• Vairable, then its value cannot be changed once initialized.
• Method, then it cannot be overridden by subclasses.
• Class, then it cannot be subclassed or extended.

public class FinalDemo
{
    public static void main(String[] args)
    {
        final int MAX_MARKS = 100;  // final variable (constant)
        System.out.println("Maximum marks allowed: " + MAX_MARKS);

        //MAX_MARKS = MAX_MARKS + 50;     //error as we cannot change the final variable value
    }
}

Maximum marks allowed: 100

class Parent
{
    final void showMessage()
    {
        System.out.println("This is a final method from the Parent class.");
    }
}

class Child extends Parent
{
    // Trying to override the final method will cause a compile-time error
    /*
    void showMessage()
    {
        System.out.println("Trying to override.");
    }
    */
}

public class FinalDemo
{
    public static void main(String[] args)
    {
        Child obj = new Child();
        obj.showMessage();
    }
}

This is a final method from the Parent class.

// Final class - cannot be extended
final class A
{
    void mA()
    {
        System.out.println("This is class A.");
    }
}

// Trying to extend a final class will cause a compile-time error
/*
class B extends A
{

}
*/

public class FinalDemo
{
    public static void main(String[] args)
    {
        A obj = new A();
        obj.mA();
    }
}

This is class A.