: Woof!");73 }outputBuddy barks: Woof!All 5 passes — pass 1 is the card above pass namea1 Buddy — 2 Max — 3 Buddy — 4 Max ⟨Dog A⟩ 5 Rex ⟨Cat B⟩ void fetch()
pass 1 of 219 dog.makeSound(); // OK - inherited20 dog.fetch(); // OK - Dog-specific21 22 // Animal reference: limited access //?limited23 animal.makeSound(); // OK - defined in Animal24 // animal.fetch(); // ERROR! Animal doesn't know about fetch //?nofetch25 26 System.out.println("\n=== Why Use Parent Reference? ===");27 28 // Flexibility: accept any animal //?flexibility29 feedAnimal(new Dog("Rex"));30 feedAnimal(new Cat("Whiskers"));31 32 System.out.println("\n=== Upcasting (Automatic) ===");33 34 Dog rex = new Dog("Rex");35 Animal asAnimal = rex; //?upcast36 System.out.println("Upcasted: Dog → Animal");37 38 System.out.println("\n=== Downcasting (Manual) ===");39 40 Animal mystery = new Dog("Scout");41 Dog backToDog = (Dog) mystery; //?downcast42 backToDog.fetch(); // Now we can call fetch!43 System.out.println("Downcasted: Animal → Dog");44 }45 46 // Method accepts ANY Animal //?acceptany47 static void feedAnimal(Animal a) {48 System.out.println("Feeding the animal...");49 a.makeSound(); // Works for any animal type50 }51}5253class Animal {54 String name;55 56 Animal(String name) {57 this.name = name;58 }59 60 void makeSound() {61 System.out.println(name + " makes a sound");62 }63}6465class Dog extends Animal {66 Dog(String name) {67 super(name);68 }69 70 @Override71 void makeSound() {72 System.out.println(name + " barks: Woof!");73 }74 75 void fetch() { //?fetchmethod76 System.out.println(nameBuddy + " fetches the ball!");77 }outputBuddy fetches the ball!static void feedAnimal(Animal a)
pass 1 of 246// Method accepts ANY Animal //?acceptany47static void feedAnimal(Animal a⟨Dog A⟩) {48 System.out.println("Feeding the animal...");49 a.makeSound(); // Works for any animal type50}outputFeeding the animal...Cat(String name)
80class Cat extends Animal {81 Cat(String nameWhiskers) {82 super(name);static void feedAnimal(Animal a)
pass 2 of 246// Method accepts ANY Animal //?acceptany47static void feedAnimal(Animal a⟨Cat B⟩) {48 System.out.println("Feeding the animal...");49 a.makeSound(); // Works for any animal type50}outputFeeding the animal...@Override void makeSound()
29 feedAnimal(new Dog("Rex"));30 feedAnimal(new Cat("Whiskers"));31 32 System.out.println("\n=== Upcasting (Automatic) ===");33 34 Dog rex = new Dog("Rex");35 Animal asAnimal = rex; //?upcast36 System.out.println("Upcasted: Dog → Animal");37 38 System.out.println("\n=== Downcasting (Manual) ===");39 40 Animal mystery = new Dog("Scout");41 Dog backToDog = (Dog) mystery; //?downcast42 backToDog.fetch(); // Now we can call fetch!43 System.out.println("Downcasted: Animal → Dog");44 }45 46 // Method accepts ANY Animal //?acceptany47 static void feedAnimal(Animal a) {48 System.out.println("Feeding the animal...");49 a.makeSound(); // Works for any animal type50 }51}5253class Animal {54 String name;55 56 Animal(String name) {57 this.name = name;58 }59 60 void makeSound() {61 System.out.println(name + " makes a sound");62 }63}6465class Dog extends Animal {66 Dog(String name) {67 super(name);68 }69 70 @Override71 void makeSound() {72 System.out.println(name + " barks: Woof!");73 }74 75 void fetch() { //?fetchmethod76 System.out.println(name + " fetches the ball!");77 }78}7980class Cat extends Animal {81 Cat(String name) {82 super(name);83 }84 85 @Override86 void makeSound() {87 System.out.println(nameWhiskers + " meows: Meow!");88 }outputWhiskers meows: Meow! === Upcasting (Automatic) ===void fetch()
pass 2 of 241 Dog backToDog = (Dog) mystery; //?downcast42 backToDog.fetch(); // Now we can call fetch!43 System.out.println("Downcasted: Animal → Dog");44 }45 46 // Method accepts ANY Animal //?acceptany47 static void feedAnimal(Animal a) {48 System.out.println("Feeding the animal...");49 a.makeSound(); // Works for any animal type50 }51}5253class Animal {54 String name;55 56 Animal(String name) {57 this.name = name;58 }59 60 void makeSound() {61 System.out.println(name + " makes a sound");62 }63}6465class Dog extends Animal {66 Dog(String name) {67 super(name);68 }69 70 @Override71 void makeSound() {72 System.out.println(name + " barks: Woof!");73 }74 75 void fetch() { //?fetchmethod76 System.out.println(nameScout + " fetches the ball!");77 }outputScout fetches the ball! Downcasted: Animal → Dog
Method called depends on actual object type, not variable type.
Compile-time polymorphism
Method overloading - same name, different parameters.
MethodOverloading.java
Replay: real traced execution (multi-file project)
// Compile-Time Polymorphism (Method Overloading)
public class MethodOverloading {
public static void main(String[] args) {
System.out.println("=== Method Overloading ===\n");
Calculator calc = new Calculator();
// Same method name, different parameters
System.out.println("add(5, 3) = " + calc.add(5, 3));
System.out.println("add(5, 3, 2) = " + calc.add(5, 3, 2));
System.out.println("add(5.5, 3.3) = " + calc.add(5.5, 3.3));
System.out.println("add(\"Hello\", \"World\") = " + calc.add("Hello", "World"));
System.out.println("\n=== Why 'Compile-Time'? ===");
System.out.println("""
Compiler decides which method to call
based on arguments at compile time.
add(5, 3) → calls add(int, int)
add(5, 3, 2) → calls add(int, int, int)
add(5.5, 3.3) → calls add(double, double)
add("A", "B") → calls add(String, String)
""");
System.out.println("=== Overloading Rules ===");
Printer printer = new Printer();
// Different number of parameters
printer.print("Hello");
printer.print("Hello", 3);
// Different parameter types
printer.print(42);
printer.print(3.14);
// Different parameter order
printer.display("Name", 1);
printer.display(1, "Name");
System.out.println("\n=== Return Type Doesn't Count ===");
System.out.println("""
// INVALID overloading:
int getValue() { return 1; }
double getValue() { return 1.0; } // ERROR!
Return type alone cannot distinguish methods.
Parameters must be different.
""");
}
}
class Calculator {
// Overloaded add methods
int add(int a, int b) {
return a + b;
}
int add(int a, int b, int c) {
return a + b + c;
}
double add(double a, double b) {
return a + b;
}
String add(String a, String b) {
return a + " " + b;
}
}
class Printer {
void print(String message) {
System.out.println("String: " + message);
}
void print(String message, int times) {
for (int i = 0; i < times; i++) {
System.out.println(message);
}
}
void print(int number) {
System.out.println("Integer: " + number);
}
void print(double number) {
System.out.println("Double: " + number);
}
void display(String label, int value) {
System.out.println(label + " = " + value);
}
void display(int value, String label) {
System.out.println(value + ": " + label);
}
}
calc ← ⟨Calculator A⟩
3public class MethodOverloading {4 public static void main(String[] args) {5 System.out.println("=== Method Overloading ===\n");6 7 Calculator calc→ ⟨Calculator A⟩ = new Calculator();8 9 // Same method name, different parameters //?samemethod10 System.out.println("add(5, 3) = " + calc.add(5, 3)); //?add2int11 System.out.println("add(5, 3, 2) = " + calc.add(5, 3, 2)); //?add3intoutput=== Method Overloading ===int add(int a, int b)
57int add(int a5, int b3) { //?addint58 return a5 + b3;59}System.out.println("add(5, 3) = " + calc.add(5, 3)); //?add2…
9// Same method name, different parameters //?samemethod10System.out.println("add(5, 3) = " + calc.add(5, 3)); //?add2int11System.out.println("add(5, 3, 2) = " + calc.add(5, 3, 2)); //?add3int12System.out.println("add(5.5, 3.3) = " + calc.add(5.5, 3.3)); //?add2doubleoutputadd(5, 3) = 8int add(int a, int b, int c)
61int add(int a5, int b3, int c2) { //?addthree62 return a5 + b3 + c2;63}System.out.println("add(5, 3, 2) = " + calc.add(5, 3, 2)); //?add3…
10System.out.println("add(5, 3) = " + calc.add(5, 3)); //?add2int11System.out.println("add(5, 3, 2) = " + calc.add(5, 3, 2)); //?add3int12System.out.println("add(5.5, 3.3) = " + calc.add(5.5, 3.3)); //?add2double13System.out.println("add(\"Hello\", \"World\") = " + calc.add("Hello", "World")); //?addstringoutputadd(5, 3, 2) = 10double add(double a, double b)
65double add(double a5.5, double b3.3) { //?adddouble66 return a5.5 + b3.3;67}System.out.println("add(5.5, 3.3) = " + calc.add(5.5, 3.3)); //?add2…
11System.out.println("add(5, 3, 2) = " + calc.add(5, 3, 2)); //?add3int12System.out.println("add(5.5, 3.3) = " + calc.add(5.5, 3.3)); //?add2double13System.out.println("add(\"Hello\", \"World\") = " + calc.add("Hello", "World")); //?addstringoutputadd(5.5, 3.3) = 8.8String add(String a, String b)
69String add(String aHello, String bWorld) { //?addstrings70 return aHello + " " + bWorld;71}printer ← ⟨Printer B⟩
12System.out.println("add(5.5, 3.3) = " + calc.add(5.5, 3.3)); //?add2double13System.out.println("add(\"Hello\", \"World\") = " + calc.add("Hello", "World")); //?addstring1415System.out.println("\n=== Why 'Compile-Time'? ===");16System.out.println("""17Compiler decides which method to call18based on arguments at compile time.1920add(5, 3) → calls add(int, int)21add(5, 3, 2) → calls add(int, int, int)22add(5.5, 3.3) → calls add(double, double)23add("A", "B") → calls add(String, String)24""");2526System.out.println("=== Overloading Rules ===");2728Printer printer→ ⟨Printer B⟩ = new Printer();2930// Different number of parameters //?diffcount31printer.print("Hello");32printer.print("Hello", 3);outputadd("Hello", "World") = Hello World === Why 'Compile-Time'? === Compiler decides which method to call based on arguments at compile time. add(5, 3) → calls add(int, int) add(5, 3, 2) → calls add(int, int, int) add(5.5, 3.3) → calls add(double, double) add("A", "B") → calls add(String, String) === Overloading Rules ===void print(String message)
30 // Different number of parameters //?diffcount31 printer.print("Hello");32 printer.print("Hello", 3);33 34 // Different parameter types //?difftypes35 printer.print(42);36 printer.print(3.14);37 38 // Different parameter order //?difforder39 printer.display("Name", 1);40 printer.display(1, "Name");41 42 System.out.println("\n=== Return Type Doesn't Count ===");43 System.out.println("""44 // INVALID overloading:45 int getValue() { return 1; }46 double getValue() { return 1.0; } // ERROR!47 48 Return type alone cannot distinguish methods.49 Parameters must be different.50 """);51 }52}5354class Calculator {55 // Overloaded add methods //?overloaded56 57 int add(int a, int b) { //?addint58 return a + b;59 }60 61 int add(int a, int b, int c) { //?addthree62 return a + b + c;63 }64 65 double add(double a, double b) { //?adddouble66 return a + b;67 }68 69 String add(String a, String b) { //?addstrings70 return a + " " + b;71 }72}7374class Printer {75 void print(String messageHello) { //?printstr76 System.out.println("String: " + messageHello);77 }outputString: Hellovoid print(String message, int times)
79void print(String messageHello, int times3) { //?printtimes80 for (int i = 0; i < times; i++) {for (int i = 0; i < times; i++)
pass 1 of 379void print(String message, int times) { //?printtimes80 for (int i0 = 0; i < times3; i++) {81 System.out.println(messageHello);82 }outputHelloAll 3 passes — pass 1 is the card above pass inumberlabelvalue1 0 — — — 2 1 — — — 3 2 42 Name 1 void print(int number)
34 // Different parameter types //?difftypes35 printer.print(42);36 printer.print(3.14);37 38 // Different parameter order //?difforder39 printer.display("Name", 1);40 printer.display(1, "Name");41 42 System.out.println("\n=== Return Type Doesn't Count ===");43 System.out.println("""44 // INVALID overloading:45 int getValue() { return 1; }46 double getValue() { return 1.0; } // ERROR!47 48 Return type alone cannot distinguish methods.49 Parameters must be different.50 """);51 }52}5354class Calculator {55 // Overloaded add methods //?overloaded56 57 int add(int a, int b) { //?addint58 return a + b;59 }60 61 int add(int a, int b, int c) { //?addthree62 return a + b + c;63 }64 65 double add(double a, double b) { //?adddouble66 return a + b;67 }68 69 String add(String a, String b) { //?addstrings70 return a + " " + b;71 }72}7374class Printer {75 void print(String message) { //?printstr76 System.out.println("String: " + message);77 }78 79 void print(String message, int times) { //?printtimes80 for (int i = 0; i < times; i++) {81 System.out.println(message);82 }83 }84 85 void print(int number42) { //?printint86 System.out.println("Integer: " + number42);87 }outputInteger: 42void print(double number)
35 printer.print(42);36 printer.print(3.14);37 38 // Different parameter order //?difforder39 printer.display("Name", 1);40 printer.display(1, "Name");41 42 System.out.println("\n=== Return Type Doesn't Count ===");43 System.out.println("""44 // INVALID overloading:45 int getValue() { return 1; }46 double getValue() { return 1.0; } // ERROR!47 48 Return type alone cannot distinguish methods.49 Parameters must be different.50 """);51 }52}5354class Calculator {55 // Overloaded add methods //?overloaded56 57 int add(int a, int b) { //?addint58 return a + b;59 }60 61 int add(int a, int b, int c) { //?addthree62 return a + b + c;63 }64 65 double add(double a, double b) { //?adddouble66 return a + b;67 }68 69 String add(String a, String b) { //?addstrings70 return a + " " + b;71 }72}7374class Printer {75 void print(String message) { //?printstr76 System.out.println("String: " + message);77 }78 79 void print(String message, int times) { //?printtimes80 for (int i = 0; i < times; i++) {81 System.out.println(message);82 }83 }84 85 void print(int number) { //?printint86 System.out.println("Integer: " + number);87 }88 89 void print(double number3.14) { //?printdouble90 System.out.println("Double: " + number3.14);91 }outputDouble: 3.14void display(String label, int value)
38 // Different parameter order //?difforder39 printer.display("Name", 1);40 printer.display(1, "Name");41 42 System.out.println("\n=== Return Type Doesn't Count ===");43 System.out.println("""44 // INVALID overloading:45 int getValue() { return 1; }46 double getValue() { return 1.0; } // ERROR!47 48 Return type alone cannot distinguish methods.49 Parameters must be different.50 """);51 }52}5354class Calculator {55 // Overloaded add methods //?overloaded56 57 int add(int a, int b) { //?addint58 return a + b;59 }60 61 int add(int a, int b, int c) { //?addthree62 return a + b + c;63 }64 65 double add(double a, double b) { //?adddouble66 return a + b;67 }68 69 String add(String a, String b) { //?addstrings70 return a + " " + b;71 }72}7374class Printer {75 void print(String message) { //?printstr76 System.out.println("String: " + message);77 }78 79 void print(String message, int times) { //?printtimes80 for (int i = 0; i < times; i++) {81 System.out.println(message);82 }83 }84 85 void print(int number) { //?printint86 System.out.println("Integer: " + number);87 }88 89 void print(double number) { //?printdouble90 System.out.println("Double: " + number);91 }92 93 void display(String labelName, int value1) { //?displaysi94 System.out.println(labelName + " = " + value1);95 }outputName = 1void display(int value, String label)
39 printer.display("Name", 1);40 printer.display(1, "Name");41 42 System.out.println("\n=== Return Type Doesn't Count ===");43 System.out.println("""44 // INVALID overloading:45 int getValue() { return 1; }46 double getValue() { return 1.0; } // ERROR!47 48 Return type alone cannot distinguish methods.49 Parameters must be different.50 """);51 }52}5354class Calculator {55 // Overloaded add methods //?overloaded56 57 int add(int a, int b) { //?addint58 return a + b;59 }60 61 int add(int a, int b, int c) { //?addthree62 return a + b + c;63 }64 65 double add(double a, double b) { //?adddouble66 return a + b;67 }68 69 String add(String a, String b) { //?addstrings70 return a + " " + b;71 }72}7374class Printer {75 void print(String message) { //?printstr76 System.out.println("String: " + message);77 }78 79 void print(String message, int times) { //?printtimes80 for (int i = 0; i < times; i++) {81 System.out.println(message);82 }83 }84 85 void print(int number) { //?printint86 System.out.println("Integer: " + number);87 }88 89 void print(double number) { //?printdouble90 System.out.println("Double: " + number);91 }92 93 void display(String label, int value) { //?displaysi94 System.out.println(label + " = " + value);95 }96 97 void display(int value1, String labelName) { //?displayis98 System.out.println(value1 + ": " + labelName);99 }output1: Name === Return Type Doesn't Count === // INVALID overloading: int getValue() { return 1; } double getValue() { return 1.0; } // ERROR! Return type alone cannot distinguish methods. Parameters must be different.
Compiler chooses method based on argument types at compile time.
overloading
Same method name, different parameters. Resolved at compile time.
Arrays of polymorphic objects
Store different subtypes in one array.
ArrayPolymorphism.java
Replay: real traced execution (multi-file project)
// Arrays and Collections with Polymorphism
public class ArrayPolymorphism {
public static void main(String[] args) {
System.out.println("=== Polymorphic Array ===\n");
// Array of parent type holding different child objects
Shape[] shapes = new Shape[4];
shapes[0] = new Circle(5.0);
shapes[1] = new Rectangle(4.0, 6.0);
shapes[2] = new Triangle(3.0, 4.0);
shapes[3] = new Circle(2.5);
// Process all shapes uniformly
System.out.println("Drawing all shapes:");
for (Shape shape : shapes) {
shape.draw();
}
System.out.println("\n=== Calculating Total Area ===");
double totalArea = 0;
for (Shape shape : shapes) {
double area = shape.getArea();
System.out.println("Area: " + String.format("%.2f", area));
totalArea += area;
}
System.out.println("Total: " + String.format("%.2f", totalArea));
System.out.println("\n=== Array Initialization Shorthand ===");
Shape[] moreShapes = {
new Circle(1.0),
new Rectangle(2.0, 3.0),
new Triangle(4.0, 5.0)
};
for (Shape s : moreShapes) {
s.draw();
}
System.out.println("\n=== Pass Array to Method ===");
printShapeInfo(shapes);
}
// Method accepts array of Shape
static void printShapeInfo(Shape[] shapes) {
System.out.println("Processing " + shapes.length + " shapes:");
for (int i = 0; i < shapes.length; i++) {
System.out.println((i + 1) + ". " + shapes[i].getName() +
" - Area: " + String.format("%.2f", shapes[i].getArea()));
}
}
}
class Shape {
String getName() {
return "Shape";
}
void draw() {
System.out.println("Drawing a shape");
}
double getArea() {
return 0;
}
}
class Circle extends Shape {
double radius;
Circle(double radius) {
this.radius = radius;
}
@Override
String getName() {
return "Circle (r=" + radius + ")";
}
@Override
void draw() {
System.out.println("Drawing circle with radius " + radius);
}
@Override
double getArea() {
return Math.PI * radius * radius;
}
}
class Rectangle extends Shape {
double width, height;
Rectangle(double width, double height) {
this.width = width;
this.height = height;
}
@Override
String getName() {
return "Rectangle (" + width + "x" + height + ")";
}
@Override
void draw() {
System.out.println("Drawing rectangle " + width + " x " + height);
}
@Override
double getArea() {
return width * height;
}
}
class Triangle extends Shape {
double base, height;
Triangle(double base, double height) {
this.base = base;
this.height = height;
}
@Override
String getName() {
return "Triangle (b=" + base + ", h=" + height + ")";
}
@Override
void draw() {
System.out.println("Drawing triangle with base " + base + " and height " + height);
}
@Override
double getArea() {
return 0.5 * base * height;
}
}
public static void main(String[] args)
3public class ArrayPolymorphism {4 public static void main(String[] args) {5 System.out.println("=== Polymorphic Array ===\n");6 7 // Array of parent type holding different child objects //?polyarray8 Shape[] shapes = new Shape[4];9 shapes[0]null = new Circle(5.0); //?addcircle10 shapes[1] = new Rectangle(4.0, 6.0);output=== Polymorphic Array ===this.radius ← 5.0, shapes[0] ← ⟨Circle A⟩
pass 1 of 38 Shape[] shapes = new Shape[4];9 shapes[0]→ ⟨Circle A⟩ = new Circle(5.0); //?addcircle10 shapes[1]null = new Rectangle(4.0, 6.0);11 shapes[2] = new Triangle(3.0, 4.0);12 shapes[3] = new Circle(2.5);13 14 // Process all shapes uniformly //?uniform15 System.out.println("Drawing all shapes:");16 for (Shape shape : shapes) {17 shape.draw(); //?drawcall18 }19 20 System.out.println("\n=== Calculating Total Area ===");21 22 double totalArea = 0;23 for (Shape shape : shapes) {24 double area = shape.getArea(); //?areacall25 System.out.println("Area: " + String.format("%.2f", area));26 totalArea += area;27 }28 System.out.println("Total: " + String.format("%.2f", totalArea));29 30 System.out.println("\n=== Array Initialization Shorthand ===");31 32 Shape[] moreShapes = { //?shorthand33 new Circle(1.0),34 new Rectangle(2.0, 3.0),35 new Triangle(4.0, 5.0)36 };37 38 for (Shape s : moreShapes) {39 s.draw();40 }41 42 System.out.println("\n=== Pass Array to Method ===");43 44 printShapeInfo(shapes); //?passarray45 }46 47 // Method accepts array of Shape //?arraymethod48 static void printShapeInfo(Shape[] shapes) {49 System.out.println("Processing " + shapes.length + " shapes:");50 for (int i = 0; i < shapes.length; i++) {51 System.out.println((i + 1) + ". " + shapes[i].getName() + 52 " - Area: " + String.format("%.2f", shapes[i].getArea()));53 }54 }55}5657class Shape {58 String getName() {59 return "Shape";60 }61 62 void draw() {63 System.out.println("Drawing a shape");64 }65 66 double getArea() {67 return 0;68 }69}7071class Circle extends Shape {72 double radius;73 74 Circle(double radius5.0) {75 this.radius→ 5.0 = radius5.0;76 }All 3 passes — pass 1 is the card above pass radiuswidthheightshapes[2]baseshapes.lengththis.radiusshapes[0]this.widththis.heightshapes[1]this.baseshapes[3]1 5.0 4.0 6.0 null 3.0 — 5.0 null → ⟨Circle A⟩ 4.0 6.0 null → ⟨Rectangle B⟩ 3.0 null 2 2.5 4.0 6.0 — 3.0 — 2.5 — — — — — null → ⟨Circle C⟩ 3 1.0 2.0 3.0 — 4.0 4 1.0 — 2.0 3.0 — 4.0 — this.width ← 4.0, this.height ← 6.0, shapes[1] ← ⟨Rectangle B⟩
pass 1 of 29 shapes[0] = new Circle(5.0); //?addcircle10 shapes[1]→ ⟨Rectangle B⟩ = new Rectangle(4.0, 6.0);11 shapes[2]null = new Triangle(3.0, 4.0);12 shapes[3] = new Circle(2.5);13 14 // Process all shapes uniformly //?uniform15 System.out.println("Drawing all shapes:");16 for (Shape shape : shapes) {17 shape.draw(); //?drawcall18 }19 20 System.out.println("\n=== Calculating Total Area ===");21 22 double totalArea = 0;23 for (Shape shape : shapes) {24 double area = shape.getArea(); //?areacall25 System.out.println("Area: " + String.format("%.2f", area));26 totalArea += area;27 }28 System.out.println("Total: " + String.format("%.2f", totalArea));29 30 System.out.println("\n=== Array Initialization Shorthand ===");31 32 Shape[] moreShapes = { //?shorthand33 new Circle(1.0),34 new Rectangle(2.0, 3.0),35 new Triangle(4.0, 5.0)36 };37 38 for (Shape s : moreShapes) {39 s.draw();40 }41 42 System.out.println("\n=== Pass Array to Method ===");43 44 printShapeInfo(shapes); //?passarray45 }46 47 // Method accepts array of Shape //?arraymethod48 static void printShapeInfo(Shape[] shapes) {49 System.out.println("Processing " + shapes.length + " shapes:");50 for (int i = 0; i < shapes.length; i++) {51 System.out.println((i + 1) + ". " + shapes[i].getName() + 52 " - Area: " + String.format("%.2f", shapes[i].getArea()));53 }54 }55}5657class Shape {58 String getName() {59 return "Shape";60 }61 62 void draw() {63 System.out.println("Drawing a shape");64 }65 66 double getArea() {67 return 0;68 }69}7071class Circle extends Shape {72 double radius;73 74 Circle(double radius) {75 this.radius = radius;76 }77 78 @Override79 String getName() {80 return "Circle (r=" + radius + ")";81 }82 83 @Override84 void draw() { //?circledraw85 System.out.println("Drawing circle with radius " + radius);86 }87 88 @Override89 double getArea() { //?circlearea90 return Math.PI * radius * radius;91 }92}9394class Rectangle extends Shape {95 double width, height;96 97 Rectangle(double width4.0, double height6.0) {98 this.width→ 4.0 = width4.0;99 this.height→ 6.0 = height6.0;100 }this.base ← 3.0, this.height ← 4.0, shapes[2] ← ⟨Triangle D⟩
pass 1 of 210 shapes[1] = new Rectangle(4.0, 6.0);11 shapes[2]→ ⟨Triangle D⟩ = new Triangle(3.0, 4.0);12 shapes[3]null = new Circle(2.5);13 14 // Process all shapes uniformly //?uniform15 System.out.println("Drawing all shapes:");16 for (Shape shape : shapes) {17 shape.draw(); //?drawcall18 }19 20 System.out.println("\n=== Calculating Total Area ===");21 22 double totalArea = 0;23 for (Shape shape : shapes) {24 double area = shape.getArea(); //?areacall25 System.out.println("Area: " + String.format("%.2f", area));26 totalArea += area;27 }28 System.out.println("Total: " + String.format("%.2f", totalArea));29 30 System.out.println("\n=== Array Initialization Shorthand ===");31 32 Shape[] moreShapes = { //?shorthand33 new Circle(1.0),34 new Rectangle(2.0, 3.0),35 new Triangle(4.0, 5.0)36 };37 38 for (Shape s : moreShapes) {39 s.draw();40 }41 42 System.out.println("\n=== Pass Array to Method ===");43 44 printShapeInfo(shapes); //?passarray45 }46 47 // Method accepts array of Shape //?arraymethod48 static void printShapeInfo(Shape[] shapes) {49 System.out.println("Processing " + shapes.length + " shapes:");50 for (int i = 0; i < shapes.length; i++) {51 System.out.println((i + 1) + ". " + shapes[i].getName() + 52 " - Area: " + String.format("%.2f", shapes[i].getArea()));53 }54 }55}5657class Shape {58 String getName() {59 return "Shape";60 }61 62 void draw() {63 System.out.println("Drawing a shape");64 }65 66 double getArea() {67 return 0;68 }69}7071class Circle extends Shape {72 double radius;73 74 Circle(double radius) {75 this.radius = radius;76 }77 78 @Override79 String getName() {80 return "Circle (r=" + radius + ")";81 }82 83 @Override84 void draw() { //?circledraw85 System.out.println("Drawing circle with radius " + radius);86 }87 88 @Override89 double getArea() { //?circlearea90 return Math.PI * radius * radius;91 }92}9394class Rectangle extends Shape {95 double width, height;96 97 Rectangle(double width, double height) {98 this.width = width;99 this.height = height;100 }101 102 @Override103 String getName() {104 return "Rectangle (" + width + "x" + height + ")";105 }106 107 @Override108 void draw() {109 System.out.println("Drawing rectangle " + width + " x " + height);110 }111 112 @Override113 double getArea() {114 return width * height;115 }116}117118class Triangle extends Shape {119 double base, height;120 121 Triangle(double base3.0, double height4.0) {122 this.base→ 3.0 = base3.0;123 this.height→ 4.0 = height4.0;124 }for (Shape shape : shapes)
pass 1 of 415System.out.println("Drawing all shapes:");16for (Shape shape⟨Circle A⟩ : shapes) {17 shape.draw(); //?drawcall18}All 4 passes — pass 1 is the card above pass shapewidthheightbase1 ⟨Circle A⟩ — — — 2 ⟨Rectangle B⟩ 4.0 6.0 — 3 ⟨Triangle D⟩ — 4.0 3.0 4 ⟨Circle C⟩ — — — @Override void draw()
pass 1 of 316 for (Shape shape : shapes) {17 shape.draw(); //?drawcall18 }19 20 System.out.println("\n=== Calculating Total Area ===");21 22 double totalArea = 0;23 for (Shape shape : shapes) {24 double area = shape.getArea(); //?areacall25 System.out.println("Area: " + String.format("%.2f", area));26 totalArea += area;27 }28 System.out.println("Total: " + String.format("%.2f", totalArea));29 30 System.out.println("\n=== Array Initialization Shorthand ===");31 32 Shape[] moreShapes = { //?shorthand33 new Circle(1.0),34 new Rectangle(2.0, 3.0),35 new Triangle(4.0, 5.0)36 };37 38 for (Shape s : moreShapes) {39 s.draw();40 }41 42 System.out.println("\n=== Pass Array to Method ===");43 44 printShapeInfo(shapes); //?passarray45 }46 47 // Method accepts array of Shape //?arraymethod48 static void printShapeInfo(Shape[] shapes) {49 System.out.println("Processing " + shapes.length + " shapes:");50 for (int i = 0; i < shapes.length; i++) {51 System.out.println((i + 1) + ". " + shapes[i].getName() + 52 " - Area: " + String.format("%.2f", shapes[i].getArea()));53 }54 }55}5657class Shape {58 String getName() {59 return "Shape";60 }61 62 void draw() {63 System.out.println("Drawing a shape");64 }65 66 double getArea() {67 return 0;68 }69}7071class Circle extends Shape {72 double radius;73 74 Circle(double radius) {75 this.radius = radius;76 }77 78 @Override79 String getName() {80 return "Circle (r=" + radius + ")";81 }82 83 @Override84 void draw() { //?circledraw85 System.out.println("Drawing circle with radius " + radius5.0);86 }outputDrawing circle with radius 5.0All 3 passes — pass 1 is the card above pass radiuswidthheightbaseshapes.lengthtotalArea1 5.0 4.0 6.0 3.0 — — 2 2.5 — — — — 0.0 3 1.0 2.0 3.0 4.0 4 — @Override void draw()
pass 1 of 216 for (Shape shape : shapes) {17 shape.draw(); //?drawcall18 }19 20 System.out.println("\n=== Calculating Total Area ===");21 22 double totalArea = 0;23 for (Shape shape : shapes) {24 double area = shape.getArea(); //?areacall25 System.out.println("Area: " + String.format("%.2f", area));26 totalArea += area;27 }28 System.out.println("Total: " + String.format("%.2f", totalArea));29 30 System.out.println("\n=== Array Initialization Shorthand ===");31 32 Shape[] moreShapes = { //?shorthand33 new Circle(1.0),34 new Rectangle(2.0, 3.0),35 new Triangle(4.0, 5.0)36 };37 38 for (Shape s : moreShapes) {39 s.draw();40 }41 42 System.out.println("\n=== Pass Array to Method ===");43 44 printShapeInfo(shapes); //?passarray45 }46 47 // Method accepts array of Shape //?arraymethod48 static void printShapeInfo(Shape[] shapes) {49 System.out.println("Processing " + shapes.length + " shapes:");50 for (int i = 0; i < shapes.length; i++) {51 System.out.println((i + 1) + ". " + shapes[i].getName() + 52 " - Area: " + String.format("%.2f", shapes[i].getArea()));53 }54 }55}5657class Shape {58 String getName() {59 return "Shape";60 }61 62 void draw() {63 System.out.println("Drawing a shape");64 }65 66 double getArea() {67 return 0;68 }69}7071class Circle extends Shape {72 double radius;73 74 Circle(double radius) {75 this.radius = radius;76 }77 78 @Override79 String getName() {80 return "Circle (r=" + radius + ")";81 }82 83 @Override84 void draw() { //?circledraw85 System.out.println("Drawing circle with radius " + radius);86 }87 88 @Override89 double getArea() { //?circlearea90 return Math.PI * radius * radius;91 }92}9394class Rectangle extends Shape {95 double width, height;96 97 Rectangle(double width, double height) {98 this.width = width;99 this.height = height;100 }101 102 @Override103 String getName() {104 return "Rectangle (" + width + "x" + height + ")";105 }106 107 @Override108 void draw() {109 System.out.println("Drawing rectangle " + width4.0 + " x " + height6.0);110 }outputDrawing rectangle 4.0 x 6.0@Override void draw()
pass 1 of 216 for (Shape shape : shapes) {17 shape.draw(); //?drawcall18 }19 20 System.out.println("\n=== Calculating Total Area ===");21 22 double totalArea = 0;23 for (Shape shape : shapes) {24 double area = shape.getArea(); //?areacall25 System.out.println("Area: " + String.format("%.2f", area));26 totalArea += area;27 }28 System.out.println("Total: " + String.format("%.2f", totalArea));29 30 System.out.println("\n=== Array Initialization Shorthand ===");31 32 Shape[] moreShapes = { //?shorthand33 new Circle(1.0),34 new Rectangle(2.0, 3.0),35 new Triangle(4.0, 5.0)36 };37 38 for (Shape s : moreShapes) {39 s.draw();40 }41 42 System.out.println("\n=== Pass Array to Method ===");43 44 printShapeInfo(shapes); //?passarray45 }46 47 // Method accepts array of Shape //?arraymethod48 static void printShapeInfo(Shape[] shapes) {49 System.out.println("Processing " + shapes.length + " shapes:");50 for (int i = 0; i < shapes.length; i++) {51 System.out.println((i + 1) + ". " + shapes[i].getName() + 52 " - Area: " + String.format("%.2f", shapes[i].getArea()));53 }54 }55}5657class Shape {58 String getName() {59 return "Shape";60 }61 62 void draw() {63 System.out.println("Drawing a shape");64 }65 66 double getArea() {67 return 0;68 }69}7071class Circle extends Shape {72 double radius;73 74 Circle(double radius) {75 this.radius = radius;76 }77 78 @Override79 String getName() {80 return "Circle (r=" + radius + ")";81 }82 83 @Override84 void draw() { //?circledraw85 System.out.println("Drawing circle with radius " + radius);86 }87 88 @Override89 double getArea() { //?circlearea90 return Math.PI * radius * radius;91 }92}9394class Rectangle extends Shape {95 double width, height;96 97 Rectangle(double width, double height) {98 this.width = width;99 this.height = height;100 }101 102 @Override103 String getName() {104 return "Rectangle (" + width + "x" + height + ")";105 }106 107 @Override108 void draw() {109 System.out.println("Drawing rectangle " + width + " x " + height);110 }111 112 @Override113 double getArea() {114 return width * height;115 }116}117118class Triangle extends Shape {119 double base, height;120 121 Triangle(double base, double height) {122 this.base = base;123 this.height = height;124 }125 126 @Override127 String getName() {128 return "Triangle (b=" + base + ", h=" + height + ")";129 }130 131 @Override132 void draw() {133 System.out.println("Drawing triangle with base " + base3.0 + " and height " + height4.0);134 }outputDrawing triangle with base 3.0 and height 4.0for (Shape shape : shapes)
pass 1 of 422double totalArea = 0;23for (Shape shape⟨Circle A⟩ : shapes) {24 double area = shape.getArea(); //?areacall25 System.out.println("Area: " + String.format("%.2f", area));All 4 passes — pass 1 is the card above pass shapewidthheightbase1 ⟨Circle A⟩ — — — 2 ⟨Rectangle B⟩ 4.0 6.0 — 3 ⟨Triangle D⟩ — 4.0 3.0 4 ⟨Circle C⟩ — — — @Override double getArea()
pass 1 of 488@Override89double getArea() { //?circlearea90 return Math.PI * radius5.0 * radius;91}All 4 passes — pass 1 is the card above pass radius1 5.0 2 2.5 3 5.0 4 2.5 area ← 78.53981633974483, totalArea ← 78.53981633974483
23for (Shape shape : shapes) {24 double area→ 78.53981633974483 = shape.getArea(); //?areacall25 System.out.println("Area: " + String.format("%.2f", area78.53981633974483));26 totalArea→ 78.53981633974483 += area78.53981633974483;27}outputArea: 78.54@Override double getArea()
pass 1 of 2112@Override113double getArea() {114 return width4.0 * height6.0;115}area ← 24.0, totalArea ← 102.53981633974483
23for (Shape shape : shapes) {24 double area→ 24.0 = shape.getArea(); //?areacall25 System.out.println("Area: " + String.format("%.2f", area24.0));26 totalArea→ 102.53981633974483 += area24.0;27}outputArea: 24.00@Override double getArea()
pass 1 of 2136@Override137double getArea() {138 return 0.5 * base3.0 * height4.0;139}area ← 6.0, totalArea ← 108.53981633974483
23for (Shape shape : shapes) {24 double area→ 6.0 = shape.getArea(); //?areacall25 System.out.println("Area: " + String.format("%.2f", area6.0));26 totalArea→ 108.53981633974483 += area6.0;27}outputArea: 6.00area ← 19.634954084936208, totalArea ← 128.17477042468104
23for (Shape shape : shapes) {24 double area→ 19.634954084936208 = shape.getArea(); //?areacall25 System.out.println("Area: " + String.format("%.2f", area19.634954084936208));26 totalArea→ 128.17477042468104 += area19.634954084936208;27}28System.out.println("Total: " + String.format("%.2f", totalArea128.17477042468104));2930System.out.println("\n=== Array Initialization Shorthand ===");3132Shape[] moreShapes = { //?shorthand33 new Circle(1.0),34 new Rectangle(2.0, 3.0),35 new Triangle(4.0, 5.0)36};outputArea: 19.63 Total: 128.17 === Array Initialization Shorthand ===this.width ← 2.0, this.height ← 3.0
pass 2 of 297Rectangle(double width2.0, double height3.0) {98 this.width→ 2.0 = width2.0;99 this.height→ 3.0 = height3.0;100}this.base ← 4.0, this.height ← 5.0
pass 2 of 232 Shape[] moreShapes = { //?shorthand33 new Circle(1.0),34 new Rectangle(2.0, 3.0),35 new Triangle(4.0, 5.0)36 };37 38 for (Shape s : moreShapes) {39 s.draw();40 }41 42 System.out.println("\n=== Pass Array to Method ===");43 44 printShapeInfo(shapes); //?passarray45 }46 47 // Method accepts array of Shape //?arraymethod48 static void printShapeInfo(Shape[] shapes) {49 System.out.println("Processing " + shapes.length + " shapes:");50 for (int i = 0; i < shapes.length; i++) {51 System.out.println((i + 1) + ". " + shapes[i].getName() + 52 " - Area: " + String.format("%.2f", shapes[i].getArea()));53 }54 }55}5657class Shape {58 String getName() {59 return "Shape";60 }61 62 void draw() {63 System.out.println("Drawing a shape");64 }65 66 double getArea() {67 return 0;68 }69}7071class Circle extends Shape {72 double radius;73 74 Circle(double radius) {75 this.radius = radius;76 }77 78 @Override79 String getName() {80 return "Circle (r=" + radius + ")";81 }82 83 @Override84 void draw() { //?circledraw85 System.out.println("Drawing circle with radius " + radius);86 }87 88 @Override89 double getArea() { //?circlearea90 return Math.PI * radius * radius;91 }92}9394class Rectangle extends Shape {95 double width, height;96 97 Rectangle(double width, double height) {98 this.width = width;99 this.height = height;100 }101 102 @Override103 String getName() {104 return "Rectangle (" + width + "x" + height + ")";105 }106 107 @Override108 void draw() {109 System.out.println("Drawing rectangle " + width + " x " + height);110 }111 112 @Override113 double getArea() {114 return width * height;115 }116}117118class Triangle extends Shape {119 double base, height;120 121 Triangle(double base4.0, double height5.0) {122 this.base→ 4.0 = base4.0;123 this.height→ 5.0 = height5.0;124 }for (Shape s : moreShapes)
pass 1 of 338for (Shape s⟨Circle E⟩ : moreShapes) {39 s.draw();40}All 3 passes — pass 1 is the card above pass swidthheightbaseshapes.lengthradius1 ⟨Circle E⟩ — — — — — 2 ⟨Rectangle F⟩ 2.0 3.0 — — — 3 ⟨Triangle G⟩ — 5.0 4.0 4 5.0 @Override void draw()
pass 2 of 238 for (Shape s : moreShapes) {39 s.draw();40 }41 42 System.out.println("\n=== Pass Array to Method ===");43 44 printShapeInfo(shapes); //?passarray45 }46 47 // Method accepts array of Shape //?arraymethod48 static void printShapeInfo(Shape[] shapes) {49 System.out.println("Processing " + shapes.length + " shapes:");50 for (int i = 0; i < shapes.length; i++) {51 System.out.println((i + 1) + ". " + shapes[i].getName() + 52 " - Area: " + String.format("%.2f", shapes[i].getArea()));53 }54 }55}5657class Shape {58 String getName() {59 return "Shape";60 }61 62 void draw() {63 System.out.println("Drawing a shape");64 }65 66 double getArea() {67 return 0;68 }69}7071class Circle extends Shape {72 double radius;73 74 Circle(double radius) {75 this.radius = radius;76 }77 78 @Override79 String getName() {80 return "Circle (r=" + radius + ")";81 }82 83 @Override84 void draw() { //?circledraw85 System.out.println("Drawing circle with radius " + radius);86 }87 88 @Override89 double getArea() { //?circlearea90 return Math.PI * radius * radius;91 }92}9394class Rectangle extends Shape {95 double width, height;96 97 Rectangle(double width, double height) {98 this.width = width;99 this.height = height;100 }101 102 @Override103 String getName() {104 return "Rectangle (" + width + "x" + height + ")";105 }106 107 @Override108 void draw() {109 System.out.println("Drawing rectangle " + width2.0 + " x " + height3.0);110 }outputDrawing rectangle 2.0 x 3.0@Override void draw()
pass 2 of 238 for (Shape s : moreShapes) {39 s.draw();40 }41 42 System.out.println("\n=== Pass Array to Method ===");43 44 printShapeInfo(shapes); //?passarray45 }46 47 // Method accepts array of Shape //?arraymethod48 static void printShapeInfo(Shape[] shapes) {49 System.out.println("Processing " + shapes.length + " shapes:");50 for (int i = 0; i < shapes.length; i++) {51 System.out.println((i + 1) + ". " + shapes[i].getName() + 52 " - Area: " + String.format("%.2f", shapes[i].getArea()));53 }54 }55}5657class Shape {58 String getName() {59 return "Shape";60 }61 62 void draw() {63 System.out.println("Drawing a shape");64 }65 66 double getArea() {67 return 0;68 }69}7071class Circle extends Shape {72 double radius;73 74 Circle(double radius) {75 this.radius = radius;76 }77 78 @Override79 String getName() {80 return "Circle (r=" + radius + ")";81 }82 83 @Override84 void draw() { //?circledraw85 System.out.println("Drawing circle with radius " + radius);86 }87 88 @Override89 double getArea() { //?circlearea90 return Math.PI * radius * radius;91 }92}9394class Rectangle extends Shape {95 double width, height;96 97 Rectangle(double width, double height) {98 this.width = width;99 this.height = height;100 }101 102 @Override103 String getName() {104 return "Rectangle (" + width + "x" + height + ")";105 }106 107 @Override108 void draw() {109 System.out.println("Drawing rectangle " + width + " x " + height);110 }111 112 @Override113 double getArea() {114 return width * height;115 }116}117118class Triangle extends Shape {119 double base, height;120 121 Triangle(double base, double height) {122 this.base = base;123 this.height = height;124 }125 126 @Override127 String getName() {128 return "Triangle (b=" + base + ", h=" + height + ")";129 }130 131 @Override132 void draw() {133 System.out.println("Drawing triangle with base " + base4.0 + " and height " + height5.0);134 }outputDrawing triangle with base 4.0 and height 5.0 === Pass Array to Method ===static void printShapeInfo(Shape[] shapes)
47// Method accepts array of Shape //?arraymethod48static void printShapeInfo(Shape[] shapes) {49 System.out.println("Processing " + shapes.length4 + " shapes:");50 for (int i = 0; i < shapes.length; i++) {outputProcessing 4 shapes:for (int i = 0; i < shapes.length; i++)
pass 1 of 449System.out.println("Processing " + shapes.length + " shapes:");50for (int i0 = 0; i < shapes.length4; i++) {51 System.out.println((i0 + 1) + ". " + shapes[i]⟨Circle A⟩.getName() + 52 " - Area: " + String.format("%.2f", shapes[i]⟨Circle A⟩.getArea()));53}All 4 passes — pass 1 is the card above pass ishapes[i]radiuswidthheightbase1 0 ⟨Circle A⟩ 5.0 — — — 2 1 ⟨Rectangle B⟩ — 4.0 6.0 — 3 2 ⟨Triangle D⟩ — — 4.0 3.0 4 3 ⟨Circle C⟩ 2.5 — — — @Override String getName()
pass 1 of 278@Override79String getName() {80 return "Circle (r=" + radius5.0 + ")";81}System.out.println((i + 1) + ". " + shapes[i].getName() +
50for (int i = 0; i < shapes.length; i++) {51 System.out.println((i0 + 1) + ". " + shapes[i]⟨Circle A⟩.getName() + 52 " - Area: " + String.format("%.2f", shapes[i]⟨Circle A⟩.getArea()));53}output1. Circle (r=5.0) - Area: 78.54@Override String getName()
102@Override103String getName() {104 return "Rectangle (" + width4.0 + "x" + height6.0 + ")";105}@Override double getArea()
pass 2 of 2112@Override113double getArea() {114 return width4.0 * height6.0;115}System.out.println((i + 1) + ". " + shapes[i].getName() +
50for (int i = 0; i < shapes.length; i++) {51 System.out.println((i1 + 1) + ". " + shapes[i]⟨Rectangle B⟩.getName() + 52 " - Area: " + String.format("%.2f", shapes[i]⟨Rectangle B⟩.getArea()));53}output2. Rectangle (4.0x6.0) - Area: 24.00@Override String getName()
126@Override127String getName() {128 return "Triangle (b=" + base3.0 + ", h=" + height4.0 + ")";129}@Override double getArea()
pass 2 of 2136@Override137double getArea() {138 return 0.5 * base3.0 * height4.0;139}System.out.println((i + 1) + ". " + shapes[i].getName() +
50for (int i = 0; i < shapes.length; i++) {51 System.out.println((i2 + 1) + ". " + shapes[i]⟨Triangle D⟩.getName() + 52 " - Area: " + String.format("%.2f", shapes[i]⟨Triangle D⟩.getArea()));53}output3. Triangle (b=3.0, h=4.0) - Area: 6.00@Override String getName()
pass 2 of 278@Override79String getName() {80 return "Circle (r=" + radius2.5 + ")";81}System.out.println((i + 1) + ". " + shapes[i].getName() +
44 printShapeInfo(shapes); //?passarray45}4647// Method accepts array of Shape //?arraymethod48static void printShapeInfo(Shape[] shapes) {49 System.out.println("Processing " + shapes.length + " shapes:");50 for (int i = 0; i < shapes.length; i++) {51 System.out.println((i3 + 1) + ". " + shapes[i]⟨Circle C⟩.getName() + 52 " - Area: " + String.format("%.2f", shapes[i]⟨Circle C⟩.getArea()));53 }output4. Circle (r=2.5) - Area: 19.63
Animal[] animals can hold Dog, Cat, Bird objects. Loop calls each's method.
Type checking with instanceof
Check actual type at runtime.
Instanceof.java
Replay: real traced execution (multi-file project)
// Type Checking with instanceof
public class Instanceof {
public static void main(String[] args) {
System.out.println("=== instanceof Operator ===\n");
// Create various animals
Animal[] animals = {
new Dog("Buddy"),
new Cat("Whiskers"),
new Dog("Max"),
new Bird("Tweety")
};
// Check types
for (Animal animal : animals) {
System.out.print(animal.name + ": ");
if (animal instanceof Dog) {
System.out.println("is a Dog");
} else if (animal instanceof Cat) {
System.out.println("is a Cat");
} else if (animal instanceof Bird) {
System.out.println("is a Bird");
}
}
System.out.println("\n=== Safe Downcasting ===");
Animal mystery = new Dog("Scout");
// UNSAFE: Could throw ClassCastException
// Cat cat = (Cat) mystery; // RuntimeException!
// SAFE: Check first
if (mystery instanceof Dog) {
Dog dog = (Dog) mystery;
dog.fetch(); // Now safe to call Dog methods
}
System.out.println("\n=== Pattern Matching (Java 16+) ===");
Animal animal = new Cat("Luna");
// Old way
if (animal instanceof Cat) {
Cat cat = (Cat) animal;
cat.scratch();
}
// New way: Pattern matching
if (animal instanceof Cat c) {
c.scratch(); // c is already Cat type!
}
System.out.println("\n=== Calling Type-Specific Methods ===");
for (Animal a : animals) {
a.makeSound(); // Works for all
// Type-specific behavior
if (a instanceof Dog d) {
d.fetch();
} else if (a instanceof Cat c) {
c.scratch();
} else if (a instanceof Bird b) {
b.fly();
}
}
}
}
class Animal {
String name;
Animal(String name) {
this.name = name;
}
void makeSound() {
System.out.println(name + " makes a sound");
}
}
class Dog extends Animal {
Dog(String name) {
super(name);
}
@Override
void makeSound() {
System.out.println(name + " barks!");
}
void fetch() {
System.out.println(name + " fetches the ball!");
}
}
class Cat extends Animal {
Cat(String name) {
super(name);
}
@Override
void makeSound() {
System.out.println(name + " meows!");
}
void scratch() {
System.out.println(name + " scratches!");
}
}
class Bird extends Animal {
Bird(String name) {
super(name);
}
@Override
void makeSound() {
System.out.println(name + " chirps!");
}
void fly() {
System.out.println(name + " flies away!");
}
}
// Type Checking with instanceof
public class Instanceof {
public static void main(String[] args) {
System.out.println("=== instanceof Operator ===\n");
// Create various animals
Animal[] animals = {
new Dog("Buddy"),
new Cat("Whiskers"),
new Dog("Max"),
new Bird("Tweety")
};
// Check types
for (Animal animal : animals) {
System.out.print(animal.name + ": ");
if (animal instanceof Dog) {
System.out.println("is a Dog");
} else if (animal instanceof Cat) {
System.out.println("is a Cat");
} else if (animal instanceof Bird) {
System.out.println("is a Bird");
}
}
System.out.println("\n=== Safe Downcasting ===");
Animal mystery = new Cat("Misty");
// UNSAFE: Could throw ClassCastException
// Cat cat = (Cat) mystery; // RuntimeException!
// SAFE: Check first
if (mystery instanceof Dog) {
Dog dog = (Dog) mystery;
dog.fetch(); // Now safe to call Dog methods
}
System.out.println("\n=== Pattern Matching (Java 16+) ===");
Animal animal = new Cat("Luna");
// Old way
if (animal instanceof Cat) {
Cat cat = (Cat) animal;
cat.scratch();
}
// New way: Pattern matching
if (animal instanceof Cat c) {
c.scratch(); // c is already Cat type!
}
System.out.println("\n=== Calling Type-Specific Methods ===");
for (Animal a : animals) {
a.makeSound(); // Works for all
// Type-specific behavior
if (a instanceof Dog d) {
d.fetch();
} else if (a instanceof Cat c) {
c.scratch();
} else if (a instanceof Bird b) {
b.fly();
}
}
}
}
class Animal {
String name;
Animal(String name) {
this.name = name;
}
void makeSound() {
System.out.println(name + " makes a sound");
}
}
class Dog extends Animal {
Dog(String name) {
super(name);
}
@Override
void makeSound() {
System.out.println(name + " barks!");
}
void fetch() {
System.out.println(name + " fetches the ball!");
}
}
class Cat extends Animal {
Cat(String name) {
super(name);
}
@Override
void makeSound() {
System.out.println(name + " meows!");
}
void scratch() {
System.out.println(name + " scratches!");
}
}
class Bird extends Animal {
Bird(String name) {
super(name);
}
@Override
void makeSound() {
System.out.println(name + " chirps!");
}
void fly() {
System.out.println(name + " flies away!");
}
}
// Type Checking with instanceof
public class Instanceof {
public static void main(String[] args) {
System.out.println("=== instanceof Operator ===\n");
// Create various animals
Animal[] animals = {
new Dog("Buddy"),
new Cat("Whiskers"),
new Dog("Max"),
new Bird("Tweety")
};
// Check types
for (Animal animal : animals) {
System.out.print(animal.name + ": ");
if (animal instanceof Dog) {
System.out.println("is a Dog");
} else if (animal instanceof Cat) {
System.out.println("is a Cat");
} else if (animal instanceof Bird) {
System.out.println("is a Bird");
}
}
System.out.println("\n=== Safe Downcasting ===");
Animal mystery = new Bird("Sky");
// UNSAFE: Could throw ClassCastException
// Cat cat = (Cat) mystery; // RuntimeException!
// SAFE: Check first
if (mystery instanceof Dog) {
Dog dog = (Dog) mystery;
dog.fetch(); // Now safe to call Dog methods
}
System.out.println("\n=== Pattern Matching (Java 16+) ===");
Animal animal = new Cat("Luna");
// Old way
if (animal instanceof Cat) {
Cat cat = (Cat) animal;
cat.scratch();
}
// New way: Pattern matching
if (animal instanceof Cat c) {
c.scratch(); // c is already Cat type!
}
System.out.println("\n=== Calling Type-Specific Methods ===");
for (Animal a : animals) {
a.makeSound(); // Works for all
// Type-specific behavior
if (a instanceof Dog d) {
d.fetch();
} else if (a instanceof Cat c) {
c.scratch();
} else if (a instanceof Bird b) {
b.fly();
}
}
}
}
class Animal {
String name;
Animal(String name) {
this.name = name;
}
void makeSound() {
System.out.println(name + " makes a sound");
}
}
class Dog extends Animal {
Dog(String name) {
super(name);
}
@Override
void makeSound() {
System.out.println(name + " barks!");
}
void fetch() {
System.out.println(name + " fetches the ball!");
}
}
class Cat extends Animal {
Cat(String name) {
super(name);
}
@Override
void makeSound() {
System.out.println(name + " meows!");
}
void scratch() {
System.out.println(name + " scratches!");
}
}
class Bird extends Animal {
Bird(String name) {
super(name);
}
@Override
void makeSound() {
System.out.println(name + " chirps!");
}
void fly() {
System.out.println(name + " flies away!");
}
}
public static void main(String[] args)
3public class Instanceof {4 public static void main(String[] args) {5 System.out.println("=== instanceof Operator ===\n");6 7 // Create various animals //?create8 Animal[] animals = {9 new Dog("Buddy"),10 new Cat("Whiskers"),11 new Dog("Max"),12 new Bird("Tweety")13 };output=== instanceof Operator ===this.name ← Buddy
pass 1 of 676Animal(String nameBuddy) {77 this.name→ Buddy = nameBuddy;78}All 6 passes — pass 1 is the card above pass namethis.namedoganimalcat1 Buddy Buddy — — — 2 Whiskers Whiskers — — — 3 Max Max — — — 4 Tweety Tweety — — — 5 Scout Scout ⟨Dog A⟩ — — 6 Luna Luna — ⟨Cat B⟩ ⟨Cat B⟩ Dog(String name)
pass 1 of 385class Dog extends Animal {86 Dog(String nameBuddy) {87 super(name);All 3 passes — pass 1 is the card above pass namemysterydoganimalcat1 Buddy — — — — 2 Max — — — — 3 Scout ⟨Dog A⟩ ⟨Dog A⟩ ⟨Cat B⟩ ⟨Cat B⟩ Cat(String name)
pass 1 of 2100class Cat extends Animal {101 Cat(String nameWhiskers) {102 super(name);Bird(String name)
7 // Create various animals //?create8 Animal[] animals = {9 new Dog("Buddy"),10 new Cat("Whiskers"),11 new Dog("Max"),12 new Bird("Tweety")13 };14 15 // Check types //?checktype16 for (Animal animal : animals) {17 System.out.print(animal.name + ": ");18 19 if (animal instanceof Dog) { //?isdog20 System.out.println("is a Dog");21 } else if (animal instanceof Cat) {22 System.out.println("is a Cat");23 } else if (animal instanceof Bird) {24 System.out.println("is a Bird");25 }26 }27 28 System.out.println("\n=== Safe Downcasting ===");29 30 Animal mystery = new Dog("Scout"); //@mystery=new Dog("Scout"), new Cat("Misty"), new Bird("Sky")31 32 // UNSAFE: Could throw ClassCastException //?unsafe33 // Cat cat = (Cat) mystery; // RuntimeException!34 35 // SAFE: Check first //?safe36 if (mystery instanceof Dog) {37 Dog dog = (Dog) mystery; //?safecast38 dog.fetch(); // Now safe to call Dog methods39 }40 41 System.out.println("\n=== Pattern Matching (Java 16+) ===");42 43 Animal animal = new Cat("Luna");44 45 // Old way //?oldway46 if (animal instanceof Cat) {47 Cat cat = (Cat) animal;48 cat.scratch();49 }50 51 // New way: Pattern matching //?newway52 if (animal instanceof Cat c) { //?patternmatch53 c.scratch(); // c is already Cat type!54 }55 56 System.out.println("\n=== Calling Type-Specific Methods ===");57 58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior //?typespecific62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() { //?fetchmethod96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() { //?scratchmethod111 System.out.println(name + " scratches!");112 }113}114115class Bird extends Animal {116 Bird(String nameTweety) {117 super(name);for (Animal animal : animals)
pass 1 of 415// Check types //?checktype16for (Animal animal⟨Dog C⟩ : animals) {17 System.out.print(animal.nameBuddy + ": ");outputBuddy:All 4 passes — pass 1 is the card above pass animalanimal.name1 ⟨Dog C⟩ Buddy 2 ⟨Cat D⟩ Whiskers 3 ⟨Dog E⟩ Max 4 ⟨Bird F⟩ Tweety if (animal instanceof Dog)
pass 1 of 219if (animal instanceof Dog) { //?isdog20 System.out.println("is a Dog");21} else if (animal instanceof Cat) {outputis a Dogif (animal instanceof Cat)
20 System.out.println("is a Dog");21} else if (animal instanceof Cat) {22 System.out.println("is a Cat");23} else if (animal instanceof Bird) {outputis a Catif (animal instanceof Dog)
pass 2 of 219if (animal instanceof Dog) { //?isdog20 System.out.println("is a Dog");21} else if (animal instanceof Cat) {outputis a Dogif (animal instanceof Bird)
22 System.out.println("is a Cat");23} else if (animal instanceof Bird) {24 System.out.println("is a Bird");25}outputis a BirdSystem.out.println(" === Safe Downcasting ===");
28System.out.println("\n=== Safe Downcasting ===");2930Animal mystery = new Dog("Scout"); //@mystery=new Dog("Scout"), new Cat("Misty"), new Bird("Sky")output === Safe Downcasting ===dog ← ⟨Dog A⟩
35// SAFE: Check first //?safe36if (mystery instanceof Dog) {37 Dog dog→ ⟨Dog A⟩ = (Dog) mystery; //?safecast38 dog.fetch(); // Now safe to call Dog methods39}void fetch()
pass 1 of 337 Dog dog = (Dog) mystery; //?safecast38 dog.fetch(); // Now safe to call Dog methods39 }40 41 System.out.println("\n=== Pattern Matching (Java 16+) ===");42 43 Animal animal = new Cat("Luna");44 45 // Old way //?oldway46 if (animal instanceof Cat) {47 Cat cat = (Cat) animal;48 cat.scratch();49 }50 51 // New way: Pattern matching //?newway52 if (animal instanceof Cat c) { //?patternmatch53 c.scratch(); // c is already Cat type!54 }55 56 System.out.println("\n=== Calling Type-Specific Methods ===");57 58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior //?typespecific62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() { //?fetchmethod96 System.out.println(nameScout + " fetches the ball!");97 }outputScout fetches the ball! === Pattern Matching (Java 16+) ===All 3 passes — pass 1 is the card above pass nameanimalcat1 Scout ⟨Cat B⟩ ⟨Cat B⟩ 2 Buddy — — 3 Max — — animal ← ⟨Cat B⟩
pass 2 of 243 Animal animal→ ⟨Cat B⟩ = new Cat("Luna");44 45 // Old way //?oldway46 if (animal instanceof Cat) {47 Cat cat = (Cat) animal;48 cat.scratch();49 }50 51 // New way: Pattern matching //?newway52 if (animal instanceof Cat c) { //?patternmatch53 c.scratch(); // c is already Cat type!54 }55 56 System.out.println("\n=== Calling Type-Specific Methods ===");57 58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior //?typespecific62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() { //?fetchmethod96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String nameLuna) {102 super(name);cat ← ⟨Cat B⟩
45// Old way //?oldway46if (animal instanceof Cat) {47 Cat cat→ ⟨Cat B⟩ = (Cat) animal;48 cat.scratch();49}void scratch()
pass 1 of 347 Cat cat = (Cat) animal;48 cat.scratch();49 }50 51 // New way: Pattern matching //?newway52 if (animal instanceof Cat c) { //?patternmatch53 c.scratch(); // c is already Cat type!54 }55 56 System.out.println("\n=== Calling Type-Specific Methods ===");57 58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior //?typespecific62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() { //?fetchmethod96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() { //?scratchmethod111 System.out.println(nameLuna + " scratches!");112 }outputLuna scratches!All 3 passes — pass 1 is the card above pass name1 Luna 2 Luna 3 Whiskers for (Animal a : animals)
pass 1 of 458for (Animal a⟨Dog C⟩ : animals) {59 a.makeSound(); // Works for allAll 4 passes — pass 1 is the card above pass aname1 ⟨Dog C⟩ Buddy 2 ⟨Cat D⟩ Whiskers 3 ⟨Dog E⟩ Max 4 ⟨Bird F⟩ Tweety @Override void makeSound()
pass 1 of 258 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior //?typespecific62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(nameBuddy + " barks!");93 }outputBuddy barks!@Override void makeSound()
58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior //?typespecific62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() { //?fetchmethod96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(nameWhiskers + " meows!");108 }outputWhiskers meows!@Override void makeSound()
pass 2 of 258 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior //?typespecific62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(nameMax + " barks!");93 }outputMax barks!@Override void makeSound()
58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior //?typespecific62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() { //?fetchmethod96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() { //?scratchmethod111 System.out.println(name + " scratches!");112 }113}114115class Bird extends Animal {116 Bird(String name) {117 super(name);118 }119 120 @Override121 void makeSound() {122 System.out.println(nameTweety + " chirps!");123 }outputTweety chirps!void fly()
66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() { //?fetchmethod96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() { //?scratchmethod111 System.out.println(name + " scratches!");112 }113}114115class Bird extends Animal {116 Bird(String name) {117 super(name);118 }119 120 @Override121 void makeSound() {122 System.out.println(name + " chirps!");123 }124 125 void fly() { //?flymethod126 System.out.println(nameTweety + " flies away!");127 }outputTweety flies away!
public static void main(String[] args)
3public class Instanceof {4 public static void main(String[] args) {5 System.out.println("=== instanceof Operator ===\n");6 7 // Create various animals8 Animal[] animals = {9 new Dog("Buddy"),10 new Cat("Whiskers"),11 new Dog("Max"),12 new Bird("Tweety")13 };output=== instanceof Operator ===this.name ← Buddy
pass 1 of 676Animal(String nameBuddy) {77 this.name→ Buddy = nameBuddy;78}All 6 passes — pass 1 is the card above pass namethis.namecat1 Buddy Buddy — 2 Whiskers Whiskers — 3 Max Max — 4 Tweety Tweety — 5 Misty Misty — 6 Luna Luna ⟨Cat A⟩ Dog(String name)
pass 1 of 285class Dog extends Animal {86 Dog(String nameBuddy) {87 super(name);Cat(String name)
pass 1 of 3100class Cat extends Animal {101 Cat(String nameWhiskers) {102 super(name);All 3 passes — pass 1 is the card above pass namemysteryanimalcat1 Whiskers — — — 2 Misty ⟨Cat B⟩ — — 3 Luna — ⟨Cat A⟩ ⟨Cat A⟩ Dog(String name)
pass 2 of 285class Dog extends Animal {86 Dog(String nameMax) {87 super(name);Bird(String name)
7 // Create various animals8 Animal[] animals = {9 new Dog("Buddy"),10 new Cat("Whiskers"),11 new Dog("Max"),12 new Bird("Tweety")13 };14 15 // Check types16 for (Animal animal : animals) {17 System.out.print(animal.name + ": ");18 19 if (animal instanceof Dog) {20 System.out.println("is a Dog");21 } else if (animal instanceof Cat) {22 System.out.println("is a Cat");23 } else if (animal instanceof Bird) {24 System.out.println("is a Bird");25 }26 }27 28 System.out.println("\n=== Safe Downcasting ===");29 30 Animal mystery = new Cat("Misty");31 32 // UNSAFE: Could throw ClassCastException33 // Cat cat = (Cat) mystery; // RuntimeException!34 35 // SAFE: Check first36 if (mystery instanceof Dog) {37 Dog dog = (Dog) mystery;38 dog.fetch(); // Now safe to call Dog methods39 }40 41 System.out.println("\n=== Pattern Matching (Java 16+) ===");42 43 Animal animal = new Cat("Luna");44 45 // Old way46 if (animal instanceof Cat) {47 Cat cat = (Cat) animal;48 cat.scratch();49 }50 51 // New way: Pattern matching52 if (animal instanceof Cat c) {53 c.scratch(); // c is already Cat type!54 }55 56 System.out.println("\n=== Calling Type-Specific Methods ===");57 58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() {111 System.out.println(name + " scratches!");112 }113}114115class Bird extends Animal {116 Bird(String nameTweety) {117 super(name);for (Animal animal : animals)
pass 1 of 415// Check types16for (Animal animal⟨Dog C⟩ : animals) {17 System.out.print(animal.nameBuddy + ": ");outputBuddy:All 4 passes — pass 1 is the card above pass animalanimal.name1 ⟨Dog C⟩ Buddy 2 ⟨Cat D⟩ Whiskers 3 ⟨Dog E⟩ Max 4 ⟨Bird F⟩ Tweety if (animal instanceof Dog)
pass 1 of 219if (animal instanceof Dog) {20 System.out.println("is a Dog");21} else if (animal instanceof Cat) {outputis a Dogif (animal instanceof Cat)
20 System.out.println("is a Dog");21} else if (animal instanceof Cat) {22 System.out.println("is a Cat");23} else if (animal instanceof Bird) {outputis a Catif (animal instanceof Dog)
pass 2 of 219if (animal instanceof Dog) {20 System.out.println("is a Dog");21} else if (animal instanceof Cat) {outputis a Dogif (animal instanceof Bird)
22 System.out.println("is a Cat");23} else if (animal instanceof Bird) {24 System.out.println("is a Bird");25}outputis a BirdSystem.out.println(" === Safe Downcasting ===");
28System.out.println("\n=== Safe Downcasting ===");2930Animal mystery = new Cat("Misty");output === Safe Downcasting ===cat ← ⟨Cat A⟩
45// Old way46if (animal instanceof Cat) {47 Cat cat→ ⟨Cat A⟩ = (Cat) animal;48 cat.scratch();49}void scratch()
pass 1 of 347 Cat cat = (Cat) animal;48 cat.scratch();49 }50 51 // New way: Pattern matching52 if (animal instanceof Cat c) {53 c.scratch(); // c is already Cat type!54 }55 56 System.out.println("\n=== Calling Type-Specific Methods ===");57 58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() {111 System.out.println(nameLuna + " scratches!");112 }outputLuna scratches!All 3 passes — pass 1 is the card above pass name1 Luna 2 Luna 3 Whiskers for (Animal a : animals)
pass 1 of 458for (Animal a⟨Dog C⟩ : animals) {59 a.makeSound(); // Works for allAll 4 passes — pass 1 is the card above pass aname1 ⟨Dog C⟩ Buddy 2 ⟨Cat D⟩ Whiskers 3 ⟨Dog E⟩ Max 4 ⟨Bird F⟩ Tweety @Override void makeSound()
pass 1 of 258 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(nameBuddy + " barks!");93 }outputBuddy barks!void fetch()
pass 1 of 262 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(nameBuddy + " fetches the ball!");97 }outputBuddy fetches the ball!@Override void makeSound()
58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(nameWhiskers + " meows!");108 }outputWhiskers meows!@Override void makeSound()
pass 2 of 258 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(nameMax + " barks!");93 }outputMax barks!void fetch()
pass 2 of 262 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(nameMax + " fetches the ball!");97 }outputMax fetches the ball!@Override void makeSound()
58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() {111 System.out.println(name + " scratches!");112 }113}114115class Bird extends Animal {116 Bird(String name) {117 super(name);118 }119 120 @Override121 void makeSound() {122 System.out.println(nameTweety + " chirps!");123 }outputTweety chirps!void fly()
66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() {111 System.out.println(name + " scratches!");112 }113}114115class Bird extends Animal {116 Bird(String name) {117 super(name);118 }119 120 @Override121 void makeSound() {122 System.out.println(name + " chirps!");123 }124 125 void fly() {126 System.out.println(nameTweety + " flies away!");127 }outputTweety flies away!
public static void main(String[] args)
3public class Instanceof {4 public static void main(String[] args) {5 System.out.println("=== instanceof Operator ===\n");6 7 // Create various animals8 Animal[] animals = {9 new Dog("Buddy"),10 new Cat("Whiskers"),11 new Dog("Max"),12 new Bird("Tweety")13 };output=== instanceof Operator ===this.name ← Buddy
pass 1 of 676Animal(String nameBuddy) {77 this.name→ Buddy = nameBuddy;78}All 6 passes — pass 1 is the card above pass namethis.namemysteryanimalcat1 Buddy Buddy — — — 2 Whiskers Whiskers — — — 3 Max Max — — — 4 Tweety Tweety — — — 5 Sky Sky ⟨Bird A⟩ — — 6 Luna Luna — ⟨Cat B⟩ ⟨Cat B⟩ Dog(String name)
pass 1 of 285class Dog extends Animal {86 Dog(String nameBuddy) {87 super(name);Cat(String name)
pass 1 of 2100class Cat extends Animal {101 Cat(String nameWhiskers) {102 super(name);Dog(String name)
pass 2 of 285class Dog extends Animal {86 Dog(String nameMax) {87 super(name);Bird(String name)
pass 1 of 27 // Create various animals8 Animal[] animals = {9 new Dog("Buddy"),10 new Cat("Whiskers"),11 new Dog("Max"),12 new Bird("Tweety")13 };14 15 // Check types16 for (Animal animal : animals) {17 System.out.print(animal.name + ": ");18 19 if (animal instanceof Dog) {20 System.out.println("is a Dog");21 } else if (animal instanceof Cat) {22 System.out.println("is a Cat");23 } else if (animal instanceof Bird) {24 System.out.println("is a Bird");25 }26 }27 28 System.out.println("\n=== Safe Downcasting ===");29 30 Animal mystery = new Bird("Sky");31 32 // UNSAFE: Could throw ClassCastException33 // Cat cat = (Cat) mystery; // RuntimeException!34 35 // SAFE: Check first36 if (mystery instanceof Dog) {37 Dog dog = (Dog) mystery;38 dog.fetch(); // Now safe to call Dog methods39 }40 41 System.out.println("\n=== Pattern Matching (Java 16+) ===");42 43 Animal animal = new Cat("Luna");44 45 // Old way46 if (animal instanceof Cat) {47 Cat cat = (Cat) animal;48 cat.scratch();49 }50 51 // New way: Pattern matching52 if (animal instanceof Cat c) {53 c.scratch(); // c is already Cat type!54 }55 56 System.out.println("\n=== Calling Type-Specific Methods ===");57 58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() {111 System.out.println(name + " scratches!");112 }113}114115class Bird extends Animal {116 Bird(String nameTweety) {117 super(name);for (Animal animal : animals)
pass 1 of 415// Check types16for (Animal animal⟨Dog C⟩ : animals) {17 System.out.print(animal.nameBuddy + ": ");outputBuddy:All 4 passes — pass 1 is the card above pass animalanimal.name1 ⟨Dog C⟩ Buddy 2 ⟨Cat D⟩ Whiskers 3 ⟨Dog E⟩ Max 4 ⟨Bird F⟩ Tweety if (animal instanceof Dog)
pass 1 of 219if (animal instanceof Dog) {20 System.out.println("is a Dog");21} else if (animal instanceof Cat) {outputis a Dogif (animal instanceof Cat)
20 System.out.println("is a Dog");21} else if (animal instanceof Cat) {22 System.out.println("is a Cat");23} else if (animal instanceof Bird) {outputis a Catif (animal instanceof Dog)
pass 2 of 219if (animal instanceof Dog) {20 System.out.println("is a Dog");21} else if (animal instanceof Cat) {outputis a Dogif (animal instanceof Bird)
22 System.out.println("is a Cat");23} else if (animal instanceof Bird) {24 System.out.println("is a Bird");25}outputis a BirdSystem.out.println(" === Safe Downcasting ===");
28System.out.println("\n=== Safe Downcasting ===");2930Animal mystery = new Bird("Sky");output === Safe Downcasting ===mystery ← ⟨Bird A⟩
pass 2 of 230 Animal mystery→ ⟨Bird A⟩ = new Bird("Sky");31 32 // UNSAFE: Could throw ClassCastException33 // Cat cat = (Cat) mystery; // RuntimeException!34 35 // SAFE: Check first36 if (mystery instanceof Dog) {37 Dog dog = (Dog) mystery;38 dog.fetch(); // Now safe to call Dog methods39 }40 41 System.out.println("\n=== Pattern Matching (Java 16+) ===");42 43 Animal animal = new Cat("Luna");44 45 // Old way46 if (animal instanceof Cat) {47 Cat cat = (Cat) animal;48 cat.scratch();49 }50 51 // New way: Pattern matching52 if (animal instanceof Cat c) {53 c.scratch(); // c is already Cat type!54 }55 56 System.out.println("\n=== Calling Type-Specific Methods ===");57 58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() {111 System.out.println(name + " scratches!");112 }113}114115class Bird extends Animal {116 Bird(String nameSky) {117 super(name);output === Pattern Matching (Java 16+) ===animal ← ⟨Cat B⟩
pass 2 of 243 Animal animal→ ⟨Cat B⟩ = new Cat("Luna");44 45 // Old way46 if (animal instanceof Cat) {47 Cat cat = (Cat) animal;48 cat.scratch();49 }50 51 // New way: Pattern matching52 if (animal instanceof Cat c) {53 c.scratch(); // c is already Cat type!54 }55 56 System.out.println("\n=== Calling Type-Specific Methods ===");57 58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String nameLuna) {102 super(name);cat ← ⟨Cat B⟩
45// Old way46if (animal instanceof Cat) {47 Cat cat→ ⟨Cat B⟩ = (Cat) animal;48 cat.scratch();49}void scratch()
pass 1 of 347 Cat cat = (Cat) animal;48 cat.scratch();49 }50 51 // New way: Pattern matching52 if (animal instanceof Cat c) {53 c.scratch(); // c is already Cat type!54 }55 56 System.out.println("\n=== Calling Type-Specific Methods ===");57 58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() {111 System.out.println(nameLuna + " scratches!");112 }outputLuna scratches!All 3 passes — pass 1 is the card above pass name1 Luna 2 Luna 3 Whiskers for (Animal a : animals)
pass 1 of 458for (Animal a⟨Dog C⟩ : animals) {59 a.makeSound(); // Works for allAll 4 passes — pass 1 is the card above pass aname1 ⟨Dog C⟩ Buddy 2 ⟨Cat D⟩ Whiskers 3 ⟨Dog E⟩ Max 4 ⟨Bird F⟩ Tweety @Override void makeSound()
pass 1 of 258 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(nameBuddy + " barks!");93 }outputBuddy barks!void fetch()
pass 1 of 262 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(nameBuddy + " fetches the ball!");97 }outputBuddy fetches the ball!@Override void makeSound()
58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(nameWhiskers + " meows!");108 }outputWhiskers meows!@Override void makeSound()
pass 2 of 258 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(nameMax + " barks!");93 }outputMax barks!void fetch()
pass 2 of 262 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(nameMax + " fetches the ball!");97 }outputMax fetches the ball!@Override void makeSound()
58 for (Animal a : animals) {59 a.makeSound(); // Works for all60 61 // Type-specific behavior62 if (a instanceof Dog d) {63 d.fetch();64 } else if (a instanceof Cat c) {65 c.scratch();66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() {111 System.out.println(name + " scratches!");112 }113}114115class Bird extends Animal {116 Bird(String name) {117 super(name);118 }119 120 @Override121 void makeSound() {122 System.out.println(nameTweety + " chirps!");123 }outputTweety chirps!void fly()
66 } else if (a instanceof Bird b) {67 b.fly();68 }69 }70 }71}7273class Animal {74 String name;75 76 Animal(String name) {77 this.name = name;78 }79 80 void makeSound() {81 System.out.println(name + " makes a sound");82 }83}8485class Dog extends Animal {86 Dog(String name) {87 super(name);88 }89 90 @Override91 void makeSound() {92 System.out.println(name + " barks!");93 }94 95 void fetch() {96 System.out.println(name + " fetches the ball!");97 }98}99100class Cat extends Animal {101 Cat(String name) {102 super(name);103 }104 105 @Override106 void makeSound() {107 System.out.println(name + " meows!");108 }109 110 void scratch() {111 System.out.println(name + " scratches!");112 }113}114115class Bird extends Animal {116 Bird(String name) {117 super(name);118 }119 120 @Override121 void makeSound() {122 System.out.println(name + " chirps!");123 }124 125 void fly() {126 System.out.println(nameTweety + " flies away!");127 }outputTweety flies away!
if (animal instanceof Dog) checks real type before casting.
instanceof
Check object's actual type: `obj instanceof Type`. Returns boolean.
Exercise: Practical.java
Build a payment processing system with polymorphism