this vs super Keyword in Java

When working with Java classes, two important keywords, this and super, help in handling instance variables and inheritance. In this blog, we will understand these keywords with explanations and examples.

What is this Keyword?#

The this keyword refers to the current instance of a class. It is mainly used to differentiate between instance variables and parameters with the same name, invoke constructors within the same class, and pass the current instance to a method.

Uses of this Keyword#

• Referring to instance variables
• Calling another constructor in the same class
• Passing the current object as a parameter
• Returning the current instance from a method

Example: Using this to refer to instance variables#

class Student {
    String name;
    int age;

    // Constructor
    Student(String name, int age) {
        this.name = name; // 'this' differentiates instance variable and parameter
        this.age = age;
    }

    void display() {
        System.out.println("Name: " + this.name + ", Age: " + this.age);
    }
}

public class Main {
    public static void main(String[] args) {
        Student s1 = new Student("John", 22);
        s1.display();
    }
}

Output:#

Name: John, Age: 22

Example: Using this to call another constructor#

class Person {
    String name;
    int age;

    // Default constructor
    Person() {
        this("Unknown", 0); // Calls parameterized constructor
    }

    // Parameterized constructor
    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    void display() {
        System.out.println("Name: " + name + ", Age: " + age);
    }
}

public class Main {
    public static void main(String[] args) {
        Person p1 = new Person();
        p1.display();
    }
}

Output:#

Name: Unknown, Age: 0

What is super Keyword?#

The super keyword is used in inheritance to refer to the parent class. It is mainly used to access parent class members, invoke parent class methods, and call parent class constructors.

Uses of super Keyword#

• Accessing parent class methods
• Calling the parent class constructor
• Accessing parent class variables

Example: Using super to call parent class methods#

class Animal {
    void makeSound() {
        System.out.println("Animals make sound");
    }
}

class Dog extends Animal {
    void makeSound() {
        super.makeSound(); // Calls the makeSound() of Animal class
        System.out.println("Dogs bark");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog d = new Dog();
        d.makeSound();
    }
}

Output:#

Animals make sound
Dogs bark

Example: Using super to call parent class constructor#

class Parent {
    Parent() {
        System.out.println("Parent class constructor");
    }
}

class Child extends Parent {
    Child() {
        super(); // Calls the parent class constructor
        System.out.println("Child class constructor");
    }
}

public class Main {
    public static void main(String[] args) {
        Child c = new Child();
    }
}

Output:#

Parent class constructor
Child class constructor

Difference Between this and super#

Conclusion#

In this blog, we learned about the this and super keywords in Java. The this keyword is used for referring to the current instance, differentiating instance variables, and calling constructors within the same class. The super keyword is used to refer to the parent class, access its members, and call its constructor. Understanding these concepts is crucial for working with object-oriented programming and inheritance in Java.