Final classes and methods

The final keyword can be applied to classes and methods to restrict inheritance and overriding.

final classes

A final class cannot be extended (subclassed).

final class ImmutableClass {
    // ...
}
// class Child extends ImmutableClass { } // error

Use cases: Immutability (e.g., String, Integer), security, or design where inheritance would break invariants.

final methods

A final method cannot be overridden by subclasses.

class Parent {
    final void cannotOverride() {
        System.out.println("This method is final");
    }
}

class Child extends Parent {
    // void cannotOverride() { } // error
}

Use cases: Preventing modification of critical behavior, performance (early binding), or ensuring correctness of algorithms.

Comparison

Modifier	Can be extended?	Can be overridden?
final class	No	N/A
non‑final class	Yes	–
final method	–	No
non‑final method	–	Yes

Note: final does not affect static methods (they are hidden, not overridden). Also, final methods can be overloaded (different parameters) – that’s allowed.