super keyword in java

The super keyword in java is a reference variable which is used to refer immediate parent class object.
Whenever you create the instance of subclass, an instance of parent class is created implicitly which is referred by super reference variable.

Usage of super Keyword

  • super can be used to refer immediate parent class instance variable.
  • super can be used to invoke immediate parent class method.
  • super() can be used to invoke immediate parent class constructor.

    • super can be used to refer immediate parent class instance variable.

    We can use super keyword to access the data member or field of parent class. It is used if parent class and child class have same fields.

    Example

    File: TestSuper.java 
    class Person {  
String name = "sanjay";  
  }  
class Child extends Person {  
String name = "rajkumar";  
void printname() {  
System.out.println(name); //prints name of Child class  
System.out.println(super.name); //prints name of Person class  
  } }  
class TestSuper{  
public static void main(String args[]) {  
Child c = new Child();  
c.printname();  
  } }

    Output:

    rajkumar
sanjay
    In the above example, Person and Child both classes have a common property name. If we print name property, it will print the name of current class by default. To access the parent property, we need to use super keyword.

    super can be used to invoke parent class method

    The super keyword can also be used to invoke parent class method. It should be used if subclass contains the same method as parent class. In other words, it is used if method is overridden.

    Example:

    File: TestSuper1.java 
    class Person {  
void eat() {
System.out.println("eating moment");
  } }  
class Child  extends Person {  
void eat() {
System.out.println("eating with milk"); }  
void laugh() { 
System.out.println("laughing moment);  }  
void work() {  
super.eat();  
laugh();  
  } }  
class TestSuper1 {  
public static void main(String args[]) {  
Child c = new Child();  
c.work();  
  } }

    Output:

    eating moment
laughing moment
    In the above example Person and Child both classes have eat() method if we call eat() method from Child class, it will call the eat() method of Child class by default because priority is given to local.
    To call the parent class method, we need to use super keyword.

    super is used to invoke parent class constructor.

    The super keyword can also be used to invoke the parent class constructor.

    Example:

    File: TestSuper2.java 
    class Person {  
Person() {
System.out.println("person can run");
  } }  
class Child extends Person {  
Child() {  
super();  
System.out.println("child can walks");  
  }  }  
class TestSuper2 {  
public static void main(String args[]){  
Child c = new Child();  
  }}

    Output:

    person can run
child can walks

    super example: real use

    see the real use of super keyword. Here, Emp class inherits Person class so all the properties of Person will be inherited to Emp by default. To initialize all the property, we are using parent class constructor from child class. In such way, we are reusing the parent class constructor.

    Example:

    File: TestSuper3.java 
    class Person {  
int id;  
String name;  
Person(int id,String name) {  
this.id=id;  
this.name=name;  
  } }  
class Servant extends Person{  
float salary;  
Servant(int id,String name,float salary) {  
super(id,name);   //reusing parent constructor  
this.salary = salary;  
   }  
void display() { 
System.out.println(id+" "+name+" "+salary);
   } }  
class TestSuper3{  
public static void main(String[] args) {  
Servant s = new Servant(109,"rajkumar",80000f);  
s.display();  
  } }

    Output:

    109 rajkumar 80000