The super keyword in Java is a reference variable that is used to refer to the immediate parent class object.
Whenever you create the instance of a subclass, an instance of parent class is created implicitly which is referred by super reference variable.
Usage of Java super Keyword
- super can be used to refer to the immediate parent class instance variable.
- super can be used to invoke the immediate parent class method.
- super() can be used to invoke immediate parent class constructor.
1) super is used to refer to immediate parent class instance variable
We can use super keyword to access the data member or field of the parent class. It is used if parent class and child class have the same fields.
class Animal{
String color="white";
}
class Dog extends Animal{
String color="black";
void printColor(){
System.out.println(color);//prints color of Dog class
System.out.println(super.color);//prints color of Animal class
}
}
class TestSuper1{
public static void main(String args[]){
Dog d=new Dog();
d.printColor();
}}In the above example, Animal and Dog both classes have a common property color. If we print the color property, it will print the color of the current class by default. To access the parent property, we need to use super keyword.
2) super can be used to invoke the immediate parent class method
The super keyword can also be used to invoke the parent class method. It should be used if the subclass contains the same method as the parent class. In other words, it is used if the method is overridden.
class Animal{
void eat(){System.out.println("eating...");}
}
class Dog extends Animal{
void eat(){System.out.println("eating bread...");}
void bark(){System.out.println("barking...");}
void work(){
super.eat();
bark();
}
}
class TestSuper2{
public static void main(String args[]){
Dog d=new Dog();
d.work();
}}In the above example Animal and Dog both classes have eat() method if we call eat() method from Dog class, it will call the eat() method of Dog class by default because priority is given to local.
To call the parent class method, we need to use the super keyword.
3) super() can be used to invoke immediate parent class constructor
The super keyword can also be used to invoke the parent class constructor. Let's see a simple example:
class Animal{
Animal(){System.out.println("animal is created");}
}
class Dog extends Animal{
Dog(){
super();
System.out.println("dog is created");
}
}
class TestSuper3{
public static void main(String args[]){
Dog d=new Dog();
}}