Withers (copy with a change)

Definition

A "wither" is a method that returns a copy of an immutable object with one value changed, for example withEmail(...). It gives you the convenience of updating without making the object mutable.

Example code

Changing one field by creating a modified copy

record User(String name, String email, int age) {
    User withEmail(String newEmail) { return new User(name, newEmail, age); }
    User withAge(int newAge) { return new User(name, email, newAge); }
}

class Demo {
    public static void main(String[] args) {
        User original = new User("Asha", "asha@old.com", 30);
        User updated = original.withEmail("asha@new.com").withAge(31);

        System.out.println(original);      // unchanged
        System.out.println(updated);       // the modified copy
    }
}

// Output:
// User[name=Asha, email=asha@old.com, age=30]
// User[name=Asha, email=asha@new.com, age=31]