What is the super keyword in Java?

The concept of super keyword comes with the idea of inheritance in Java. Suppose you have a member variable or method of the same name in the derived class as you do in the base class.

When referring to that variable/method, how would the program know which one are you referring to; the base class or the derived class?

This is where super comes into play. The super keyword in Java acts like a reference variable to the parent class.

It’s mainly used when we want to access a variable, method, or constructor in the base class, from the derived class.

Let’s have a look at some examples to understand how exactly the super keyword works.

Examples

1. Accessing base class variables

When we have the data members of the same name in both the base and derived class, we can use the super keyword to access the base class member, data, in the derived class.

The snippet below shows how to do this:

// Base Class
class Base { 
    int num = 30; 
} 
  
// Derived Class
class Derived extends Base { 
    int num = 20;
    void callThis() { 
        // print `num` of both classes
        System.out.println("Base `num`: " + super.num);
        System.out.println("Derived `num`: " + num); 
    } 
} 
  
/* Driver Routine */
class Test { 
    public static void main(String[] args) { 
        Derived temp = new Derived(); 
        temp.callThis(); 
    }
}

2. Invoking base class method

When the name of a function if the same in both the base and derived class, the super keyword can be used to invoke the base class function in the derived class.

The snippet below shows how to do this:

// Base Class
class Base { 
    void display(){
      System.out.println("Base Class");
    }
} 
  
// Derived Class
class Derived extends Base {
    // invoke `display()` method for both the classes
    void callThis(){
      super.display();
      display();
    }
    void display(){
      System.out.println("Derived Class");
    }
} 
  
/* Driver Routine */
class Test { 
    public static void main(String[] args) { 
        Derived temp = new Derived(); 
        temp.callThis(); 
    }
}

3. Invoking base class constructor

The super keyword can also be used to invoke the parent class constructor, both parameterized and empty, in the derived class.

// Base Class
class Base { 
    Base(){
      System.out.println("Base Class Constructor");
    }
} 
  
// Derived Class
class Derived extends Base {
    // invoke `display()` method for both the classes
    Derived(){
        super();
        System.out.println("Derived Class Constructor");
    }
} 
  
/* Driver Routine */
class Test { 
    public static void main(String[] args) { 
        Derived temp = new Derived(); 
    }
}

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