Java final Keyword

final Variable — a Constant

A final variable can be assigned a value exactly once. For a primitive, that means its value can never change afterward; for a reference type, it means the variable can never be reassigned to point at a different object, although the object it points to can still be mutated internally if that object itself is mutable. By convention, final constants are named in UPPER_SNAKE_CASE.

final Method — Cannot Be Overridden

A final method can be inherited and called by subclasses, but it cannot be overridden. This is useful when a superclass needs to guarantee that a piece of logic behaves identically in every subclass, such as a security check or a core algorithm step that must not be altered.

final Class — Cannot Be Extended

A final class cannot be subclassed at all; attempting extends on it is a compile-time error. The standard library uses this for classes whose behavior must never be altered by inheritance — String, Integer, and the other wrapper classes are all declared final.

Example

class Payment {
    static final double TAX_RATE = 0.08; // final variable, a constant

    final double totalWithTax(double amount) { // final method, cannot be overridden
        return amount + (amount * TAX_RATE);
    }
}

final class CreditCardPayment extends Payment {
    // final class — CreditCardPayment itself cannot be extended further
}

public class FinalDemo {
    public static void main(String[] args) {
        CreditCardPayment payment = new CreditCardPayment();
        System.out.println(payment.totalWithTax(100.0));
    }
}

108.0

Exercise

This program does not compile, because it reassigns a final variable. Remove the illegal line, keep the legal one, and notice that changing an element of a final array is allowed.

Expected output: [10, 2, 3]

import java.util.Arrays;

public class FinalDemo {
    public static void main(String[] args) {
        final int[] scores = {1, 2, 3};

        scores[0] = 10;
        scores = new int[] {7, 8, 9};

        System.out.println(Arrays.toString(scores));
    }
}

import java.util.Arrays;

public class FinalDemo {
    public static void main(String[] args) {
        final int[] scores = {1, 2, 3};

        scores[0] = 10;

        System.out.println(Arrays.toString(scores)); // [10, 2, 3]
    }
}

Quick quiz

Interview questions

Go deeper

• final vs finally vs finalize