super keyword

super Keyword

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

Usage of super Keyword

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.

Problem without super keyword:-

class Student{  

  int marks=50;  

}  

  

class CseStudent extends Student{  

  int marks=100;  

      

  void display(){  

   System.out.println(marks);//will print marks of cse students   

  }  

  public static void main(String args[]){  

   CseStudent cse = new CseStudent();  

   cse.display();  

     

}  

}  

output: 100

super keyword is used to refer the parent class instance variable

class Vehicle{  

  int speed=40;  

}  

  

class Bike extends Vehicle{  

  int speed=100;  

      

  void display(){  

   System.out.println(super.speed);//will print speed of Vehicle now  

  }  

  public static void main(String args[]){  

   Bike b=new Bike();  

   b.display();  

     

}  

}  

output: 40

super keyword is used to invoke parent class constructor

super() must be the first line of constructor and if programmer don't call the constructor,compiler wil automaticlly(imlicitly) call the constructor.

Example

class Vehicle{
          Vehicle()
 {
    System.out.println("Vehicle is created");
 }
}
 
class Bike5 extends Vehicle{
          Bike(){
          super();//will invoke parent class constructor
          System.out.println("Bike is created");
}
  public static void main(String args[]){
   Bike b=new Bike();
      }
}  

output: Vehicle is created
            Bike is created

super keyword is used to invoke the parent class method

Example:

class Person{  
            void message()
{
   System.out.println("welcome");
}  
}  
  
class Student extends Person{  
            void message()
{
  System.out.println("welcome to java");
}  
  
            void display()
{  
               message();//will invoke current class message() method  
               super.message();//will invoke parent class message() method  
}  
  
        public static void main(String args[]){  
        Student s=new Student();  
        s.display();  
    }  

}  

output: welcome to java
            welcome

In the above example Student and Person both classes have message() method if we call message() method from Student class, it will call the message() method of Student class not of Person class because priority is given to local.
In case there is no method in subclass as parent, there is no need to use super.