Data Types

Strings

Working with Text

You're building a greeting card generator. The user enters their name "Alice" and you need to create "Hello, Alice!" - combining text, storing it, measuring it, and accessing individual letters.

Store and print a name

Create a string and display it.

Name.java 
public class Name {
    public static void main(String[] args) {
        String name = ;
        System.out.println("Hello, " + name + "!");
        System.out.println("Your name is: " + name);
    }
}

public class Name {
    public static void main(String[] args) {
        String name = ;
        System.out.println("Hello, " + name + "!");
        System.out.println("Your name is: " + name);
    }
}

public class Name {
    public static void main(String[] args) {
        String name = ;
        System.out.println("Hello, " + name + "!");
        System.out.println("Your name is: " + name);
    }
}

Strings use double quotes in Java. Single quotes are for single characters.

String A sequence of characters, like `"Hello"`. Immutable in Java.

Combine first and last name

Concatenate strings using the + operator.

Combine.java 
public class Combine {
    public static void main(String[] args) {
        String firstName = ;
        String lastName = ;
        
        String fullName = firstName + " " + lastName;
        System.out.println("Full name: " + fullName);
        
        // Building a greeting
        String greeting = "Hello, " + fullName + "!";
        System.out.println(greeting);
    }
}

public class Combine {
    public static void main(String[] args) {
        String firstName = ;
        String lastName = ;
        
        String fullName = firstName + " " + lastName;
        System.out.println("Full name: " + fullName);
        
        // Building a greeting
        String greeting = "Hello, " + fullName + "!";
        System.out.println(greeting);
    }
}

public class Combine {
    public static void main(String[] args) {
        String firstName = ;
        String lastName = ;
        
        String fullName = firstName + " " + lastName;
        System.out.println("Full name: " + fullName);
        
        // Building a greeting
        String greeting = "Hello, " + fullName + "!";
        System.out.println(greeting);
    }
}

public class Combine {
    public static void main(String[] args) {
        String firstName = ;
        String lastName = ;
        
        String fullName = firstName + " " + lastName;
        System.out.println("Full name: " + fullName);
        
        // Building a greeting
        String greeting = "Hello, " + fullName + "!";
        System.out.println(greeting);
    }
}

public class Combine {
    public static void main(String[] args) {
        String firstName = ;
        String lastName = ;
        
        String fullName = firstName + " " + lastName;
        System.out.println("Full name: " + fullName);
        
        // Building a greeting
        String greeting = "Hello, " + fullName + "!";
        System.out.println(greeting);
    }
}

public class Combine {
    public static void main(String[] args) {
        String firstName = ;
        String lastName = ;
        
        String fullName = firstName + " " + lastName;
        System.out.println("Full name: " + fullName);
        
        // Building a greeting
        String greeting = "Hello, " + fullName + "!";
        System.out.println(greeting);
    }
}

public class Combine {
    public static void main(String[] args) {
        String firstName = ;
        String lastName = ;
        
        String fullName = firstName + " " + lastName;
        System.out.println("Full name: " + fullName);
        
        // Building a greeting
        String greeting = "Hello, " + fullName + "!";
        System.out.println(greeting);
    }
}

public class Combine {
    public static void main(String[] args) {
        String firstName = ;
        String lastName = ;
        
        String fullName = firstName + " " + lastName;
        System.out.println("Full name: " + fullName);
        
        // Building a greeting
        String greeting = "Hello, " + fullName + "!";
        System.out.println(greeting);
    }
}

public class Combine {
    public static void main(String[] args) {
        String firstName = ;
        String lastName = ;
        
        String fullName = firstName + " " + lastName;
        System.out.println("Full name: " + fullName);
        
        // Building a greeting
        String greeting = "Hello, " + fullName + "!";
        System.out.println(greeting);
    }
}
concatenation Joining strings with `+`: `"Hello" + " " + "World"` → `"Hello World"`

Get string length

Find out how many characters are in a string.

Length.java 
public class Length {
    public static void main(String[] args) {
        String word = ;
        String sentence = "Hello World";
        
        System.out.println("'" + word + "' has " + word.length() + " characters");
        System.out.println("'" + sentence + "' has " + sentence.length() + " characters");
        
        // Empty string has length 0
        String empty = "";
        System.out.println("Empty string length: " + empty.length());
    }
}

public class Length {
    public static void main(String[] args) {
        String word = ;
        String sentence = "Hello World";
        
        System.out.println("'" + word + "' has " + word.length() + " characters");
        System.out.println("'" + sentence + "' has " + sentence.length() + " characters");
        
        // Empty string has length 0
        String empty = "";
        System.out.println("Empty string length: " + empty.length());
    }
}

public class Length {
    public static void main(String[] args) {
        String word = ;
        String sentence = "Hello World";
        
        System.out.println("'" + word + "' has " + word.length() + " characters");
        System.out.println("'" + sentence + "' has " + sentence.length() + " characters");
        
        // Empty string has length 0
        String empty = "";
        System.out.println("Empty string length: " + empty.length());
    }
}
length Number of characters: `"Hello".length()` → `5`

Compare two strings

Check if strings are equal - but be careful with == in Java!

Compare.java 
public class Compare {
    public static void main(String[] args) {
        String a = "hello";
        String b = "hello";
        String c = "Hello";  // different case
        
        // Use .equals() for content comparison
        System.out.println("a.equals(b): " + a.equals(b));       // true
        System.out.println("a.equals(c): " + a.equals(c));       // false (case matters)
        System.out.println("a.equalsIgnoreCase(c): " + a.equalsIgnoreCase(c));  // true
        
        // Comparing with user input
        String input = ;
        if (input.equalsIgnoreCase("yes")) {
            System.out.println("User agreed!");
        }
        
    }
}

public class Compare {
    public static void main(String[] args) {
        String a = "hello";
        String b = "hello";
        String c = "Hello";  // different case
        
        // Use .equals() for content comparison
        System.out.println("a.equals(b): " + a.equals(b));       // true
        System.out.println("a.equals(c): " + a.equals(c));       // false (case matters)
        System.out.println("a.equalsIgnoreCase(c): " + a.equalsIgnoreCase(c));  // true
        
        // Comparing with user input
        String input = ;
        if (input.equalsIgnoreCase("yes")) {
            System.out.println("User agreed!");
        }
        
    }
}

public class Compare {
    public static void main(String[] args) {
        String a = "hello";
        String b = "hello";
        String c = "Hello";  // different case
        
        // Use .equals() for content comparison
        System.out.println("a.equals(b): " + a.equals(b));       // true
        System.out.println("a.equals(c): " + a.equals(c));       // false (case matters)
        System.out.println("a.equalsIgnoreCase(c): " + a.equalsIgnoreCase(c));  // true
        
        // Comparing with user input
        String input = ;
        if (input.equalsIgnoreCase("yes")) {
            System.out.println("User agreed!");
        }
        
    }
}

Always use .equals() for string comparison, not ==.

Access character by index

Get individual characters from a string by their position.

Index.java 
public class Index {
    public static void main(String[] args) {
        String word = ;
        
        // Index:    0 1 2 3 4
        // Chars:    H e l l o
        
        char first = word.charAt(0);
        char last = word.charAt(word.length() - 1);
        
        System.out.println("Word: " + word);
        System.out.println("First character: " + first);
        System.out.println("Last character: " + last);
        
        // Print all characters with their indices
        for (int i = 0; i < word.length(); i++) {
            System.out.println("Index " + i + ": " + word.charAt(i));
        }
    }
}

public class Index {
    public static void main(String[] args) {
        String word = ;
        
        // Index:    0 1 2 3 4
        // Chars:    H e l l o
        
        char first = word.charAt(0);
        char last = word.charAt(word.length() - 1);
        
        System.out.println("Word: " + word);
        System.out.println("First character: " + first);
        System.out.println("Last character: " + last);
        
        // Print all characters with their indices
        for (int i = 0; i < word.length(); i++) {
            System.out.println("Index " + i + ": " + word.charAt(i));
        }
    }
}

public class Index {
    public static void main(String[] args) {
        String word = ;
        
        // Index:    0 1 2 3 4
        // Chars:    H e l l o
        
        char first = word.charAt(0);
        char last = word.charAt(word.length() - 1);
        
        System.out.println("Word: " + word);
        System.out.println("First character: " + first);
        System.out.println("Last character: " + last);
        
        // Print all characters with their indices
        for (int i = 0; i < word.length(); i++) {
            System.out.println("Index " + i + ": " + word.charAt(i));
        }
    }
}

Positions start at 0. First character is at index 0, second at index 1, etc.

charAt Get character at position: `"Hello".charAt(0)` → `'H'`

Exercise: Special.java

Explore special strings: empty string, escape sequences, multiline