Programming

  minte9
LearnRemember



OOP / Final Keyword

Final

Final classes / methods cannot be extended / overriden. 
 
/**
 * A final class cannot be exended.
 * A final method cannot be overriden.
 */

package com.minte9.oop.final_keyword;

public class Final {
    public static void main(String[] args) {
        new B();
    }
}
class A {    
    public final void getName() { // Look Here

    }
}

final class B extends A {
/*
    public void getName() {
        // Error: override final method
    } 
*/
}

/*
class C extends B { 
    // C cannot subtype finalclass B
}
*/

Constants

Fields that are static and final are constants (it can never change). 
 
/**
 * A static final variables is a constant.
 * It cannot be changed.
 */

package com.minte9.oop.final_keyword;

public class Constants {
    public static void main(String[] args) {
        new MyClass(); // 25
    }
}

class MyClass {
    public static final int FOO = 25; // Look Here

    public MyClass() {
        System.out.println(FOO);

        // FOO++; // Compile Error - Look Here
    }
}




References