How to implement a class whose instances cannot be modified after creation in Java?

To make a class in Java immutable, you should:

• Declare the class as final so it cannot be subclassed and its behavior cannot be changed.
• Make all fields private and final.
• Do not provide setters for the fields.
• Initialize all fields through the constructor.
• If the fields are mutable objects (e.g., arrays or collections), create copies of them when passing to the constructor and when returning from getters.

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;
    }
}