Sealed Classes - Java Programming

Your Result type should only be Success or Failure - nothing else. Sealed classes restrict which classes can extend them. The compiler knows all possibilities, enabling exhaustive pattern matching in switch expressions.

Basic sealed class

Restrict which classes can extend.

                            SealedBasics.java
                        
Replay: real traced execution (multi-file project)

                            // Basic Sealed Class Syntax

// Sealed class - restricts who can extend
sealed class Animal permits Dog, Cat, Bird {
    private String name;

    Animal(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void describe() {
        System.out.println("I am " + name);
    }
}

// Permitted subclass - must be final, sealed, or non-sealed
final class Dog extends Animal {
    Dog(String name) {
        super(name);
    }

    public void bark() {
        System.out.println(getName() + " says: Woof!");
    }
}

final class Cat extends Animal {
    Cat(String name) {
        super(name);
    }

    public void meow() {
        System.out.println(getName() + " says: Meow!");
    }
}

final class Bird extends Animal {
    Bird(String name) {
        super(name);
    }

    public void chirp() {
        System.out.println(getName() + " says: Chirp!");
    }
}

// This would NOT compile!
// class Fish extends Animal { }  // Error: Fish is not in permits list

public class SealedBasics {
    public static void main(String[] args) {
        System.out.println("=== Sealed Classes Basics ===\n");

        // Create permitted subclasses
        Dog dog = new Dog("Buddy");
        Cat cat = new Cat("Whiskers");
        Bird bird = new Bird("Tweety");

        dog.describe();
        dog.bark();

        System.out.println();
        cat.describe();
        cat.meow();

        System.out.println();
        bird.describe();
        bird.chirp();

        System.out.println("\n=== Polymorphism Works ===");

        Animal[] animals = {dog, cat, bird};
        for (Animal animal : animals) {
            animal.describe();
        }

        System.out.println("\n=== Why Sealed Classes? ===");
        System.out.println("""
            1. CONTROL: Know exactly which classes extend yours
            2. SAFETY: Prevent unexpected subclasses
            3. EXHAUSTIVE: Switch can cover all cases
            4. DOCUMENTATION: Permits list shows intent

            Without sealed:
            - Anyone can extend your class
            - Switch might miss cases
            - Library users could break assumptions

            With sealed:
            - Only permitted classes can extend
            - Compiler knows all subclasses
            - Pattern matching is exhaustive
            """);

        System.out.println("=== Sealed Class Rules ===");
        System.out.println("""
            1. Use 'sealed' modifier on class
            2. Use 'permits' to list allowed subclasses
            3. Each permitted class must:
               - Be in same module (or package if unnamed)
               - Directly extend the sealed class
               - Be 'final', 'sealed', or 'non-sealed'
            """);
    }
}

                        
1public static void main(String[] args)⋯54public class SealedBasics {55    public static void main(String[] args) {56        System.out.println("=== Sealed Classes Basics ===\n");57        58        // Create permitted subclasses //?createobjects59        Dog dog = new Dog("Buddy");60        Cat cat = new Cat("Whiskers");⋯output=== Sealed Classes Basics ===
2this.name ← Buddypass 1 of 3⋯7Animal(String nameBuddy) {8    this.name→ Buddy = nameBuddy;9}⋯All 3 passes — pass 1 is the card abovepassnamethis.name
1BuddyBuddy
2WhiskersWhiskers
3TweetyTweety
3Dog(String name)⋯21final class Dog extends Animal { //?finalsubclass22    Dog(String nameBuddy) {23        super(name);⋯
4dog ← ⟨Dog A⟩⋯58// Create permitted subclasses //?createobjects59Dog dog→ ⟨Dog A⟩ = new Dog("Buddy");60Cat cat = new Cat("Whiskers");61Bird bird = new Bird("Tweety");⋯
5Cat(String name)⋯31final class Cat extends Animal { //?anothersubclass32    Cat(String nameWhiskers) {33        super(name);⋯
6cat ← ⟨Cat B⟩⋯59Dog dog = new Dog("Buddy");60Cat cat→ ⟨Cat B⟩ = new Cat("Whiskers");61Bird bird = new Bird("Tweety");⋯
7Bird(String name)⋯41final class Bird extends Animal {42    Bird(String nameTweety) {43        super(name);⋯
8bird ← ⟨Bird C⟩⋯60Cat cat = new Cat("Whiskers");61Bird bird→ ⟨Bird C⟩ = new Bird("Tweety");6263dog.describe();64dog.bark();⋯
9public void describe()pass 1 of 6⋯15public void describe() {16    System.out.println("I am " + nameBuddy);17}⋯outputI am BuddyAll 6 passes — pass 1 is the card abovepassname
1Buddy
2Whiskers
3Tweety
4Buddy
5Whiskers
6Tweety
10dog.describe();⋯63dog.describe();64dog.bark();⋯
11public String getName()pass 1 of 3⋯11public String getName() {12    return nameBuddy;13}⋯All 3 passes — pass 1 is the card abovepassname
1Buddy
2Whiskers
3Tweety
12System.out.println(getName() + " says: Woof!");⋯26public void bark() {27    System.out.println(getName() + " says: Woof!");28}⋯outputBuddy says: Woof!
13dog.bark();⋯63dog.describe();64dog.bark();6566System.out.println();67cat.describe();68cat.meow();⋯
14cat.describe();⋯66System.out.println();67cat.describe();68cat.meow();⋯
15System.out.println(getName() + " says: Meow!");⋯36public void meow() {37    System.out.println(getName() + " says: Meow!");38}⋯outputWhiskers says: Meow!
16cat.meow();⋯67cat.describe();68cat.meow();6970System.out.println();71bird.describe();72bird.chirp();⋯
17bird.describe();⋯70System.out.println();71bird.describe();72bird.chirp();⋯
18System.out.println(getName() + " says: Chirp!");⋯46public void chirp() {47    System.out.println(getName() + " says: Chirp!");48}⋯outputTweety says: Chirp!
19Animal[] animals = {dog, cat, bird}; //?polymorphism⋯71bird.describe();72bird.chirp();7374System.out.println("\n=== Polymorphism Works ===");7576Animal[] animals = {dog, cat, bird}; //?polymorphism77for (Animal animal : animals) {⋯output
=== Polymorphism Works ===
20for (Animal animal : animals)pass 1 of 3⋯76Animal[] animals = {dog, cat, bird}; //?polymorphism77for (Animal animal⟨Dog A⟩ : animals) {78    animal.describe();79}⋯All 3 passes — pass 1 is the card abovepassanimal
1⟨Dog A⟩
2⟨Cat B⟩
3⟨Bird C⟩
21animal.describe();⋯77for (Animal animal : animals) {78    animal.describe();79}⋯
22animal.describe();⋯77for (Animal animal : animals) {78    animal.describe();79}⋯
23animal.describe();⋯77for (Animal animal : animals) {78    animal.describe();79}⋯
24System.out.println(" === Why Sealed Classes? ===");⋯81    System.out.println("\n=== Why Sealed Classes? ===");82    System.out.println("""83        1. CONTROL: Know exactly which classes extend yours84        2. SAFETY: Prevent unexpected subclasses85        3. EXHAUSTIVE: Switch can cover all cases86        4. DOCUMENTATION: Permits list shows intent87        88        Without sealed:89        - Anyone can extend your class90        - Switch might miss cases91        - Library users could break assumptions92        93        With sealed:94        - Only permitted classes can extend95        - Compiler knows all subclasses96        - Pattern matching is exhaustive97        """);98    99    System.out.println("=== Sealed Class Rules ===");100    System.out.println("""101        1. Use 'sealed' modifier on class102        2. Use 'permits' to list allowed subclasses103        3. Each permitted class must:104           - Be in same module (or package if unnamed)105           - Directly extend the sealed class106           - Be 'final', 'sealed', or 'non-sealed'107        """);108}⋯output
=== Why Sealed Classes? ===
1. CONTROL: Know exactly which classes extend yours
2. SAFETY: Prevent unexpected subclasses
3. EXHAUSTIVE: Switch can cover all cases
4. DOCUMENTATION: Permits list shows intent

Without sealed:
- Anyone can extend your class
- Switch might miss cases
- Library users could break assumptions

With sealed:
- Only permitted classes can extend
- Compiler knows all subclasses
- Pattern matching is exhaustive
=== Sealed Class Rules ===
1. Use 'sealed' modifier on class
2. Use 'permits' to list allowed subclasses
3. Each permitted class must:
   - Be in same module (or package if unnamed)
   - Directly extend the sealed class
   - Be 'final', 'sealed', or 'non-sealed'

All 3 passes — pass 1 is the card above
pass	`name`	`this.name`
1	Buddy	Buddy
2	Whiskers	Whiskers
3	Tweety	Tweety

All 6 passes — pass 1 is the card above
pass	`name`
1	Buddy
2	Whiskers
3	Tweety
4	Buddy
5	Whiskers
6	Tweety

All 3 passes — pass 1 is the card above
pass	`name`
1	Buddy
2	Whiskers
3	Tweety

All 3 passes — pass 1 is the card above
pass	`animal`
1	⟨Dog A⟩
2	⟨Cat B⟩
3	⟨Bird C⟩

sealed class X permits A, B, C - only A, B, C can extend X.

sealed Restricts subclasses to explicitly permitted list.

Permitted subclass options

Subclasses must be final, sealed, or non-sealed.

                            PermitsOptions.java
                        
Replay: real traced execution (multi-file project)

                            // Three Options for Permitted Subclasses

// Sealed parent
sealed class Vehicle permits Car, Motorcycle, Truck {
    private String brand;

    Vehicle(String brand) {
        this.brand = brand;
    }

    public String getBrand() {
        return brand;
    }
}

// Option 1: FINAL - cannot be extended
final class Motorcycle extends Vehicle {
    Motorcycle(String brand) {
        super(brand);
    }

    public void wheelie() {
        System.out.println(getBrand() + " motorcycle doing a wheelie!");
    }
}
// class SportBike extends Motorcycle { }  // ERROR! Motorcycle is final

// Option 2: SEALED - must specify own permits
sealed class Car extends Vehicle permits Sedan, SUV, SportsCar {
    Car(String brand) {
        super(brand);
    }

    public void honk() {
        System.out.println(getBrand() + " car: Beep beep!");
    }
}

// Car's permitted subclasses must also choose
final class Sedan extends Car {
    Sedan(String brand) {
        super(brand);
    }
}

final class SUV extends Car {
    SUV(String brand) {
        super(brand);
    }
}

final class SportsCar extends Car {
    SportsCar(String brand) {
        super(brand);
    }
}

// Option 3: NON-SEALED - open for anyone
non-sealed class Truck extends Vehicle {
    Truck(String brand) {
        super(brand);
    }

    public void loadCargo() {
        System.out.println(getBrand() + " truck loading cargo");
    }
}

// Anyone can extend non-sealed!
class PickupTruck extends Truck {
    PickupTruck(String brand) {
        super(brand);
    }
}

class SemiTruck extends Truck {
    SemiTruck(String brand) {
        super(brand);
    }
}

// Even more levels!
class MonsterTruck extends PickupTruck {
    MonsterTruck(String brand) {
        super(brand);
    }
}

public class PermitsOptions {
    public static void main(String[] args) {
        System.out.println("=== Three Options for Permitted Classes ===\n");

        System.out.println("1. FINAL (Motorcycle):");
        Motorcycle harley = new Motorcycle("Harley");
        harley.wheelie();
        // Cannot create subclass of Motorcycle

        System.out.println("\n2. SEALED (Car):");
        Sedan toyota = new Sedan("Toyota");
        SUV jeep = new SUV("Jeep");
        SportsCar porsche = new SportsCar("Porsche");
        toyota.honk();
        jeep.honk();
        porsche.honk();
        // Car hierarchy is closed: only Sedan, SUV, SportsCar

        System.out.println("\n3. NON-SEALED (Truck):");
        Truck ford = new Truck("Ford");
        PickupTruck pickup = new PickupTruck("Chevrolet");
        SemiTruck semi = new SemiTruck("Peterbilt");
        MonsterTruck monster = new MonsterTruck("BigFoot");
        ford.loadCargo();
        pickup.loadCargo();
        semi.loadCargo();
        monster.loadCargo();
        // Truck hierarchy is open - anyone can extend

        System.out.println("\n=== Hierarchy Summary ===");
        System.out.println("""
            Vehicle (sealed)
            ├── Motorcycle (final)
            │   └── [closed - no subclasses]
            │
            ├── Car (sealed)
            │   ├── Sedan (final)
            │   ├── SUV (final)
            │   └── SportsCar (final)
            │
            └── Truck (non-sealed)
                ├── PickupTruck
                │   └── MonsterTruck
                └── SemiTruck
            """);

        System.out.println("=== When to Use Each ===");
        System.out.println("""
            FINAL:
            - Leaf classes in your hierarchy
            - No further specialization needed
            - Most restrictive

            SEALED:
            - Want to control next level too
            - Multi-level controlled hierarchy
            - Must list all permitted subclasses

            NON-SEALED:
            - Open extension point
            - Let users extend your class
            - Escape hatch from sealed hierarchy
            """);
    }
}

                        
1public static void main(String[] args)⋯89public class PermitsOptions {90    public static void main(String[] args) {91        System.out.println("=== Three Options for Permitted Classes ===\n");92        93        System.out.println("1. FINAL (Motorcycle):");94        Motorcycle harley = new Motorcycle("Harley");95        harley.wheelie();⋯output=== Three Options for Permitted Classes ===
1. FINAL (Motorcycle):
2this.brand ← Harleypass 1 of 8⋯7Vehicle(String brandHarley) {8    this.brand→ Harley = brandHarley;9}⋯All 8 passes — pass 1 is the card abovepassbrandthis.brand
1HarleyHarley
2ToyotaToyota
3JeepJeep
4PorschePorsche
5FordFord
6ChevroletChevrolet
7PeterbiltPeterbilt
8BigFootBigFoot
3Motorcycle(String brand)⋯17final class Motorcycle extends Vehicle { //?motorcyclefinal18    Motorcycle(String brandHarley) {19        super(brand);⋯
4harley ← ⟨Motorcycle A⟩⋯93System.out.println("1. FINAL (Motorcycle):");94Motorcycle harley→ ⟨Motorcycle A⟩ = new Motorcycle("Harley");95harley.wheelie();96// Cannot create subclass of Motorcycle⋯
5public String getBrand()pass 1 of 8⋯11public String getBrand() {12    return brandHarley;13}⋯All 8 passes — pass 1 is the card abovepassbrand
1Harley
2Toyota
3Jeep
4Porsche
5Ford
6Chevrolet
7Peterbilt
8BigFoot
6System.out.println(getBrand() + " motorcycle doing a wheelie!");⋯22public void wheelie() {23    System.out.println(getBrand() + " motorcycle doing a wheelie!");24}⋯outputHarley motorcycle doing a wheelie!
7harley.wheelie();⋯94Motorcycle harley = new Motorcycle("Harley");95harley.wheelie();96// Cannot create subclass of Motorcycle9798System.out.println("\n2. SEALED (Car):");99Sedan toyota = new Sedan("Toyota");100SUV jeep = new SUV("Jeep");⋯output
2. SEALED (Car):
8Car(String brand)pass 1 of 3⋯29sealed class Car extends Vehicle permits Sedan, SUV, SportsCar { //?carpermits30    Car(String brandToyota) {31        super(brand);⋯All 3 passes — pass 1 is the card abovepassbrand
1Toyota
2Jeep
3Porsche
9Sedan(String brand)⋯40final class Sedan extends Car { //?sedanfinal41    Sedan(String brandToyota) {42        super(brand);⋯
10toyota ← ⟨Sedan B⟩⋯98System.out.println("\n2. SEALED (Car):");99Sedan toyota→ ⟨Sedan B⟩ = new Sedan("Toyota");100SUV jeep = new SUV("Jeep");101SportsCar porsche = new SportsCar("Porsche");⋯
11SUV(String brand)⋯46final class SUV extends Car {47    SUV(String brandJeep) {48        super(brand);⋯
12jeep ← ⟨SUV C⟩⋯99Sedan toyota = new Sedan("Toyota");100SUV jeep→ ⟨SUV C⟩ = new SUV("Jeep");101SportsCar porsche = new SportsCar("Porsche");102toyota.honk();⋯
13SportsCar(String brand)⋯52final class SportsCar extends Car {53    SportsCar(String brandPorsche) {54        super(brand);⋯
14porsche ← ⟨SportsCar D⟩⋯100SUV jeep = new SUV("Jeep");101SportsCar porsche→ ⟨SportsCar D⟩ = new SportsCar("Porsche");102toyota.honk();103jeep.honk();⋯
15System.out.println(getBrand() + " car: Beep beep!");⋯34public void honk() {35    System.out.println(getBrand() + " car: Beep beep!");36}⋯outputToyota car: Beep beep!
16toyota.honk();⋯101SportsCar porsche = new SportsCar("Porsche");102toyota.honk();103jeep.honk();104porsche.honk();⋯
17System.out.println(getBrand() + " car: Beep beep!");⋯34public void honk() {35    System.out.println(getBrand() + " car: Beep beep!");36}⋯outputJeep car: Beep beep!
18jeep.honk();⋯102toyota.honk();103jeep.honk();104porsche.honk();105// Car hierarchy is closed: only Sedan, SUV, SportsCar⋯
19System.out.println(getBrand() + " car: Beep beep!");⋯34public void honk() {35    System.out.println(getBrand() + " car: Beep beep!");36}⋯outputPorsche car: Beep beep!
20porsche.honk();⋯103jeep.honk();104porsche.honk();105// Car hierarchy is closed: only Sedan, SUV, SportsCar106107System.out.println("\n3. NON-SEALED (Truck):");108Truck ford = new Truck("Ford");109PickupTruck pickup = new PickupTruck("Chevrolet");⋯output
3. NON-SEALED (Truck):
21Truck(String brand)pass 1 of 4⋯59non-sealed class Truck extends Vehicle { //?trucknonseal60    Truck(String brandFord) {61        super(brand);⋯All 4 passes — pass 1 is the card abovepassbrand
1Ford
2Chevrolet
3Peterbilt
4BigFoot
22ford ← ⟨Truck E⟩⋯107System.out.println("\n3. NON-SEALED (Truck):");108Truck ford→ ⟨Truck E⟩ = new Truck("Ford");109PickupTruck pickup = new PickupTruck("Chevrolet");110SemiTruck semi = new SemiTruck("Peterbilt");⋯
23PickupTruck(String brand)pass 1 of 2⋯70class PickupTruck extends Truck { //?pickup71    PickupTruck(String brandChevrolet) {72        super(brand);⋯
24pickup ← ⟨PickupTruck F⟩⋯108Truck ford = new Truck("Ford");109PickupTruck pickup→ ⟨PickupTruck F⟩ = new PickupTruck("Chevrolet");110SemiTruck semi = new SemiTruck("Peterbilt");111MonsterTruck monster = new MonsterTruck("BigFoot");⋯
25SemiTruck(String brand)⋯76class SemiTruck extends Truck { //?semi77    SemiTruck(String brandPeterbilt) {78        super(brand);⋯
26semi ← ⟨SemiTruck G⟩⋯109PickupTruck pickup = new PickupTruck("Chevrolet");110SemiTruck semi→ ⟨SemiTruck G⟩ = new SemiTruck("Peterbilt");111MonsterTruck monster = new MonsterTruck("BigFoot");112ford.loadCargo();⋯
27PickupTruck(String brand)pass 2 of 2⋯70class PickupTruck extends Truck { //?pickup71    PickupTruck(String brandBigFoot) {72        super(brand);⋯
28MonsterTruck(String brand)⋯83class MonsterTruck extends PickupTruck {84    MonsterTruck(String brandBigFoot) {85        super(brand);⋯
29monster ← ⟨MonsterTruck H⟩⋯110SemiTruck semi = new SemiTruck("Peterbilt");111MonsterTruck monster→ ⟨MonsterTruck H⟩ = new MonsterTruck("BigFoot");112ford.loadCargo();113pickup.loadCargo();⋯
30System.out.println(getBrand() + " truck loading cargo");⋯64public void loadCargo() {65    System.out.println(getBrand() + " truck loading cargo");66}⋯outputFord truck loading cargo
31ford.loadCargo();⋯111MonsterTruck monster = new MonsterTruck("BigFoot");112ford.loadCargo();113pickup.loadCargo();114semi.loadCargo();⋯
32System.out.println(getBrand() + " truck loading cargo");⋯64public void loadCargo() {65    System.out.println(getBrand() + " truck loading cargo");66}⋯outputChevrolet truck loading cargo
33pickup.loadCargo();⋯112ford.loadCargo();113pickup.loadCargo();114semi.loadCargo();115monster.loadCargo();⋯
34System.out.println(getBrand() + " truck loading cargo");⋯64public void loadCargo() {65    System.out.println(getBrand() + " truck loading cargo");66}⋯outputPeterbilt truck loading cargo
35semi.loadCargo();⋯113pickup.loadCargo();114semi.loadCargo();115monster.loadCargo();116// Truck hierarchy is open - anyone can extend⋯
36System.out.println(getBrand() + " truck loading cargo");⋯64public void loadCargo() {65    System.out.println(getBrand() + " truck loading cargo");66}⋯outputBigFoot truck loading cargo
37monster.loadCargo();⋯114    semi.loadCargo();115    monster.loadCargo();116    // Truck hierarchy is open - anyone can extend117    118    System.out.println("\n=== Hierarchy Summary ===");119    System.out.println("""120        Vehicle (sealed)121        ├── Motorcycle (final)122        │   └── [closed - no subclasses]123        │124        ├── Car (sealed)125        │   ├── Sedan (final)126        │   ├── SUV (final)127        │   └── SportsCar (final)128        │129        └── Truck (non-sealed)130            ├── PickupTruck131            │   └── MonsterTruck132            └── SemiTruck133        """);134    135    System.out.println("=== When to Use Each ===");136    System.out.println("""137        FINAL:138        - Leaf classes in your hierarchy139        - No further specialization needed140        - Most restrictive141        142        SEALED:143        - Want to control next level too144        - Multi-level controlled hierarchy145        - Must list all permitted subclasses146        147        NON-SEALED:148        - Open extension point149        - Let users extend your class150        - Escape hatch from sealed hierarchy151        """);152}⋯output
=== Hierarchy Summary ===
Vehicle (sealed)
├── Motorcycle (final)
│   └── [closed - no subclasses]
│
├── Car (sealed)
│   ├── Sedan (final)
│   ├── SUV (final)
│   └── SportsCar (final)
│
└── Truck (non-sealed)
    ├── PickupTruck
    │   └── MonsterTruck
    └── SemiTruck
=== When to Use Each ===
FINAL:
- Leaf classes in your hierarchy
- No further specialization needed
- Most restrictive

SEALED:
- Want to control next level too
- Multi-level controlled hierarchy
- Must list all permitted subclasses

NON-SEALED:
- Open extension point
- Let users extend your class
- Escape hatch from sealed hierarchy

All 8 passes — pass 1 is the card above
pass	`brand`	`this.brand`
1	Harley	Harley
2	Toyota	Toyota
3	Jeep	Jeep
4	Porsche	Porsche
5	Ford	Ford
6	Chevrolet	Chevrolet
7	Peterbilt	Peterbilt
8	BigFoot	BigFoot

All 8 passes — pass 1 is the card above
pass	`brand`
1	Harley
2	Toyota
3	Jeep
4	Porsche
5	Ford
6	Chevrolet
7	Peterbilt
8	BigFoot

All 3 passes — pass 1 is the card above
pass	`brand`
1	Toyota
2	Jeep
3	Porsche

All 4 passes — pass 1 is the card above
pass	`brand`
1	Ford
2	Chevrolet
3	Peterbilt
4	BigFoot

final = no more subclasses. sealed = controlled. non-sealed = open again.

permits Lists allowed subclasses: `permits Circle, Rectangle, Triangle`.

Sealed interfaces

Interfaces can be sealed too.

                            SealedInterfaces.java
                        
Replay: real traced execution (multi-file project)

                            // Sealed Interfaces

// Sealed interface - works same as sealed class
sealed interface Payment permits CreditCard, DebitCard, DigitalWallet, CreditCardPayment, PayPalPayment {
    String getPaymentMethod();
    boolean process(double amount);
}

// Permitted implementations must be final, sealed, or non-sealed

final class CreditCard implements Payment {
    private String cardNumber;
    private String expiry;

    CreditCard(String cardNumber, String expiry) {
        this.cardNumber = cardNumber;
        this.expiry = expiry;
    }

    @Override
    public String getPaymentMethod() {
        return "Credit Card ending in " + cardNumber.substring(cardNumber.length() - 4);
    }

    @Override
    public boolean process(double amount) {
        System.out.println("Processing $" + amount + " via credit card");
        return true;
    }
}

final class DebitCard implements Payment {
    private String cardNumber;
    private String pin;

    DebitCard(String cardNumber, String pin) {
        this.cardNumber = cardNumber;
        this.pin = pin;
    }

    @Override
    public String getPaymentMethod() {
        return "Debit Card ending in " + cardNumber.substring(cardNumber.length() - 4);
    }

    @Override
    public boolean process(double amount) {
        System.out.println("Processing $" + amount + " via debit card");
        return true;
    }
}

// Sealed implementation that permits further
sealed class DigitalWallet implements Payment permits PayPal, ApplePay, GooglePay {
    protected String accountId;

    DigitalWallet(String accountId) {
        this.accountId = accountId;
    }

    @Override
    public String getPaymentMethod() {
        return "Digital Wallet: " + accountId;
    }

    @Override
    public boolean process(double amount) {
        System.out.println("Processing $" + amount + " via digital wallet");
        return true;
    }
}

final class PayPal extends DigitalWallet {
    PayPal(String email) {
        super(email);
    }

    @Override
    public String getPaymentMethod() {
        return "PayPal: " + accountId;
    }
}

final class ApplePay extends DigitalWallet {
    ApplePay(String deviceId) {
        super(deviceId);
    }

    @Override
    public String getPaymentMethod() {
        return "Apple Pay: " + accountId;
    }
}

final class GooglePay extends DigitalWallet {
    GooglePay(String email) {
        super(email);
    }

    @Override
    public String getPaymentMethod() {
        return "Google Pay: " + accountId;
    }
}

// Multiple sealed interfaces
sealed interface Refundable permits CreditCardPayment, PayPalPayment {
    void refund(double amount);
}

// Class can implement multiple sealed interfaces
final class CreditCardPayment implements Payment, Refundable {
    private String cardNumber;

    CreditCardPayment(String cardNumber) {
        this.cardNumber = cardNumber;
    }

    @Override
    public String getPaymentMethod() {
        return "Credit Card: " + cardNumber;
    }

    @Override
    public boolean process(double amount) {
        System.out.println("Processing $" + amount);
        return true;
    }

    @Override
    public void refund(double amount) {
        System.out.println("Refunding $" + amount + " to credit card");
    }
}

final class PayPalPayment implements Payment, Refundable {
    private String email;

    PayPalPayment(String email) {
        this.email = email;
    }

    @Override
    public String getPaymentMethod() {
        return "PayPal: " + email;
    }

    @Override
    public boolean process(double amount) {
        System.out.println("Processing $" + amount + " via PayPal");
        return true;
    }

    @Override
    public void refund(double amount) {
        System.out.println("Refunding $" + amount + " to PayPal");
    }
}

public class SealedInterfaces {
    public static void main(String[] args) {
        System.out.println("=== Sealed Interfaces ===\n");

        Payment credit = new CreditCard("1234567890123456", "12/25");
        Payment debit = new DebitCard("9876543210987654", "1234");
        Payment wallet = new PayPal("user@example.com");

        System.out.println("--- Payment Methods ---");
        System.out.println(credit.getPaymentMethod());
        System.out.println(debit.getPaymentMethod());
        System.out.println(wallet.getPaymentMethod());

        System.out.println("\n--- Processing Payments ---");
        credit.process(99.99);
        debit.process(49.99);
        wallet.process(29.99);

        System.out.println("\n--- Digital Wallet Implementations ---");
        DigitalWallet paypal = new PayPal("john@example.com");
        DigitalWallet apple = new ApplePay("device-12345");
        DigitalWallet google = new GooglePay("jane@gmail.com");

        System.out.println(paypal.getPaymentMethod());
        System.out.println(apple.getPaymentMethod());
        System.out.println(google.getPaymentMethod());

        System.out.println("\n--- Multiple Sealed Interfaces ---");
        Refundable refundable = new CreditCardPayment("1111222233334444");
        refundable.refund(25.00);

        System.out.println("\n=== Hierarchy ===");
        System.out.println("""
            Payment (sealed interface)
            ├── CreditCard (final class)
            ├── DebitCard (final class)
            └── DigitalWallet (sealed class)
                ├── PayPal (final)
                ├── ApplePay (final)
                └── GooglePay (final)

            Refundable (sealed interface)
            ├── CreditCardPayment (final, also implements Payment)
            └── PayPalPayment (final, also implements Payment)
            """);
    }
}

                        
1public static void main(String[] args)⋯160public class SealedInterfaces {161    public static void main(String[] args) {162        System.out.println("=== Sealed Interfaces ===\n");163        164        Payment credit = new CreditCard("1234567890123456", "12/25");165        Payment debit = new DebitCard("9876543210987654", "1234");⋯output=== Sealed Interfaces ===
2this.cardNumber ← 1234567890123456, this.expiry ← 12/25⋯15CreditCard(String cardNumber1234567890123456, String expiry12/25) {16    this.cardNumber→ 1234567890123456 = cardNumber1234567890123456;17    this.expiry→ 12/25 = expiry12/25;18}⋯
3credit ← ⟨CreditCard A⟩⋯164Payment credit→ ⟨CreditCard A⟩ = new CreditCard("1234567890123456", "12/25");165Payment debit = new DebitCard("9876543210987654", "1234");166Payment wallet = new PayPal("user@example.com");⋯
4this.cardNumber ← 9876543210987654, this.pin ← 1234⋯36DebitCard(String cardNumber9876543210987654, String pin1234) {37    this.cardNumber→ 9876543210987654 = cardNumber9876543210987654;38    this.pin→ 1234 = pin1234;39}⋯
5debit ← ⟨DebitCard B⟩⋯164Payment credit = new CreditCard("1234567890123456", "12/25");165Payment debit→ ⟨DebitCard B⟩ = new DebitCard("9876543210987654", "1234");166Payment wallet = new PayPal("user@example.com");⋯
6this.accountId ← user@example.compass 1 of 4⋯57DigitalWallet(String accountIduser@example.com) {58    this.accountId→ user@example.com = accountIduser@example.com;59}⋯All 4 passes — pass 1 is the card abovepassaccountIdemaildeviceIdthis.accountId
1user@example.comuser@example.com—user@example.com
2john@example.comjohn@example.com—john@example.com
3device-12345—device-12345device-12345
4jane@gmail.comjane@gmail.com—jane@gmail.com
7PayPal(String email)pass 1 of 2⋯73final class PayPal extends DigitalWallet { //?paypal74    PayPal(String emailuser@example.com) {75        super(email);⋯
8wallet ← ⟨PayPal C⟩⋯165Payment debit = new DebitCard("9876543210987654", "1234");166Payment wallet→ ⟨PayPal C⟩ = new PayPal("user@example.com");167168System.out.println("--- Payment Methods ---");169System.out.println(credit.getPaymentMethod());170System.out.println(debit.getPaymentMethod());⋯output--- Payment Methods ---
9System.out.println(credit.getPaymentMethod());⋯168System.out.println("--- Payment Methods ---");169System.out.println(credit.getPaymentMethod());170System.out.println(debit.getPaymentMethod());171System.out.println(wallet.getPaymentMethod());⋯outputCredit Card ending in 3456
10System.out.println(debit.getPaymentMethod());⋯169System.out.println(credit.getPaymentMethod());170System.out.println(debit.getPaymentMethod());171System.out.println(wallet.getPaymentMethod());⋯outputDebit Card ending in 7654
11@Override
    public String getPaymentMethod()pass 1 of 2⋯78@Override79public String getPaymentMethod() {80    return "PayPal: " + accountIduser@example.com;81}⋯
12System.out.println(wallet.getPaymentMethod());⋯170System.out.println(debit.getPaymentMethod());171System.out.println(wallet.getPaymentMethod());172173System.out.println("\n--- Processing Payments ---");174credit.process(99.99);175debit.process(49.99);⋯outputPayPal: user@example.com

--- Processing Payments ---
13@Override
    public boolean process(double amount)⋯25@Override26public boolean process(double amount99.99) {27    System.out.println("Processing $" + amount99.99 + " via credit card");28    return true;29}⋯outputProcessing $99.99 via credit card
14credit.process(99.99);⋯173System.out.println("\n--- Processing Payments ---");174credit.process(99.99);175debit.process(49.99);176wallet.process(29.99);⋯
15@Override
    public boolean process(double amount)⋯46@Override47public boolean process(double amount49.99) {48    System.out.println("Processing $" + amount49.99 + " via debit card");49    return true;50}⋯outputProcessing $49.99 via debit card
16debit.process(49.99);⋯174credit.process(99.99);175debit.process(49.99);176wallet.process(29.99);⋯
17@Override
    public boolean process(double amount)⋯66@Override67public boolean process(double amount29.99) {68    System.out.println("Processing $" + amount29.99 + " via digital wallet");69    return true;70}⋯outputProcessing $29.99 via digital wallet
18wallet.process(29.99);⋯175debit.process(49.99);176wallet.process(29.99);177178System.out.println("\n--- Digital Wallet Implementations ---");179DigitalWallet paypal = new PayPal("john@example.com");180DigitalWallet apple = new ApplePay("device-12345");⋯output
--- Digital Wallet Implementations ---
19PayPal(String email)pass 2 of 2⋯73final class PayPal extends DigitalWallet { //?paypal74    PayPal(String emailjohn@example.com) {75        super(email);⋯
20paypal ← ⟨PayPal D⟩⋯178System.out.println("\n--- Digital Wallet Implementations ---");179DigitalWallet paypal→ ⟨PayPal D⟩ = new PayPal("john@example.com");180DigitalWallet apple = new ApplePay("device-12345");181DigitalWallet google = new GooglePay("jane@gmail.com");⋯
21ApplePay(String deviceId)⋯84final class ApplePay extends DigitalWallet { //?applepay85    ApplePay(String deviceIddevice-12345) {86        super(deviceId);⋯
22apple ← ⟨ApplePay E⟩⋯179DigitalWallet paypal = new PayPal("john@example.com");180DigitalWallet apple→ ⟨ApplePay E⟩ = new ApplePay("device-12345");181DigitalWallet google = new GooglePay("jane@gmail.com");⋯
23GooglePay(String email)⋯95final class GooglePay extends DigitalWallet {96    GooglePay(String emailjane@gmail.com) {97        super(email);⋯
24google ← ⟨GooglePay F⟩⋯180DigitalWallet apple = new ApplePay("device-12345");181DigitalWallet google→ ⟨GooglePay F⟩ = new GooglePay("jane@gmail.com");182183System.out.println(paypal.getPaymentMethod());184System.out.println(apple.getPaymentMethod());⋯
25@Override
    public String getPaymentMethod()pass 2 of 2⋯78@Override79public String getPaymentMethod() {80    return "PayPal: " + accountIdjohn@example.com;81}⋯
26System.out.println(paypal.getPaymentMethod());⋯183System.out.println(paypal.getPaymentMethod());184System.out.println(apple.getPaymentMethod());185System.out.println(google.getPaymentMethod());⋯outputPayPal: john@example.com
27@Override
    public String getPaymentMethod()⋯89@Override90public String getPaymentMethod() {91    return "Apple Pay: " + accountIddevice-12345;92}⋯
28System.out.println(apple.getPaymentMethod());⋯183System.out.println(paypal.getPaymentMethod());184System.out.println(apple.getPaymentMethod());185System.out.println(google.getPaymentMethod());⋯outputApple Pay: device-12345
29@Override
    public String getPaymentMethod()⋯100@Override101public String getPaymentMethod() {102    return "Google Pay: " + accountIdjane@gmail.com;103}⋯
30System.out.println(google.getPaymentMethod());⋯184System.out.println(apple.getPaymentMethod());185System.out.println(google.getPaymentMethod());186187System.out.println("\n--- Multiple Sealed Interfaces ---");188Refundable refundable = new CreditCardPayment("1111222233334444");189refundable.refund(25.00);⋯outputGoogle Pay: jane@gmail.com

--- Multiple Sealed Interfaces ---
31this.cardNumber ← 1111222233334444⋯115CreditCardPayment(String cardNumber1111222233334444) {116    this.cardNumber→ 1111222233334444 = cardNumber1111222233334444;117}⋯
32refundable ← ⟨CreditCardPayment G⟩⋯187System.out.println("\n--- Multiple Sealed Interfaces ---");188Refundable refundable→ ⟨CreditCardPayment G⟩ = new CreditCardPayment("1111222233334444");189refundable.refund(25.00);⋯
33@Override
    public void refund(double amount)⋯130@Override131public void refund(double amount25.0) {132    System.out.println("Refunding $" + amount25.0 + " to credit card");133}⋯outputRefunding $25.0 to credit card
34refundable.refund(25.00);⋯188    Refundable refundable = new CreditCardPayment("1111222233334444");189    refundable.refund(25.00);190    191    System.out.println("\n=== Hierarchy ===");192    System.out.println("""193        Payment (sealed interface)194        ├── CreditCard (final class)195        ├── DebitCard (final class)196        └── DigitalWallet (sealed class)197            ├── PayPal (final)198            ├── ApplePay (final)199            └── GooglePay (final)200        201        Refundable (sealed interface)202        ├── CreditCardPayment (final, also implements Payment)203        └── PayPalPayment (final, also implements Payment)204        """);205}⋯output
=== Hierarchy ===
Payment (sealed interface)
├── CreditCard (final class)
├── DebitCard (final class)
└── DigitalWallet (sealed class)
    ├── PayPal (final)
    ├── ApplePay (final)
    └── GooglePay (final)

Refundable (sealed interface)
├── CreditCardPayment (final, also implements Payment)
└── PayPalPayment (final, also implements Payment)

All 4 passes — pass 1 is the card above
pass	`accountId`	`email`	`deviceId`	`this.accountId`
1	user@example.com	user@example.com	—	user@example.com
2	john@example.com	john@example.com	—	john@example.com
3	device-12345	—	device-12345	device-12345
4	jane@gmail.com	jane@gmail.com	—	jane@gmail.com

sealed interface works the same way. Implementing classes must be permitted.

Pattern matching with sealed

Exhaustive switch - compiler knows all cases.

                            PatternMatching.java
                        
Replay: real traced execution (multi-file project)

                            // Pattern Matching with Sealed Classes

// Sealed hierarchy for expressions
sealed interface Expr permits Num, Add, Mul, Neg {
    // Evaluate the expression
    int eval();
}

// Permitted implementations

final class Num implements Expr {
    private final int value;

    Num(int value) {
        this.value = value;
    }

    public int getValue() {
        return value;
    }

    @Override
    public int eval() {
        return value;
    }

    @Override
    public String toString() {
        return String.valueOf(value);
    }
}

final class Add implements Expr {
    private final Expr left;
    private final Expr right;

    Add(Expr left, Expr right) {
        this.left = left;
        this.right = right;
    }

    public Expr getLeft() { return left; }
    public Expr getRight() { return right; }

    @Override
    public int eval() {
        return left.eval() + right.eval();
    }

    @Override
    public String toString() {
        return "(" + left + " + " + right + ")";
    }
}

final class Mul implements Expr {
    private final Expr left;
    private final Expr right;

    Mul(Expr left, Expr right) {
        this.left = left;
        this.right = right;
    }

    public Expr getLeft() { return left; }
    public Expr getRight() { return right; }

    @Override
    public int eval() {
        return left.eval() * right.eval();
    }

    @Override
    public String toString() {
        return "(" + left + " * " + right + ")";
    }
}

final class Neg implements Expr {
    private final Expr expr;

    Neg(Expr expr) {
        this.expr = expr;
    }

    public Expr getExpr() { return expr; }

    @Override
    public int eval() {
        return -expr.eval();
    }

    @Override
    public String toString() {
        return "(-" + expr + ")";
    }
}

public class PatternMatching {
    public static void main(String[] args) {
        System.out.println("=== Pattern Matching with Sealed Classes ===\n");

        // Build expressions
        Expr simple = new Num(42);
        Expr addition = new Add(new Num(10), new Num(20));
        Expr complex = new Mul(
            new Add(new Num(2), new Num(3)),
            new Neg(new Num(4))
        );  // (2 + 3) * (-4) = -20

        System.out.println("--- Evaluation ---");
        System.out.println(simple + " = " + simple.eval());
        System.out.println(addition + " = " + addition.eval());
        System.out.println(complex + " = " + complex.eval());

        // Pattern matching in switch - EXHAUSTIVE!
        System.out.println("\n--- Pattern Matching ---");
        describeExpr(simple);
        describeExpr(addition);
        describeExpr(complex);

        System.out.println("\n--- Transformation ---");
        Expr doubled = transform(addition);
        System.out.println("Original: " + addition + " = " + addition.eval());
        System.out.println("Doubled:  " + doubled + " = " + doubled.eval());

        System.out.println("\n=== Why Exhaustive Matters ===");
        System.out.println("""
            With sealed classes, the compiler KNOWS all subclasses.
            Switch can check if all cases are covered!

            If we add a new Expr type (e.g., Div):
            - Compiler shows error in every switch
            - Forces us to handle new case
            - No runtime surprises!
            """);
    }

    // Pattern matching with exhaustive switch
    static void describeExpr(Expr expr) {
        String description = switch (expr) {
            case Num n -> "Number: " + n.getValue();
            case Add a -> "Addition of " + a.getLeft() + " and " + a.getRight();
            case Mul m -> "Multiplication of " + m.getLeft() + " and " + m.getRight();
            case Neg n -> "Negation of " + n.getExpr();
            // No default needed! Compiler knows all cases covered
        };
        System.out.println(description);
    }

    // Transform expression using pattern matching
    static Expr transform(Expr expr) {
        return switch (expr) {
            case Num n -> new Num(n.getValue() * 2);  // Double numbers
            case Add a -> new Add(transform(a.getLeft()), transform(a.getRight()));
            case Mul m -> new Mul(transform(m.getLeft()), transform(m.getRight()));
            case Neg n -> new Neg(transform(n.getExpr()));
        };
    }

    // If we add guards
    static String evaluate(Expr expr) {
        return switch (expr) {
            case Num n when n.getValue() == 0 -> "Zero";
            case Num n when n.getValue() > 0 -> "Positive: " + n.getValue();
            case Num n -> "Negative: " + n.getValue();  // Must come last for Num
            case Add a -> "Sum: " + a.eval();
            case Mul m -> "Product: " + m.eval();
            case Neg n -> "Negated: " + n.eval();
        };
    }
}

                        
1public static void main(String[] args)⋯99public class PatternMatching {100    public static void main(String[] args) {101        System.out.println("=== Pattern Matching with Sealed Classes ===\n");102        103        // Build expressions //?buildexpr104        Expr simple = new Num(42);105        Expr addition = new Add(new Num(10), new Num(20));⋯output=== Pattern Matching with Sealed Classes ===
2this.value ← 42pass 1 of 8⋯14Num(int value42) {15    this.value→ 42 = value42;16}⋯All 8 passes — pass 1 is the card abovepassvalueexprleftrightthis.valuethis.exprthis.leftthis.right
142———42———
210———10———
320———20———
42———2———
53———3———
644(2 + 3)(-4)44(2 + 3)(-4)
720——2020———
840———40———
3simple ← 42⋯103// Build expressions //?buildexpr104Expr simple→ 42 = new Num(42);105Expr addition = new Add(new Num(10), new Num(20));106Expr complex = new Mul(⋯
4this.left ← 10, this.right ← 20pass 1 of 3⋯37Add(Expr left10, Expr right20) {38    this.left→ 10 = left10;39    this.right→ 20 = right20;40}⋯All 3 passes — pass 1 is the card abovepassleftrightexprthis.leftthis.rightthis.expr
11020—1020—
2234234
32040—2040—
5addition ← (10 + 20)⋯104Expr simple = new Num(42);105Expr addition→ (10 + 20) = new Add(new Num(10), new Num(20));106Expr complex = new Mul(107    new Add(new Num(2), new Num(3)),108    new Neg(new Num(4))109);  // (2 + 3) * (-4) = -20⋯
6this.expr ← 4⋯82Neg(Expr expr4) {83    this.expr→ 4 = expr4;84}⋯
7this.left ← (2 + 3), this.right ← (-4)⋯60Mul(Expr left(2 + 3), Expr right(-4)) {61    this.left→ (2 + 3) = left(2 + 3);62    this.right→ (-4) = right(-4);63}⋯
8complex ← ((2 + 3) * (-4))⋯105Expr addition = new Add(new Num(10), new Num(20));106Expr complex→ ((2 + 3) * (-4)) = new Mul(107    new Add(new Num(2), new Num(3)),108    new Neg(new Num(4))109);  // (2 + 3) * (-4) = -20110111System.out.println("--- Evaluation ---");112System.out.println(simple42 + " = " + simple.eval());113System.out.println(addition + " = " + addition.eval());⋯output--- Evaluation ---
9@Override
    public int eval()pass 1 of 10⋯22@Override23public int eval() {24    return value42;25}⋯All 10 passes — pass 1 is the card abovepassvalue
142
210
320
42
53
64
710
820
920
1040
10System.out.println(simple + " = " + simple.eval());⋯111System.out.println("--- Evaluation ---");112System.out.println(simple42 + " = " + simple.eval());113System.out.println(addition(10 + 20) + " = " + addition.eval());114System.out.println(complex + " = " + complex.eval());⋯output42 = 42
11System.out.println(addition + " = " + addition.eval());⋯112System.out.println(simple + " = " + simple.eval());113System.out.println(addition(10 + 20) + " = " + addition.eval());114System.out.println(complex((2 + 3) * (-4)) + " = " + complex.eval());⋯output(10 + 20) = 30
12System.out.println(complex + " = " + complex.eval());⋯113System.out.println(addition + " = " + addition.eval());114System.out.println(complex((2 + 3) * (-4)) + " = " + complex.eval());115116// Pattern matching in switch - EXHAUSTIVE! //?exhaustive117System.out.println("\n--- Pattern Matching ---");118describeExpr(simple42);119describeExpr(addition);⋯output((2 + 3) * (-4)) = -20

--- Pattern Matching ---
13static void describeExpr(Expr expr)pass 1 of 3⋯139// Pattern matching with exhaustive switch //?describemethod140static void describeExpr(Expr expr42) {141    String description = switch (expr) { //?patternswitch142        case Num n -> "Number: " + n.getValue(); //?numpattern143        case Add a -> "Addition of " + a.getLeft() + " and " + a.getRight(); //?addpattern144        case Mul m -> "Multiplication of " + m.getLeft() + " and " + m.getRight();145        case Neg n -> "Negation of " + n.getExpr();146        // No default needed! Compiler knows all cases covered //?nodefault147    };148    System.out.println(description);⋯All 3 passes — pass 1 is the card abovepassexprleftright
142——
2(10 + 20)1020
3((2 + 3) * (-4))(2 + 3)(-4)
14public int getValue()pass 1 of 3⋯18public int getValue() {19    return value42;20}⋯All 3 passes — pass 1 is the card abovepassvalueright
142—
21020
320—
15description ← Number: 42⋯117    System.out.println("\n--- Pattern Matching ---");118    describeExpr(simple42);119    describeExpr(addition(10 + 20));120    describeExpr(complex);121    122    System.out.println("\n--- Transformation ---");123    Expr doubled = transform(addition);124    System.out.println("Original: " + addition + " = " + addition.eval());125    System.out.println("Doubled:  " + doubled + " = " + doubled.eval());126    127    System.out.println("\n=== Why Exhaustive Matters ===");128    System.out.println("""129        With sealed classes, the compiler KNOWS all subclasses.130        Switch can check if all cases are covered!131        132        If we add a new Expr type (e.g., Div):133        - Compiler shows error in every switch134        - Forces us to handle new case135        - No runtime surprises!136        """);137}138139// Pattern matching with exhaustive switch //?describemethod140static void describeExpr(Expr expr) {141    String description→ Number: 42 = switch (expr) { //?patternswitch142        case Num n -> "Number: " + n.getValue(); //?numpattern143        case Add a -> "Addition of " + a.getLeft() + " and " + a.getRight(); //?addpattern144        case Mul m -> "Multiplication of " + m.getLeft() + " and " + m.getRight();145        case Neg n -> "Negation of " + n.getExpr();146        // No default needed! Compiler knows all cases covered //?nodefault147    };148    System.out.println(descriptionNumber: 42);149}⋯outputNumber: 42
16public Expr getLeft()pass 1 of 2⋯42public Expr getLeft() { return left10; }43public Expr getRight() { return right; }⋯
17public Expr getRight()pass 1 of 2⋯42public Expr getLeft() { return left; }43public Expr getRight() { return right20; }⋯
18description ← Addition of 10 and 20⋯118    describeExpr(simple);119    describeExpr(addition(10 + 20));120    describeExpr(complex((2 + 3) * (-4)));121    122    System.out.println("\n--- Transformation ---");123    Expr doubled = transform(addition);124    System.out.println("Original: " + addition + " = " + addition.eval());125    System.out.println("Doubled:  " + doubled + " = " + doubled.eval());126    127    System.out.println("\n=== Why Exhaustive Matters ===");128    System.out.println("""129        With sealed classes, the compiler KNOWS all subclasses.130        Switch can check if all cases are covered!131        132        If we add a new Expr type (e.g., Div):133        - Compiler shows error in every switch134        - Forces us to handle new case135        - No runtime surprises!136        """);137}138139// Pattern matching with exhaustive switch //?describemethod140static void describeExpr(Expr expr) {141    String description→ Addition of 10 and 20 = switch (expr) { //?patternswitch142        case Num n -> "Number: " + n.getValue(); //?numpattern143        case Add a -> "Addition of " + a.getLeft() + " and " + a.getRight(); //?addpattern144        case Mul m -> "Multiplication of " + m.getLeft() + " and " + m.getRight();145        case Neg n -> "Negation of " + n.getExpr();146        // No default needed! Compiler knows all cases covered //?nodefault147    };148    System.out.println(descriptionAddition of 10 and 20);149}⋯outputAddition of 10 and 20
19public Expr getLeft()⋯65public Expr getLeft() { return left(2 + 3); }66public Expr getRight() { return right; }⋯
20public Expr getRight()⋯65public Expr getLeft() { return left; }66public Expr getRight() { return right(-4); }⋯
21description ← Multiplication of (2 + 3) and (-4)⋯119    describeExpr(addition);120    describeExpr(complex((2 + 3) * (-4)));121    122    System.out.println("\n--- Transformation ---");123    Expr doubled = transform(addition(10 + 20));124    System.out.println("Original: " + addition + " = " + addition.eval());125    System.out.println("Doubled:  " + doubled + " = " + doubled.eval());126    127    System.out.println("\n=== Why Exhaustive Matters ===");128    System.out.println("""129        With sealed classes, the compiler KNOWS all subclasses.130        Switch can check if all cases are covered!131        132        If we add a new Expr type (e.g., Div):133        - Compiler shows error in every switch134        - Forces us to handle new case135        - No runtime surprises!136        """);137}138139// Pattern matching with exhaustive switch //?describemethod140static void describeExpr(Expr expr) {141    String description→ Multiplication of (2 + 3) and (-4) = switch (expr) { //?patternswitch142        case Num n -> "Number: " + n.getValue(); //?numpattern143        case Add a -> "Addition of " + a.getLeft() + " and " + a.getRight(); //?addpattern144        case Mul m -> "Multiplication of " + m.getLeft() + " and " + m.getRight();145        case Neg n -> "Negation of " + n.getExpr();146        // No default needed! Compiler knows all cases covered //?nodefault147    };148    System.out.println(descriptionMultiplication of (2 + 3) and (-4));149}⋯outputMultiplication of (2 + 3) and (-4)

--- Transformation ---
22static Expr transform(Expr expr)pass 1 of 3⋯151// Transform expression using pattern matching //?transformmethod152static Expr transform(Expr expr(10 + 20)) {153    return switch (expr) { //?transformswitch154        case Num n -> new Num(n.getValue() * 2);  // Double numbers155        case Add a -> new Add(transform(a.getLeft()), transform(a.getRight()));156        case Mul m -> new Mul(transform(m.getLeft()), transform(m.getRight()));157        case Neg n -> new Neg(transform(n.getExpr()));158    };159}⋯All 3 passes — pass 1 is the card abovepassexprleftright
1(10 + 20)10—
210—20
320——
23public Expr getLeft()pass 2 of 2⋯42public Expr getLeft() { return left10; }43public Expr getRight() { return right; }⋯
24public Expr getRight()pass 2 of 2⋯42public Expr getLeft() { return left; }43public Expr getRight() { return right20; }⋯
25doubled ← (20 + 40)⋯122System.out.println("\n--- Transformation ---");123Expr doubled→ (20 + 40) = transform(addition(10 + 20));124System.out.println("Original: " + addition(10 + 20) + " = " + addition.eval());125System.out.println("Doubled:  " + doubled + " = " + doubled.eval());⋯
26System.out.println("Original: " + addition + " = " + addition.eval());⋯123Expr doubled = transform(addition);124System.out.println("Original: " + addition(10 + 20) + " = " + addition.eval());125System.out.println("Doubled:  " + doubled(20 + 40) + " = " + doubled.eval());⋯outputOriginal: (10 + 20) = 30
27System.out.println("Doubled:  " + doubled + " = " + doubled.eval());⋯124    System.out.println("Original: " + addition + " = " + addition.eval());125    System.out.println("Doubled:  " + doubled(20 + 40) + " = " + doubled.eval());126    127    System.out.println("\n=== Why Exhaustive Matters ===");128    System.out.println("""129        With sealed classes, the compiler KNOWS all subclasses.130        Switch can check if all cases are covered!131        132        If we add a new Expr type (e.g., Div):133        - Compiler shows error in every switch134        - Forces us to handle new case135        - No runtime surprises!136        """);137}⋯outputDoubled:  (20 + 40) = 60

=== Why Exhaustive Matters ===
With sealed classes, the compiler KNOWS all subclasses.
Switch can check if all cases are covered!

If we add a new Expr type (e.g., Div):
- Compiler shows error in every switch
- Forces us to handle new case
- No runtime surprises!

All 8 passes — pass 1 is the card above
pass	`value`	`expr`	`left`	`right`	`this.value`	`this.expr`	`this.left`	`this.right`
1	42	—	—	—	42	—	—	—
2	10	—	—	—	10	—	—	—
3	20	—	—	—	20	—	—	—
4	2	—	—	—	2	—	—	—
5	3	—	—	—	3	—	—	—
6	4	4	(2 + 3)	(-4)	4	4	(2 + 3)	(-4)
7	20	—	—	20	20	—	—	—
8	40	—	—	—	40	—	—	—

All 3 passes — pass 1 is the card above
pass	`left`	`right`	`expr`	`this.left`	`this.right`	`this.expr`
1	10	20	—	10	20	—
2	2	3	4	2	3	4
3	20	40	—	20	40	—

All 10 passes — pass 1 is the card above
pass	`value`
1	42
2	10
3	20
4	2
5	3
6	4
7	10
8	20
9	20
10	40

All 3 passes — pass 1 is the card above
pass	`expr`	`left`	`right`
1	42	—	—
2	(10 + 20)	10	20
3	((2 + 3) * (-4))	(2 + 3)	(-4)

All 3 passes — pass 1 is the card above
pass	`value`	`right`
1	42	—
2	10	20
3	20	—

All 3 passes — pass 1 is the card above
pass	`expr`	`left`	`right`
1	(10 + 20)	10	—
2	10	—	20
3	20	—	—

Switch on sealed type is exhaustive - no default needed.

Records with sealed

Combine records and sealed for algebraic data types.

                            scaleFactor
                            scaleFactor = 2.0 (default)scaleFactor = 0.5scaleFactor = 3.0
                        

                            RecordsInSealed.java
                        
Replay: real traced execution (multi-file project)

                            // Records with Sealed Classes

// Sealed interface with record implementations
sealed interface Shape permits Circle, Rectangle, Triangle {
    double area();
    double perimeter();
}

// Records are implicitly final - perfect for sealed!
record Circle(double radius) implements Shape {
    @Override
    public double area() {
        return Math.PI * radius * radius;
    }

    @Override
    public double perimeter() {
        return 2 * Math.PI * radius;
    }
}

record Rectangle(double width, double height) implements Shape {
    @Override
    public double area() {
        return width * height;
    }

    @Override
    public double perimeter() {
        return 2 * (width + height);
    }
}

record Triangle(double a, double b, double c) implements Shape {
    // Compact constructor for validation
    public Triangle {
        if (a + b <= c || b + c <= a || a + c <= b) {
            throw new IllegalArgumentException("Invalid triangle sides");
        }
    }

    @Override
    public double area() {
        double s = (a + b + c) / 2;
        return Math.sqrt(s * (s - a) * (s - b) * (s - c));
    }

    @Override
    public double perimeter() {
        return a + b + c;
    }
}

// Pattern matching with record deconstruction
class ShapeProcessor {
    // Exhaustive switch with record patterns
    static String describe(Shape shape) {
        return switch (shape) {
            case Circle(var r) ->
                String.format("Circle with radius %.2f", r);
            case Rectangle(var w, var h) when w == h ->
                String.format("Square with side %.2f", w);
            case Rectangle(var w, var h) ->
                String.format("Rectangle %.2f x %.2f", w, h);
            case Triangle(var a, var b, var c) when a == b && b == c ->
                String.format("Equilateral triangle with side %.2f", a);
            case Triangle(var a, var b, var c) ->
                String.format("Triangle with sides %.2f, %.2f, %.2f", a, b, c);
        };
    }

    // Calculate total area
    static double totalArea(Shape... shapes) {
        double total = 0;
        for (Shape shape : shapes) {
            total += shape.area();
        }
        return total;
    }

    // Scale shape
    static Shape scale(Shape shape, double factor) {
        return switch (shape) {
            case Circle(var r) -> new Circle(r * factor);
            case Rectangle(var w, var h) -> new Rectangle(w * factor, h * factor);
            case Triangle(var a, var b, var c) -> new Triangle(a * factor, b * factor, c * factor);
        };
    }
}

// Result type using sealed + records
sealed interface Result<T> permits Success, Failure {
    boolean isSuccess();
}

record Success<T>(T value) implements Result<T> {
    @Override
    public boolean isSuccess() {
        return true;
    }
}

record Failure<T>(String error) implements Result<T> {
    @Override
    public boolean isSuccess() {
        return false;
    }
}

public class RecordsInSealed {
    public static void main(String[] args) {
        System.out.println("=== Records with Sealed Classes ===\n");

        // Create shapes using records
        Circle circle = new Circle(5);
        Rectangle rect = new Rectangle(4, 6);
        Rectangle square = new Rectangle(5, 5);
        Triangle equilateral = new Triangle(3, 3, 3);
        Triangle scalene = new Triangle(3, 4, 5);

        Shape[] shapes = {circle, rect, square, equilateral, scalene};

        System.out.println("--- Shape Descriptions ---");
        for (Shape shape : shapes) {
            System.out.println(ShapeProcessor.describe(shape));
            System.out.printf("  Area: %.2f, Perimeter: %.2f%n",
                shape.area(), shape.perimeter());
        }

        System.out.println("\n--- Total Area ---");
        System.out.printf("Total: %.2f%n", ShapeProcessor.totalArea(shapes));

        // Scaling
        System.out.println("\n--- Scaling ---");
        double scaleFactor = 2.0;
        Shape scaledCircle = ShapeProcessor.scale(circle, scaleFactor);
        System.out.println("Original: " + circle);
        System.out.println("Scaled " + scaleFactor + "x: " + scaledCircle);

        // Result type example
        System.out.println("\n--- Result Type ---");
        Result<Integer> success = new Success<>(42);
        Result<Integer> failure = new Failure<>("Division by zero");

        processResult(success);
        processResult(failure);

        System.out.println("\n=== Benefits ===");
        System.out.println("""
            Records + Sealed:
            1. Records are implicitly final (perfect for sealed permits)
            2. Record patterns enable deconstruction in switch
            3. Compact syntax for value objects
            4. Automatic equals/hashCode/toString
            5. Guards can add extra conditions

            Common patterns:
            - Shape hierarchies
            - Expression trees (AST)
            - Result/Either types
            - Event types
            - Command patterns
            """);
    }

    // Process result with pattern matching
    static void processResult(Result<Integer> result) {
        switch (result) {
            case Success<Integer>(var value) ->
                System.out.println("Success: " + value);
            case Failure<Integer>(var error) ->
                System.out.println("Failure: " + error);
        }
    }
}
// Records with Sealed Classes

// Sealed interface with record implementations
sealed interface Shape permits Circle, Rectangle, Triangle {
    double area();
    double perimeter();
}

// Records are implicitly final - perfect for sealed!
record Circle(double radius) implements Shape {
    @Override
    public double area() {
        return Math.PI * radius * radius;
    }

    @Override
    public double perimeter() {
        return 2 * Math.PI * radius;
    }
}

record Rectangle(double width, double height) implements Shape {
    @Override
    public double area() {
        return width * height;
    }

    @Override
    public double perimeter() {
        return 2 * (width + height);
    }
}

record Triangle(double a, double b, double c) implements Shape {
    // Compact constructor for validation
    public Triangle {
        if (a + b <= c || b + c <= a || a + c <= b) {
            throw new IllegalArgumentException("Invalid triangle sides");
        }
    }

    @Override
    public double area() {
        double s = (a + b + c) / 2;
        return Math.sqrt(s * (s - a) * (s - b) * (s - c));
    }

    @Override
    public double perimeter() {
        return a + b + c;
    }
}

// Pattern matching with record deconstruction
class ShapeProcessor {
    // Exhaustive switch with record patterns
    static String describe(Shape shape) {
        return switch (shape) {
            case Circle(var r) ->
                String.format("Circle with radius %.2f", r);
            case Rectangle(var w, var h) when w == h ->
                String.format("Square with side %.2f", w);
            case Rectangle(var w, var h) ->
                String.format("Rectangle %.2f x %.2f", w, h);
            case Triangle(var a, var b, var c) when a == b && b == c ->
                String.format("Equilateral triangle with side %.2f", a);
            case Triangle(var a, var b, var c) ->
                String.format("Triangle with sides %.2f, %.2f, %.2f", a, b, c);
        };
    }

    // Calculate total area
    static double totalArea(Shape... shapes) {
        double total = 0;
        for (Shape shape : shapes) {
            total += shape.area();
        }
        return total;
    }

    // Scale shape
    static Shape scale(Shape shape, double factor) {
        return switch (shape) {
            case Circle(var r) -> new Circle(r * factor);
            case Rectangle(var w, var h) -> new Rectangle(w * factor, h * factor);
            case Triangle(var a, var b, var c) -> new Triangle(a * factor, b * factor, c * factor);
        };
    }
}

// Result type using sealed + records
sealed interface Result<T> permits Success, Failure {
    boolean isSuccess();
}

record Success<T>(T value) implements Result<T> {
    @Override
    public boolean isSuccess() {
        return true;
    }
}

record Failure<T>(String error) implements Result<T> {
    @Override
    public boolean isSuccess() {
        return false;
    }
}

public class RecordsInSealed {
    public static void main(String[] args) {
        System.out.println("=== Records with Sealed Classes ===\n");

        // Create shapes using records
        Circle circle = new Circle(5);
        Rectangle rect = new Rectangle(4, 6);
        Rectangle square = new Rectangle(5, 5);
        Triangle equilateral = new Triangle(3, 3, 3);
        Triangle scalene = new Triangle(3, 4, 5);

        Shape[] shapes = {circle, rect, square, equilateral, scalene};

        System.out.println("--- Shape Descriptions ---");
        for (Shape shape : shapes) {
            System.out.println(ShapeProcessor.describe(shape));
            System.out.printf("  Area: %.2f, Perimeter: %.2f%n",
                shape.area(), shape.perimeter());
        }

        System.out.println("\n--- Total Area ---");
        System.out.printf("Total: %.2f%n", ShapeProcessor.totalArea(shapes));

        // Scaling
        System.out.println("\n--- Scaling ---");
        double scaleFactor = 0.5;
        Shape scaledCircle = ShapeProcessor.scale(circle, scaleFactor);
        System.out.println("Original: " + circle);
        System.out.println("Scaled " + scaleFactor + "x: " + scaledCircle);

        // Result type example
        System.out.println("\n--- Result Type ---");
        Result<Integer> success = new Success<>(42);
        Result<Integer> failure = new Failure<>("Division by zero");

        processResult(success);
        processResult(failure);

        System.out.println("\n=== Benefits ===");
        System.out.println("""
            Records + Sealed:
            1. Records are implicitly final (perfect for sealed permits)
            2. Record patterns enable deconstruction in switch
            3. Compact syntax for value objects
            4. Automatic equals/hashCode/toString
            5. Guards can add extra conditions

            Common patterns:
            - Shape hierarchies
            - Expression trees (AST)
            - Result/Either types
            - Event types
            - Command patterns
            """);
    }

    // Process result with pattern matching
    static void processResult(Result<Integer> result) {
        switch (result) {
            case Success<Integer>(var value) ->
                System.out.println("Success: " + value);
            case Failure<Integer>(var error) ->
                System.out.println("Failure: " + error);
        }
    }
}
// Records with Sealed Classes

// Sealed interface with record implementations
sealed interface Shape permits Circle, Rectangle, Triangle {
    double area();
    double perimeter();
}

// Records are implicitly final - perfect for sealed!
record Circle(double radius) implements Shape {
    @Override
    public double area() {
        return Math.PI * radius * radius;
    }

    @Override
    public double perimeter() {
        return 2 * Math.PI * radius;
    }
}

record Rectangle(double width, double height) implements Shape {
    @Override
    public double area() {
        return width * height;
    }

    @Override
    public double perimeter() {
        return 2 * (width + height);
    }
}

record Triangle(double a, double b, double c) implements Shape {
    // Compact constructor for validation
    public Triangle {
        if (a + b <= c || b + c <= a || a + c <= b) {
            throw new IllegalArgumentException("Invalid triangle sides");
        }
    }

    @Override
    public double area() {
        double s = (a + b + c) / 2;
        return Math.sqrt(s * (s - a) * (s - b) * (s - c));
    }

    @Override
    public double perimeter() {
        return a + b + c;
    }
}

// Pattern matching with record deconstruction
class ShapeProcessor {
    // Exhaustive switch with record patterns
    static String describe(Shape shape) {
        return switch (shape) {
            case Circle(var r) ->
                String.format("Circle with radius %.2f", r);
            case Rectangle(var w, var h) when w == h ->
                String.format("Square with side %.2f", w);
            case Rectangle(var w, var h) ->
                String.format("Rectangle %.2f x %.2f", w, h);
            case Triangle(var a, var b, var c) when a == b && b == c ->
                String.format("Equilateral triangle with side %.2f", a);
            case Triangle(var a, var b, var c) ->
                String.format("Triangle with sides %.2f, %.2f, %.2f", a, b, c);
        };
    }

    // Calculate total area
    static double totalArea(Shape... shapes) {
        double total = 0;
        for (Shape shape : shapes) {
            total += shape.area();
        }
        return total;
    }

    // Scale shape
    static Shape scale(Shape shape, double factor) {
        return switch (shape) {
            case Circle(var r) -> new Circle(r * factor);
            case Rectangle(var w, var h) -> new Rectangle(w * factor, h * factor);
            case Triangle(var a, var b, var c) -> new Triangle(a * factor, b * factor, c * factor);
        };
    }
}

// Result type using sealed + records
sealed interface Result<T> permits Success, Failure {
    boolean isSuccess();
}

record Success<T>(T value) implements Result<T> {
    @Override
    public boolean isSuccess() {
        return true;
    }
}

record Failure<T>(String error) implements Result<T> {
    @Override
    public boolean isSuccess() {
        return false;
    }
}

public class RecordsInSealed {
    public static void main(String[] args) {
        System.out.println("=== Records with Sealed Classes ===\n");

        // Create shapes using records
        Circle circle = new Circle(5);
        Rectangle rect = new Rectangle(4, 6);
        Rectangle square = new Rectangle(5, 5);
        Triangle equilateral = new Triangle(3, 3, 3);
        Triangle scalene = new Triangle(3, 4, 5);

        Shape[] shapes = {circle, rect, square, equilateral, scalene};

        System.out.println("--- Shape Descriptions ---");
        for (Shape shape : shapes) {
            System.out.println(ShapeProcessor.describe(shape));
            System.out.printf("  Area: %.2f, Perimeter: %.2f%n",
                shape.area(), shape.perimeter());
        }

        System.out.println("\n--- Total Area ---");
        System.out.printf("Total: %.2f%n", ShapeProcessor.totalArea(shapes));

        // Scaling
        System.out.println("\n--- Scaling ---");
        double scaleFactor = 3.0;
        Shape scaledCircle = ShapeProcessor.scale(circle, scaleFactor);
        System.out.println("Original: " + circle);
        System.out.println("Scaled " + scaleFactor + "x: " + scaledCircle);

        // Result type example
        System.out.println("\n--- Result Type ---");
        Result<Integer> success = new Success<>(42);
        Result<Integer> failure = new Failure<>("Division by zero");

        processResult(success);
        processResult(failure);

        System.out.println("\n=== Benefits ===");
        System.out.println("""
            Records + Sealed:
            1. Records are implicitly final (perfect for sealed permits)
            2. Record patterns enable deconstruction in switch
            3. Compact syntax for value objects
            4. Automatic equals/hashCode/toString
            5. Guards can add extra conditions

            Common patterns:
            - Shape hierarchies
            - Expression trees (AST)
            - Result/Either types
            - Event types
            - Command patterns
            """);
    }

    // Process result with pattern matching
    static void processResult(Result<Integer> result) {
        switch (result) {
            case Success<Integer>(var value) ->
                System.out.println("Success: " + value);
            case Failure<Integer>(var error) ->
                System.out.println("Failure: " + error);
        }
    }
}

                        
1circle ← Circle[radius=5.0], rect ← Rectangle[width=4.0, height=6.0]⋯110public class RecordsInSealed {111    public static void main(String[] args) {112        System.out.println("=== Records with Sealed Classes ===\n");113        114        // Create shapes using records //?createshapes115        Circle circle→ Circle[radius=5.0] = new Circle(5);116        Rectangle rect→ Rectangle[width=4.0, height=6.0] = new Rectangle(4, 6);117        Rectangle square→ Rectangle[width=5.0, height=5.0] = new Rectangle(5, 5);118        Triangle equilateral = new Triangle(3, 3, 3);119        Triangle scalene = new Triangle(3, 4, 5);⋯output=== Records with Sealed Classes ===
2equilateral ← Triangle[a=3.0, b=3.0, c=3.0]⋯117Rectangle square = new Rectangle(5, 5);118Triangle equilateral→ Triangle[a=3.0, b=3.0, c=3.0] = new Triangle(3, 3, 3);119Triangle scalene = new Triangle(3, 4, 5);⋯
3scalene ← Triangle[a=3.0, b=4.0, c=5.0]⋯118Triangle equilateral = new Triangle(3, 3, 3);119Triangle scalene→ Triangle[a=3.0, b=4.0, c=5.0] = new Triangle(3, 4, 5);120121Shape[] shapes = {circle, rect, square, equilateral, scalene};122123System.out.println("--- Shape Descriptions ---");124for (Shape shape : shapes) {⋯output--- Shape Descriptions ---
4for (Shape shape : shapes)pass 1 of 5⋯123System.out.println("--- Shape Descriptions ---");124for (Shape shapeCircle[radius=5.0] : shapes) {125    System.out.println(ShapeProcessor.describe(shapeCircle[radius=5.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", ⋯All 5 passes — pass 1 is the card abovepassshape
1Circle[radius=5.0]
2Rectangle[width=4.0, height=6.0]
3Rectangle[width=5.0, height=5.0]
4Triangle[a=3.0, b=3.0, c=3.0]
5Triangle[a=3.0, b=4.0, c=5.0]
5static String describe(Shape shape)pass 1 of 5⋯56// Exhaustive switch with record patterns //?recordpatterns57static String describe(Shape shapeCircle[radius=5.0]) {58    return switch (shape) {59        case Circle(var r) -> //?circlepattern60            String.format("Circle with radius %.2f", r);61        case Rectangle(var w, var h) when w == h -> //?squarepattern62            String.format("Square with side %.2f", w);63        case Rectangle(var w, var h) -> //?rectpattern64            String.format("Rectangle %.2f x %.2f", w, h);65        case Triangle(var a, var b, var c) when a == b && b == c -> //?equilateral66            String.format("Equilateral triangle with side %.2f", a);67        case Triangle(var a, var b, var c) -> //?anytrianglepattern68            String.format("Triangle with sides %.2f, %.2f, %.2f", a, b, c);69    };70}⋯All 5 passes — pass 1 is the card abovepassshape
1Circle[radius=5.0]
2Rectangle[width=4.0, height=6.0]
3Rectangle[width=5.0, height=5.0]
4Triangle[a=3.0, b=3.0, c=3.0]
5Triangle[a=3.0, b=4.0, c=5.0]
6System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeCircle[radius=5.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputCircle with radius 5.00
7@Override
    public double area()pass 1 of 2⋯10record Circle(double radius) implements Shape { //?circlerecord11    @Override12    public double area() {13        return Math.PI * radius5.0 * radius;14    }⋯
8@Override
    public double perimeter()⋯16@Override17public double perimeter() {18    return 2 * Math.PI * radius5.0;19}⋯
9System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
10System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeRectangle[width=4.0, height=6.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputRectangle 4.00 x 6.00
11@Override
    public double area()pass 1 of 4⋯22record Rectangle(double width, double height) implements Shape { //?rectanglerecord23    @Override24    public double area() {25        return width4.0 * height6.0;26    }⋯All 4 passes — pass 1 is the card abovepasswidthheight
14.06.0
25.05.0
34.06.0
45.05.0
12@Override
    public double perimeter()pass 1 of 2⋯28@Override29public double perimeter() {30    return 2 * (width4.0 + height6.0);31}⋯
13System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
14System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeRectangle[width=5.0, height=5.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputSquare with side 5.00
15@Override
    public double perimeter()pass 2 of 2⋯28@Override29public double perimeter() {30    return 2 * (width5.0 + height5.0);31}⋯
16System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
17System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeTriangle[a=3.0, b=3.0, c=3.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputEquilateral triangle with side 3.00
18s ← 4.5pass 1 of 4⋯42@Override43public double area() {44    double s→ 4.5 = (a3.0 + b3.0 + c3.0) / 2;45    return Math.sqrt(s4.5 * (s - a3.0) * (s - b3.0) * (s - c3.0));46}⋯All 4 passes — pass 1 is the card abovepassbcs
13.03.04.5
24.05.06.0
33.03.04.5
44.05.06.0
19@Override
    public double perimeter()pass 1 of 2⋯48@Override49public double perimeter() {50    return a3.0 + b3.0 + c3.0;51}⋯
20System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
21System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeTriangle[a=3.0, b=4.0, c=5.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputTriangle with sides 3.00, 4.00, 5.00
22@Override
    public double perimeter()pass 2 of 2⋯48@Override49public double perimeter() {50    return a3.0 + b4.0 + c5.0;51}⋯
23System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
24System.out.printf("Total: %.2f%n", ShapeProcessor.totalArea(shapes));⋯130System.out.println("\n--- Total Area ---");131System.out.printf("Total: %.2f%n", ShapeProcessor.totalArea(shapes));⋯output
--- Total Area ---
25total ← 0.0⋯72// Calculate total area //?totalarea73static double totalArea(Shape... shapes) {74    double total→ 0.0 = 0;75    for (Shape shape : shapes) {⋯
26for (Shape shape : shapes)pass 1 of 5⋯74double total = 0;75for (Shape shapeCircle[radius=5.0] : shapes) {76    total0.0 += shape.area();77}⋯All 5 passes — pass 1 is the card abovepassshapetotalradius
1Circle[radius=5.0]0.05.0
2Rectangle[width=4.0, height=6.0]78.53981633974483—
3Rectangle[width=5.0, height=5.0]102.53981633974483—
4Triangle[a=3.0, b=3.0, c=3.0]127.53981633974483—
5Triangle[a=3.0, b=4.0, c=5.0]131.4369306567748—
27@Override
    public double area()pass 2 of 2⋯10record Circle(double radius) implements Shape { //?circlerecord11    @Override12    public double area() {13        return Math.PI * radius5.0 * radius;14    }⋯
28total ← 78.53981633974483⋯75for (Shape shape : shapes) {76    total→ 78.53981633974483 += shape.area();77}⋯
29total ← 102.53981633974483⋯75for (Shape shape : shapes) {76    total→ 102.53981633974483 += shape.area();77}⋯
30total ← 127.53981633974483⋯75for (Shape shape : shapes) {76    total→ 127.53981633974483 += shape.area();77}⋯
31total ← 131.4369306567748⋯75for (Shape shape : shapes) {76    total→ 131.4369306567748 += shape.area();77}⋯
32total ← 137.4369306567748⋯75for (Shape shape : shapes) {76    total→ 137.4369306567748 += shape.area();77}⋯
33return total;⋯77    }78    return total137.4369306567748;79}⋯
34scaleFactor ← 2.0⋯130System.out.println("\n--- Total Area ---");131System.out.printf("Total: %.2f%n", ShapeProcessor.totalArea(shapes));132133// Scaling //?testscale134System.out.println("\n--- Scaling ---");135double scaleFactor→ 2.0 = 2.0;  //@scaleFactor=2.0, 0.5, 3.0136Shape scaledCircle = ShapeProcessor.scale(circleCircle[radius=5.0], scaleFactor2.0);137System.out.println("Original: " + circle);⋯output
--- Scaling ---
35static Shape scale(Shape shape, double factor)⋯81// Scale shape //?scale82static Shape scale(Shape shapeCircle[radius=5.0], double factor2.0) {83    return switch (shape) {84        case Circle(var r) -> new Circle(r * factor);85        case Rectangle(var w, var h) -> new Rectangle(w * factor, h * factor);86        case Triangle(var a, var b, var c) -> new Triangle(a * factor, b * factor, c * factor);87    };88}⋯
36scaledCircle ← Circle[radius=10.0], success ← Success[value=42]⋯135double scaleFactor = 2.0;  //@scaleFactor=2.0, 0.5, 3.0136Shape scaledCircle→ Circle[radius=10.0] = ShapeProcessor.scale(circleCircle[radius=5.0], scaleFactor2.0);137System.out.println("Original: " + circleCircle[radius=5.0]);138System.out.println("Scaled " + scaleFactor2.0 + "x: " + scaledCircleCircle[radius=10.0]);139140// Result type example //?testresult141System.out.println("\n--- Result Type ---");142Result<Integer> success→ Success[value=42] = new Success<>(42);143Result<Integer> failure→ Failure[error=Division by zero] = new Failure<>("Division by zero");144145processResult(successSuccess[value=42]);146processResult(failure);⋯outputOriginal: Circle[radius=5.0]
Scaled 2.0x: Circle[radius=10.0]

--- Result Type ---
37static void processResult(Result<Integer> result)pass 1 of 2⋯145    processResult(successSuccess[value=42]);146    processResult(failureFailure[error=Division by zero]);147    148    System.out.println("\n=== Benefits ===");149    System.out.println("""150        Records + Sealed:151        1. Records are implicitly final (perfect for sealed permits)152        2. Record patterns enable deconstruction in switch153        3. Compact syntax for value objects154        4. Automatic equals/hashCode/toString155        5. Guards can add extra conditions156        157        Common patterns:158        - Shape hierarchies159        - Expression trees (AST)160        - Result/Either types161        - Event types162        - Command patterns163        """);164}165166// Process result with pattern matching //?processresult167static void processResult(Result<Integer> resultSuccess[value=42]) {168    switch (result) {⋯
38static void processResult(Result<Integer> result)pass 2 of 2⋯145    processResult(success);146    processResult(failureFailure[error=Division by zero]);147    148    System.out.println("\n=== Benefits ===");149    System.out.println("""150        Records + Sealed:151        1. Records are implicitly final (perfect for sealed permits)152        2. Record patterns enable deconstruction in switch153        3. Compact syntax for value objects154        4. Automatic equals/hashCode/toString155        5. Guards can add extra conditions156        157        Common patterns:158        - Shape hierarchies159        - Expression trees (AST)160        - Result/Either types161        - Event types162        - Command patterns163        """);164}165166// Process result with pattern matching //?processresult167static void processResult(Result<Integer> resultFailure[error=Division by zero]) {168    switch (result) {⋯output
=== Benefits ===
Records + Sealed:
1. Records are implicitly final (perfect for sealed permits)
2. Record patterns enable deconstruction in switch
3. Compact syntax for value objects
4. Automatic equals/hashCode/toString
5. Guards can add extra conditions

Common patterns:
- Shape hierarchies
- Expression trees (AST)
- Result/Either types
- Event types
- Command patterns
1circle ← Circle[radius=5.0], rect ← Rectangle[width=4.0, height=6.0]⋯110public class RecordsInSealed {111    public static void main(String[] args) {112        System.out.println("=== Records with Sealed Classes ===\n");113        114        // Create shapes using records115        Circle circle→ Circle[radius=5.0] = new Circle(5);116        Rectangle rect→ Rectangle[width=4.0, height=6.0] = new Rectangle(4, 6);117        Rectangle square→ Rectangle[width=5.0, height=5.0] = new Rectangle(5, 5);118        Triangle equilateral = new Triangle(3, 3, 3);119        Triangle scalene = new Triangle(3, 4, 5);⋯output=== Records with Sealed Classes ===
2equilateral ← Triangle[a=3.0, b=3.0, c=3.0]⋯117Rectangle square = new Rectangle(5, 5);118Triangle equilateral→ Triangle[a=3.0, b=3.0, c=3.0] = new Triangle(3, 3, 3);119Triangle scalene = new Triangle(3, 4, 5);⋯
3scalene ← Triangle[a=3.0, b=4.0, c=5.0]⋯118Triangle equilateral = new Triangle(3, 3, 3);119Triangle scalene→ Triangle[a=3.0, b=4.0, c=5.0] = new Triangle(3, 4, 5);120121Shape[] shapes = {circle, rect, square, equilateral, scalene};122123System.out.println("--- Shape Descriptions ---");124for (Shape shape : shapes) {⋯output--- Shape Descriptions ---
4for (Shape shape : shapes)pass 1 of 5⋯123System.out.println("--- Shape Descriptions ---");124for (Shape shapeCircle[radius=5.0] : shapes) {125    System.out.println(ShapeProcessor.describe(shapeCircle[radius=5.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", ⋯All 5 passes — pass 1 is the card abovepassshape
1Circle[radius=5.0]
2Rectangle[width=4.0, height=6.0]
3Rectangle[width=5.0, height=5.0]
4Triangle[a=3.0, b=3.0, c=3.0]
5Triangle[a=3.0, b=4.0, c=5.0]
5static String describe(Shape shape)pass 1 of 5⋯56// Exhaustive switch with record patterns57static String describe(Shape shapeCircle[radius=5.0]) {58    return switch (shape) {59        case Circle(var r) ->60            String.format("Circle with radius %.2f", r);61        case Rectangle(var w, var h) when w == h ->62            String.format("Square with side %.2f", w);63        case Rectangle(var w, var h) ->64            String.format("Rectangle %.2f x %.2f", w, h);65        case Triangle(var a, var b, var c) when a == b && b == c ->66            String.format("Equilateral triangle with side %.2f", a);67        case Triangle(var a, var b, var c) ->68            String.format("Triangle with sides %.2f, %.2f, %.2f", a, b, c);69    };70}⋯All 5 passes — pass 1 is the card abovepassshape
1Circle[radius=5.0]
2Rectangle[width=4.0, height=6.0]
3Rectangle[width=5.0, height=5.0]
4Triangle[a=3.0, b=3.0, c=3.0]
5Triangle[a=3.0, b=4.0, c=5.0]
6System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeCircle[radius=5.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputCircle with radius 5.00
7@Override
    public double area()pass 1 of 2⋯10record Circle(double radius) implements Shape {11    @Override12    public double area() {13        return Math.PI * radius5.0 * radius;14    }⋯
8@Override
    public double perimeter()⋯16@Override17public double perimeter() {18    return 2 * Math.PI * radius5.0;19}⋯
9System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
10System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeRectangle[width=4.0, height=6.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputRectangle 4.00 x 6.00
11@Override
    public double area()pass 1 of 4⋯22record Rectangle(double width, double height) implements Shape {23    @Override24    public double area() {25        return width4.0 * height6.0;26    }⋯All 4 passes — pass 1 is the card abovepasswidthheight
14.06.0
25.05.0
34.06.0
45.05.0
12@Override
    public double perimeter()pass 1 of 2⋯28@Override29public double perimeter() {30    return 2 * (width4.0 + height6.0);31}⋯
13System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
14System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeRectangle[width=5.0, height=5.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputSquare with side 5.00
15@Override
    public double perimeter()pass 2 of 2⋯28@Override29public double perimeter() {30    return 2 * (width5.0 + height5.0);31}⋯
16System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
17System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeTriangle[a=3.0, b=3.0, c=3.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputEquilateral triangle with side 3.00
18s ← 4.5pass 1 of 4⋯42@Override43public double area() {44    double s→ 4.5 = (a3.0 + b3.0 + c3.0) / 2;45    return Math.sqrt(s4.5 * (s - a3.0) * (s - b3.0) * (s - c3.0));46}⋯All 4 passes — pass 1 is the card abovepassbcs
13.03.04.5
24.05.06.0
33.03.04.5
44.05.06.0
19@Override
    public double perimeter()pass 1 of 2⋯48@Override49public double perimeter() {50    return a3.0 + b3.0 + c3.0;51}⋯
20System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
21System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeTriangle[a=3.0, b=4.0, c=5.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputTriangle with sides 3.00, 4.00, 5.00
22@Override
    public double perimeter()pass 2 of 2⋯48@Override49public double perimeter() {50    return a3.0 + b4.0 + c5.0;51}⋯
23System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
24System.out.printf("Total: %.2f%n", ShapeProcessor.totalArea(shapes));⋯130System.out.println("\n--- Total Area ---");131System.out.printf("Total: %.2f%n", ShapeProcessor.totalArea(shapes));⋯output
--- Total Area ---
25total ← 0.0⋯72// Calculate total area73static double totalArea(Shape... shapes) {74    double total→ 0.0 = 0;75    for (Shape shape : shapes) {⋯
26for (Shape shape : shapes)pass 1 of 5⋯74double total = 0;75for (Shape shapeCircle[radius=5.0] : shapes) {76    total0.0 += shape.area();77}⋯All 5 passes — pass 1 is the card abovepassshapetotalradius
1Circle[radius=5.0]0.05.0
2Rectangle[width=4.0, height=6.0]78.53981633974483—
3Rectangle[width=5.0, height=5.0]102.53981633974483—
4Triangle[a=3.0, b=3.0, c=3.0]127.53981633974483—
5Triangle[a=3.0, b=4.0, c=5.0]131.4369306567748—
27@Override
    public double area()pass 2 of 2⋯10record Circle(double radius) implements Shape {11    @Override12    public double area() {13        return Math.PI * radius5.0 * radius;14    }⋯
28total ← 78.53981633974483⋯75for (Shape shape : shapes) {76    total→ 78.53981633974483 += shape.area();77}⋯
29total ← 102.53981633974483⋯75for (Shape shape : shapes) {76    total→ 102.53981633974483 += shape.area();77}⋯
30total ← 127.53981633974483⋯75for (Shape shape : shapes) {76    total→ 127.53981633974483 += shape.area();77}⋯
31total ← 131.4369306567748⋯75for (Shape shape : shapes) {76    total→ 131.4369306567748 += shape.area();77}⋯
32total ← 137.4369306567748⋯75for (Shape shape : shapes) {76    total→ 137.4369306567748 += shape.area();77}⋯
33return total;⋯77    }78    return total137.4369306567748;79}⋯
34scaleFactor ← 0.5⋯130System.out.println("\n--- Total Area ---");131System.out.printf("Total: %.2f%n", ShapeProcessor.totalArea(shapes));132133// Scaling134System.out.println("\n--- Scaling ---");135double scaleFactor→ 0.5 = 0.5;136Shape scaledCircle = ShapeProcessor.scale(circleCircle[radius=5.0], scaleFactor0.5);137System.out.println("Original: " + circle);⋯output
--- Scaling ---
35static Shape scale(Shape shape, double factor)⋯81// Scale shape82static Shape scale(Shape shapeCircle[radius=5.0], double factor0.5) {83    return switch (shape) {84        case Circle(var r) -> new Circle(r * factor);85        case Rectangle(var w, var h) -> new Rectangle(w * factor, h * factor);86        case Triangle(var a, var b, var c) -> new Triangle(a * factor, b * factor, c * factor);87    };88}⋯
36scaledCircle ← Circle[radius=2.5], success ← Success[value=42]⋯135double scaleFactor = 0.5;136Shape scaledCircle→ Circle[radius=2.5] = ShapeProcessor.scale(circleCircle[radius=5.0], scaleFactor0.5);137System.out.println("Original: " + circleCircle[radius=5.0]);138System.out.println("Scaled " + scaleFactor0.5 + "x: " + scaledCircleCircle[radius=2.5]);139140// Result type example141System.out.println("\n--- Result Type ---");142Result<Integer> success→ Success[value=42] = new Success<>(42);143Result<Integer> failure→ Failure[error=Division by zero] = new Failure<>("Division by zero");144145processResult(successSuccess[value=42]);146processResult(failure);⋯outputOriginal: Circle[radius=5.0]
Scaled 0.5x: Circle[radius=2.5]

--- Result Type ---
37static void processResult(Result<Integer> result)pass 1 of 2⋯145    processResult(successSuccess[value=42]);146    processResult(failureFailure[error=Division by zero]);147    148    System.out.println("\n=== Benefits ===");149    System.out.println("""150        Records + Sealed:151        1. Records are implicitly final (perfect for sealed permits)152        2. Record patterns enable deconstruction in switch153        3. Compact syntax for value objects154        4. Automatic equals/hashCode/toString155        5. Guards can add extra conditions156        157        Common patterns:158        - Shape hierarchies159        - Expression trees (AST)160        - Result/Either types161        - Event types162        - Command patterns163        """);164}165166// Process result with pattern matching167static void processResult(Result<Integer> resultSuccess[value=42]) {168    switch (result) {⋯
38static void processResult(Result<Integer> result)pass 2 of 2⋯145    processResult(success);146    processResult(failureFailure[error=Division by zero]);147    148    System.out.println("\n=== Benefits ===");149    System.out.println("""150        Records + Sealed:151        1. Records are implicitly final (perfect for sealed permits)152        2. Record patterns enable deconstruction in switch153        3. Compact syntax for value objects154        4. Automatic equals/hashCode/toString155        5. Guards can add extra conditions156        157        Common patterns:158        - Shape hierarchies159        - Expression trees (AST)160        - Result/Either types161        - Event types162        - Command patterns163        """);164}165166// Process result with pattern matching167static void processResult(Result<Integer> resultFailure[error=Division by zero]) {168    switch (result) {⋯output
=== Benefits ===
Records + Sealed:
1. Records are implicitly final (perfect for sealed permits)
2. Record patterns enable deconstruction in switch
3. Compact syntax for value objects
4. Automatic equals/hashCode/toString
5. Guards can add extra conditions

Common patterns:
- Shape hierarchies
- Expression trees (AST)
- Result/Either types
- Event types
- Command patterns
1circle ← Circle[radius=5.0], rect ← Rectangle[width=4.0, height=6.0]⋯110public class RecordsInSealed {111    public static void main(String[] args) {112        System.out.println("=== Records with Sealed Classes ===\n");113        114        // Create shapes using records115        Circle circle→ Circle[radius=5.0] = new Circle(5);116        Rectangle rect→ Rectangle[width=4.0, height=6.0] = new Rectangle(4, 6);117        Rectangle square→ Rectangle[width=5.0, height=5.0] = new Rectangle(5, 5);118        Triangle equilateral = new Triangle(3, 3, 3);119        Triangle scalene = new Triangle(3, 4, 5);⋯output=== Records with Sealed Classes ===
2equilateral ← Triangle[a=3.0, b=3.0, c=3.0]⋯117Rectangle square = new Rectangle(5, 5);118Triangle equilateral→ Triangle[a=3.0, b=3.0, c=3.0] = new Triangle(3, 3, 3);119Triangle scalene = new Triangle(3, 4, 5);⋯
3scalene ← Triangle[a=3.0, b=4.0, c=5.0]⋯118Triangle equilateral = new Triangle(3, 3, 3);119Triangle scalene→ Triangle[a=3.0, b=4.0, c=5.0] = new Triangle(3, 4, 5);120121Shape[] shapes = {circle, rect, square, equilateral, scalene};122123System.out.println("--- Shape Descriptions ---");124for (Shape shape : shapes) {⋯output--- Shape Descriptions ---
4for (Shape shape : shapes)pass 1 of 5⋯123System.out.println("--- Shape Descriptions ---");124for (Shape shapeCircle[radius=5.0] : shapes) {125    System.out.println(ShapeProcessor.describe(shapeCircle[radius=5.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", ⋯All 5 passes — pass 1 is the card abovepassshape
1Circle[radius=5.0]
2Rectangle[width=4.0, height=6.0]
3Rectangle[width=5.0, height=5.0]
4Triangle[a=3.0, b=3.0, c=3.0]
5Triangle[a=3.0, b=4.0, c=5.0]
5static String describe(Shape shape)pass 1 of 5⋯56// Exhaustive switch with record patterns57static String describe(Shape shapeCircle[radius=5.0]) {58    return switch (shape) {59        case Circle(var r) ->60            String.format("Circle with radius %.2f", r);61        case Rectangle(var w, var h) when w == h ->62            String.format("Square with side %.2f", w);63        case Rectangle(var w, var h) ->64            String.format("Rectangle %.2f x %.2f", w, h);65        case Triangle(var a, var b, var c) when a == b && b == c ->66            String.format("Equilateral triangle with side %.2f", a);67        case Triangle(var a, var b, var c) ->68            String.format("Triangle with sides %.2f, %.2f, %.2f", a, b, c);69    };70}⋯All 5 passes — pass 1 is the card abovepassshape
1Circle[radius=5.0]
2Rectangle[width=4.0, height=6.0]
3Rectangle[width=5.0, height=5.0]
4Triangle[a=3.0, b=3.0, c=3.0]
5Triangle[a=3.0, b=4.0, c=5.0]
6System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeCircle[radius=5.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputCircle with radius 5.00
7@Override
    public double area()pass 1 of 2⋯10record Circle(double radius) implements Shape {11    @Override12    public double area() {13        return Math.PI * radius5.0 * radius;14    }⋯
8@Override
    public double perimeter()⋯16@Override17public double perimeter() {18    return 2 * Math.PI * radius5.0;19}⋯
9System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
10System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeRectangle[width=4.0, height=6.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputRectangle 4.00 x 6.00
11@Override
    public double area()pass 1 of 4⋯22record Rectangle(double width, double height) implements Shape {23    @Override24    public double area() {25        return width4.0 * height6.0;26    }⋯All 4 passes — pass 1 is the card abovepasswidthheight
14.06.0
25.05.0
34.06.0
45.05.0
12@Override
    public double perimeter()pass 1 of 2⋯28@Override29public double perimeter() {30    return 2 * (width4.0 + height6.0);31}⋯
13System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
14System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeRectangle[width=5.0, height=5.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputSquare with side 5.00
15@Override
    public double perimeter()pass 2 of 2⋯28@Override29public double perimeter() {30    return 2 * (width5.0 + height5.0);31}⋯
16System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
17System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeTriangle[a=3.0, b=3.0, c=3.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputEquilateral triangle with side 3.00
18s ← 4.5pass 1 of 4⋯42@Override43public double area() {44    double s→ 4.5 = (a3.0 + b3.0 + c3.0) / 2;45    return Math.sqrt(s4.5 * (s - a3.0) * (s - b3.0) * (s - c3.0));46}⋯All 4 passes — pass 1 is the card abovepassbcs
13.03.04.5
24.05.06.0
33.03.04.5
44.05.06.0
19@Override
    public double perimeter()pass 1 of 2⋯48@Override49public double perimeter() {50    return a3.0 + b3.0 + c3.0;51}⋯
20System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
21System.out.println(ShapeProcessor.describe(shape));⋯124for (Shape shape : shapes) {125    System.out.println(ShapeProcessor.describe(shapeTriangle[a=3.0, b=4.0, c=5.0]));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯outputTriangle with sides 3.00, 4.00, 5.00
22@Override
    public double perimeter()pass 2 of 2⋯48@Override49public double perimeter() {50    return a3.0 + b4.0 + c5.0;51}⋯
23System.out.printf("  Area: %.2f, Perimeter: %.2f%n",⋯125    System.out.println(ShapeProcessor.describe(shape));126    System.out.printf("  Area: %.2f, Perimeter: %.2f%n", 127        shape.area(), shape.perimeter());128}⋯
24System.out.printf("Total: %.2f%n", ShapeProcessor.totalArea(shapes));⋯130System.out.println("\n--- Total Area ---");131System.out.printf("Total: %.2f%n", ShapeProcessor.totalArea(shapes));⋯output
--- Total Area ---
25total ← 0.0⋯72// Calculate total area73static double totalArea(Shape... shapes) {74    double total→ 0.0 = 0;75    for (Shape shape : shapes) {⋯
26for (Shape shape : shapes)pass 1 of 5⋯74double total = 0;75for (Shape shapeCircle[radius=5.0] : shapes) {76    total0.0 += shape.area();77}⋯All 5 passes — pass 1 is the card abovepassshapetotalradius
1Circle[radius=5.0]0.05.0
2Rectangle[width=4.0, height=6.0]78.53981633974483—
3Rectangle[width=5.0, height=5.0]102.53981633974483—
4Triangle[a=3.0, b=3.0, c=3.0]127.53981633974483—
5Triangle[a=3.0, b=4.0, c=5.0]131.4369306567748—
27@Override
    public double area()pass 2 of 2⋯10record Circle(double radius) implements Shape {11    @Override12    public double area() {13        return Math.PI * radius5.0 * radius;14    }⋯
28total ← 78.53981633974483⋯75for (Shape shape : shapes) {76    total→ 78.53981633974483 += shape.area();77}⋯
29total ← 102.53981633974483⋯75for (Shape shape : shapes) {76    total→ 102.53981633974483 += shape.area();77}⋯
30total ← 127.53981633974483⋯75for (Shape shape : shapes) {76    total→ 127.53981633974483 += shape.area();77}⋯
31total ← 131.4369306567748⋯75for (Shape shape : shapes) {76    total→ 131.4369306567748 += shape.area();77}⋯
32total ← 137.4369306567748⋯75for (Shape shape : shapes) {76    total→ 137.4369306567748 += shape.area();77}⋯
33return total;⋯77    }78    return total137.4369306567748;79}⋯
34scaleFactor ← 3.0⋯130System.out.println("\n--- Total Area ---");131System.out.printf("Total: %.2f%n", ShapeProcessor.totalArea(shapes));132133// Scaling134System.out.println("\n--- Scaling ---");135double scaleFactor→ 3.0 = 3.0;136Shape scaledCircle = ShapeProcessor.scale(circleCircle[radius=5.0], scaleFactor3.0);137System.out.println("Original: " + circle);⋯output
--- Scaling ---
35static Shape scale(Shape shape, double factor)⋯81// Scale shape82static Shape scale(Shape shapeCircle[radius=5.0], double factor3.0) {83    return switch (shape) {84        case Circle(var r) -> new Circle(r * factor);85        case Rectangle(var w, var h) -> new Rectangle(w * factor, h * factor);86        case Triangle(var a, var b, var c) -> new Triangle(a * factor, b * factor, c * factor);87    };88}⋯
36scaledCircle ← Circle[radius=15.0], success ← Success[value=42]⋯135double scaleFactor = 3.0;136Shape scaledCircle→ Circle[radius=15.0] = ShapeProcessor.scale(circleCircle[radius=5.0], scaleFactor3.0);137System.out.println("Original: " + circleCircle[radius=5.0]);138System.out.println("Scaled " + scaleFactor3.0 + "x: " + scaledCircleCircle[radius=15.0]);139140// Result type example141System.out.println("\n--- Result Type ---");142Result<Integer> success→ Success[value=42] = new Success<>(42);143Result<Integer> failure→ Failure[error=Division by zero] = new Failure<>("Division by zero");144145processResult(successSuccess[value=42]);146processResult(failure);⋯outputOriginal: Circle[radius=5.0]
Scaled 3.0x: Circle[radius=15.0]

--- Result Type ---
37static void processResult(Result<Integer> result)pass 1 of 2⋯145    processResult(successSuccess[value=42]);146    processResult(failureFailure[error=Division by zero]);147    148    System.out.println("\n=== Benefits ===");149    System.out.println("""150        Records + Sealed:151        1. Records are implicitly final (perfect for sealed permits)152        2. Record patterns enable deconstruction in switch153        3. Compact syntax for value objects154        4. Automatic equals/hashCode/toString155        5. Guards can add extra conditions156        157        Common patterns:158        - Shape hierarchies159        - Expression trees (AST)160        - Result/Either types161        - Event types162        - Command patterns163        """);164}165166// Process result with pattern matching167static void processResult(Result<Integer> resultSuccess[value=42]) {168    switch (result) {⋯
38static void processResult(Result<Integer> result)pass 2 of 2⋯145    processResult(success);146    processResult(failureFailure[error=Division by zero]);147    148    System.out.println("\n=== Benefits ===");149    System.out.println("""150        Records + Sealed:151        1. Records are implicitly final (perfect for sealed permits)152        2. Record patterns enable deconstruction in switch153        3. Compact syntax for value objects154        4. Automatic equals/hashCode/toString155        5. Guards can add extra conditions156        157        Common patterns:158        - Shape hierarchies159        - Expression trees (AST)160        - Result/Either types161        - Event types162        - Command patterns163        """);164}165166// Process result with pattern matching167static void processResult(Result<Integer> resultFailure[error=Division by zero]) {168    switch (result) {⋯output
=== Benefits ===
Records + Sealed:
1. Records are implicitly final (perfect for sealed permits)
2. Record patterns enable deconstruction in switch
3. Compact syntax for value objects
4. Automatic equals/hashCode/toString
5. Guards can add extra conditions

Common patterns:
- Shape hierarchies
- Expression trees (AST)
- Result/Either types
- Event types
- Command patterns

All 5 passes — pass 1 is the card above
pass	`shape`
1	Circle[radius=5.0]
2	Rectangle[width=4.0, height=6.0]
3	Rectangle[width=5.0, height=5.0]
4	Triangle[a=3.0, b=3.0, c=3.0]
5	Triangle[a=3.0, b=4.0, c=5.0]

All 5 passes — pass 1 is the card above
pass	`shape`
1	Circle[radius=5.0]
2	Rectangle[width=4.0, height=6.0]
3	Rectangle[width=5.0, height=5.0]
4	Triangle[a=3.0, b=3.0, c=3.0]
5	Triangle[a=3.0, b=4.0, c=5.0]

All 4 passes — pass 1 is the card above
pass	`width`	`height`
1	4.0	6.0
2	5.0	5.0
3	4.0	6.0
4	5.0	5.0

All 4 passes — pass 1 is the card above
pass	`b`	`c`	`s`
1	3.0	3.0	4.5
2	4.0	5.0	6.0
3	3.0	3.0	4.5
4	4.0	5.0	6.0

All 5 passes — pass 1 is the card above
pass	`shape`	`total`	`radius`
1	Circle[radius=5.0]	0.0	5.0
2	Rectangle[width=4.0, height=6.0]	78.53981633974483	—
3	Rectangle[width=5.0, height=5.0]	102.53981633974483	—
4	Triangle[a=3.0, b=3.0, c=3.0]	127.53981633974483	—
5	Triangle[a=3.0, b=4.0, c=5.0]	131.4369306567748	—

All 5 passes — pass 1 is the card above
pass	`shape`
1	Circle[radius=5.0]
2	Rectangle[width=4.0, height=6.0]
3	Rectangle[width=5.0, height=5.0]
4	Triangle[a=3.0, b=3.0, c=3.0]
5	Triangle[a=3.0, b=4.0, c=5.0]

All 5 passes — pass 1 is the card above
pass	`shape`
1	Circle[radius=5.0]
2	Rectangle[width=4.0, height=6.0]
3	Rectangle[width=5.0, height=5.0]
4	Triangle[a=3.0, b=3.0, c=3.0]
5	Triangle[a=3.0, b=4.0, c=5.0]

All 4 passes — pass 1 is the card above
pass	`width`	`height`
1	4.0	6.0
2	5.0	5.0
3	4.0	6.0
4	5.0	5.0

All 4 passes — pass 1 is the card above
pass	`b`	`c`	`s`
1	3.0	3.0	4.5
2	4.0	5.0	6.0
3	3.0	3.0	4.5
4	4.0	5.0	6.0

All 5 passes — pass 1 is the card above
pass	`shape`	`total`	`radius`
1	Circle[radius=5.0]	0.0	5.0
2	Rectangle[width=4.0, height=6.0]	78.53981633974483	—
3	Rectangle[width=5.0, height=5.0]	102.53981633974483	—
4	Triangle[a=3.0, b=3.0, c=3.0]	127.53981633974483	—
5	Triangle[a=3.0, b=4.0, c=5.0]	131.4369306567748	—

All 5 passes — pass 1 is the card above
pass	`shape`
1	Circle[radius=5.0]
2	Rectangle[width=4.0, height=6.0]
3	Rectangle[width=5.0, height=5.0]
4	Triangle[a=3.0, b=3.0, c=3.0]
5	Triangle[a=3.0, b=4.0, c=5.0]

All 5 passes — pass 1 is the card above
pass	`shape`
1	Circle[radius=5.0]
2	Rectangle[width=4.0, height=6.0]
3	Rectangle[width=5.0, height=5.0]
4	Triangle[a=3.0, b=3.0, c=3.0]
5	Triangle[a=3.0, b=4.0, c=5.0]

All 4 passes — pass 1 is the card above
pass	`width`	`height`
1	4.0	6.0
2	5.0	5.0
3	4.0	6.0
4	5.0	5.0

All 4 passes — pass 1 is the card above
pass	`b`	`c`	`s`
1	3.0	3.0	4.5
2	4.0	5.0	6.0
3	3.0	3.0	4.5
4	4.0	5.0	6.0

All 5 passes — pass 1 is the card above
pass	`shape`	`total`	`radius`
1	Circle[radius=5.0]	0.0	5.0
2	Rectangle[width=4.0, height=6.0]	78.53981633974483	—
3	Rectangle[width=5.0, height=5.0]	102.53981633974483	—
4	Triangle[a=3.0, b=3.0, c=3.0]	127.53981633974483	—
5	Triangle[a=3.0, b=4.0, c=5.0]	131.4369306567748	—

Records as permitted subclasses give concise data carriers with controlled hierarchy.

Exercise: Practical.java

Model a state machine with sealed classes