Super Keyword in Java

Usage of super Keyword

• Use of super keyword with variables
• Use of super keyword with methods
• Use of super keyword with constructors

1. Use of super keyword with variables

To access the data member or field of the parent class, we can utilize the "super" keyword. This keyword work when both the parent and child classes have fields with the same name.

Java program uses of super keyword with variables

class Vehicle{  
	int maxSpeed = 90;
}  
class Bike extends Vehicle{  
    int maxSpeed = 140; 
    void display(){
    	System.out.println("Bike Class - Maximum Speed: "+ maxSpeed);
        System.out.println("Vehicle Class - Maximum Speed: "+ super.maxSpeed); //print Vehicle class maxSpeed variable 
    }
}   
class alpha{  
	public static void main(String args[]){  
	Bike bike=new Bike();  
	bike.display();
	}
} 

Bike Class - Maximum Speed: 140 

Vehicle Class - Maximum Speed: 90 

2. Use of super keyword with methods

This is used to invoke the parent class method. So, whenever a parent and child class have methods with the same name, we use the super keyword to resolve ambiguity.

class Vehicle{  
	int maxSpeed = 90;
    void SpeedDisplay(){
    	System.out.println("Vehicle Class - Maximum Speed: "+ maxSpeed);
    }
}  
class Bike extends Vehicle{  
    int maxSpeed = 140;
    void SpeedDisplay(){
    	System.out.println("Bike Class - Maximum Speed: "+ maxSpeed);
    }
    void display(){
    	SpeedDisplay();
    	super.SpeedDisplay(); // Vehicle class method get print
    }
}   
class alpha{  
	public static void main(String args[]){  
	Bike bike=new Bike();  
	bike.display();
	}
}

Bike Class - Maximum Speed: 140 

Vehicle Class - Maximum Speed: 90  

3. Use of super keyword with constructors

The "super" keyword has the ability to access the constructor of the parent class. Another important distinction is that, depending on the situation,'super' can invoke both parametric and non-parametric constructors.

class Vehicle{  
	int maxSpeed = 90;
	Vehicle(){
         System.out.println("Vehicle Class - Maximum Speed: "+ maxSpeed);
    }
}  
class Bike extends Vehicle{  
    int maxSpeed = 140;
    Bike(){
      super();
      System.out.println("Bike Class - Maximum Speed: "+ maxSpeed);
    }
}   
class alpha{  
	public static void main(String args[]){  
	  Bike bike=new Bike();  
	}
} 

Bike Class - Maximum Speed: 140 

Vehicle Class - Maximum Speed: 90  

Usage of super Keyword

• Since the superclass has no knowledge of any subclass, any initialization it has to undertake is distinct from and possibly prerequisite to any initialization carried out by the subclass, hence the call to super() must be the first sentence in the Derived(Student) Class constructor. It must therefore finish its execution first.
• In Java, when you create a subclass and if you don't explicitly call any of the superclass's constructors, the compiler automatically adds a call to the no-argument constructor of its superclass.This implies that the compiler will call the superclass's constructor on your behalf if you don't write any code for it.The superclass must have a no-argument constructor in order for this automatic insertion to occur. A compile-time error will appear if the superclass only has constructors with parameters and lacks a no-argument constructor.In these case , you must use the super keyword to explicitly call one of the constructors of the superclass from the subclass.

• If a subclass constructor explicitly or implicitly invokes a constructor of its superclass, you might think that a whole chain of constructors is called, all the way back to the constructor of Object. This is, in fact, the case. It is known as constructor chaining.