[Java] Super keyword

 Super keyword

- The super keyword is a reference variable that is used to refer immediate parent class object

1. Usage

- super is used to refer immediate parent class instance variable

- super() is used to invoke immediate parent class constructor

- super is used to invoke immediate parent class method

2. parent class instance variable

class Vehicle{ int speed = 50; } public class Bike extends Vehicle{ int speed = 100; void display(){ System.out.println(super.speed); } public static void main(String[]args){ Bike a = new Bike(); a.display(); } }

- 50

3. To invoke parent class constructor

class Vehicle{ Vehicle(){ System.out.println("Vehicle"); } } public class Bike extends Vehicle{ Bike(){ super(); System.out.println("Bike"); } public static void main(String[]args){ Bike a = new Bike(); } }  

- vehicle, bike

- super() is added in each class constructor automatically by compiler

- If In the above example Bike doesn't have a super(), It will print out same result

4. To invoke parent class method

- It should be used in case subclass contains the same method as parent class

package stepByStep; class Vehicle{ void message(){ System.out.println("Vehicle"); } } public class Bike extends Vehicle{ void message(){ System.out.println("Bike"); } void display(){ message(); super.message(); } public static void main(String[]args){ Bike a = new Bike(); a.display(); } }  

- In case there is no method in subclass as parent, there is no need to use super.

class Vehicle{ void message(){ System.out.println("Vehicle"); } } public class Bike extends Vehicle{ void display(){ message(); } public static void main(String[]args){ Bike a = new Bike(); a.display(); } }