'super' Keyword

Lets discuss about one of the interesting and widely used keyword 'super'.super keyword is used to access the properties of the parent class.

super with respect to variables:

We use super keyword when we want to access the variables of the immediate parent class.

Example:

class Parent
{
 int a=5;
}
class Child extends Parent
{
 int a=10;
 void printvalue()
 {
  System.out.println("Child class variable is "+a);  //Child class member
  System.out.println("Parent class variable is "+super.a);  //Parent class member
 }
}
class Mainclass 
{
 public static void main(String []args)
 { 
  Child c=new Child();
  c.printvalue();
 }
}

Output:

Child class variable is 10
Parent class variable is 5

Here if we do not use super the value of a is '10'(child class) if we use super the value initialized in the parent class is assigned to a.

Super with respect to methods:

Super keyword is used to invoke the methods in the immediate parent class.It is especially used incase of method overriding.

class Parent
{
 int i=10;
 void message()
 {
  System.out.println("parent class variable "+i);
 }
}
class Child extends Parent
{
 int i=5;
 void message()
 {
  super.message();
  System.out.println("child class variable"+i);
 }
}
class Mainclass
{
 public static void main(String []args)
 {
  Child c=new Child();
  c.message();
 }
}

Output:

parent class variable is 10.
child class variable is 5.

Super with respect to constructors:

As we all know,constructors are primarily known for initializing the variables.To invoke a parent class constructor,the super must be placed in the first line of the Child class constructor.

class Parent
{
 int i;
 Parent(int b)
 {
  i=b;
 }
}
class Child extends Parent
{
 int i;
 Child(int a,int b)
 {
  super(b);
  i=a;
 }
 void show()
 { 
  System.out.println("child class variable "+i);
  System.out.println("parent class variable"+super.i);
 }
}
class Mainclass
{
 public static void main(String []args)
 {
  Child c=new Child(5,10);
  c.show();
 }
}

Output:

child class variable 5
parent class variable 10 

Note:

In the case of constructors,if the child class does not explicity invoke a parent class constructor,the compiler automatically inserts a call to the no argument constructor of the parent class.If the parent class does not have a no-argument constructor,you will end up with a compilation error.