Fundamentals of Java

calendarNov 17, 2024 · 3 min read · Java

Super and This keywords of Java

Super Keyword:

Definition: super is a reference to the immediate parent class of the current object. It is mainly used in the context of inheritance.

Usage:

  1. Call the parent class's constructor: super() can be used to call the constructor of the parent class. This is often used to initialize inherited fields. 2.Access parent class methods: If a method in the subclass overrides a method in the parent class, super can be used to call the parent class’s version of the method.
  2. Access parent class fields: super can be used to access fields in the parent class if they are hidden by fields in the subclass.
 1//super keyword is used to access the super class constructor.
 2class Rectangle {
 3    int length;
 4    int breadth;
 5    int x = 10;
 6
 7    Rectangle(int length, int breadth) {
 8        this.length = length;
 9        this.breadth = breadth;
10
11    }
12
13}
14
15class Cuboid extends Rectangle {
16    int height;
17    int x = 20;
18
19    Cuboid(int l, int b, int h) {
20        super(l, b);
21        height = h;
22    }
23
24    void display() {
25        System.out.println(super.x);
26        System.out.println(x);
27        System.out.println(this.x);
28
29    }
30
31    public static void main(String args[]) {
32        Cuboid c1 = new Cuboid(10, 20, 30);
33        c1.display();
34
35    }
36}

This Keyword:

Definition: this is a reference to the current object whose method or constructor is being called.

Usage:

  1. Access instance variables: When a parameter or local variable has the same name as an instance variable, this is used to distinguish between them.
  2. Call another constructor in the same class: this() can be used to invoke another constructor within the same class.
  3. Pass the current object as a parameter: You can pass this as an argument to another method.
 1class Reactangle {
 2    int length;
 3    int breadth;
 4
 5    Reactangle(int length, int breadth) {
 6        this.length = length;// if we will take the name of parameter variables same as our class variables
 7        // then there will be a problem since if we write length=length, it means we're
 8        // assigning the value to itself only and no value is assigned to our class
 9        // variable to avoid this we use this keyword which indicates to the class
10        // variable while comparing it with parameterized variable.(this keyword is used to avoid the name conflict.)
11        this.breadth = breadth;
12
13    }
14
15    void display() {
16        System.out.println("length:" + this.length);
17        System.out.println("breadth:" + this.breadth);
18    }
19
20    public static void main(String[] args) {
21        Reactangle r1 = new Reactangle(2, 5);
22        Reactangle r2 = new Reactangle(3, 4);
23        r1.display();
24        r2.display();
25    }
26}

Key Differences:

  1. this refers to the current object, whereas super refers to the immediate parent class.
  2. this() is used to call a constructor in the same class, while super() calls the constructor of the parent class.
  3. this can only be used in non-static methods or constructors, while super can also be used similarly in instance methods or constructors.