Difference Between super and this keyword in Java

The following article describes the Difference Between super and this keyword in Java.

For the purpose of referring specific instances, we use super and this keywords in Java in a class hierarchy. As a matter of fact, the super keyword refers to the parent class of the current class. Meanwhile, we can also use it to access members of the parent class that have been overridden by members of the current class. For example, if a subclass defines a method with the same name as a method in its parent class, we can use the super keyword to call the parent class’s implementation of the method. The following code example demonstrates the use of the super keyword to call a parent class’s method.

class Animal {
   public void move() {
      System.out.println("Animals can move");
   }
}

class Dog extends Animal {
   public void move() {
      super.move();
      System.out.println("Dogs can walk and run");
   }
}

In this example, the Dog class extends the Animal class and overrides its move method. When the Dog class’s move method is called, it first calls the move method of the parent class (Animal) using the super keyword, and then adds its own behavior. The output of this code will be:

Animals can move
Dogs can walk and run

On the other hand, we use the this keyword, to refer to the current instance of an object. Also, we can use it to access members of the current class, or to call other constructors in the same class. The following code example demonstrates how to use the this keyword to call another constructor in the same class.

class Rectangle {
   private int length;
   private int width;

   public Rectangle(int length, int width) {
      this.length = length;
      this.width = width;
   }

   public Rectangle(int side) {
      this(side, side);
   }
}

In this example, the Rectangle class has two constructors. The second constructor takes a single argument side, and calls the first constructor using the this keyword, passing the same value for both the length and width arguments. This allows for creating a square rectangle by passing a single value for its side length.

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