How to create an Immutable (unchangeable) class in Java?

To create an immutable class in Java, you need to:

• Make the class final so it cannot be subclassed or have its behavior changed.
• Make all fields private and final.
• Do not provide setters.
• Initialize all fields through the constructor.
• If fields are mutable objects, return their copies in getters to prevent modification of internal state.

Example:

public final class ImmutablePerson {
    private final String name;
    private final int age;

    public ImmutablePerson(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

If there are fields of collection types or other objects, you should return their copies or use immutable collections.