super Keyword in Java

"super" Keyword in Java

Introduction

super keyword is a reference variable in Java.
It is used to refer to the immediate parent class object (i.e., the superclass of the current object).
This keyword is mainly used in inheritance when a subclass needs to access members (methods, constructors, or variables) of its parent class.
Use of super Keyword:
1. It is used to refer the parent class instance variable.
2. It is used to refer to the parent class method.
3. It is used to refer to the parent class constructor.

1. It is used to refer the parent class instance variable.

Java Program Example 1:

class Parent
{
    int num = 100;
}

class Child extends Parent
{
    int num = 200;

    void display()
    {
        System.out.println("Child num: " + num);
        System.out.println("Parent num: " + super.num);  // referring to parent class variable
    }
}

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

Output:

Child num: 200
Parent num: 100

2. It is used to refer to the parent class method.

Java Program Example:

public class ThisDemo
{
    void showMessage()
    {
        System.out.println("Hello from showMessage() method");
    }

    void display()
    {
        // Calling another method of the same class using 'this'
        this.showMessage();  // Optional: can also call showMessage() directly
        System.out.println("Inside display() method");
    }

    public static void main(String[] args)
    {
        ThisDemo obj = new ThisDemo();
        obj.display();
    }
}

Output:

Hello from showMessage() method
Inside display() method

3. It is used to refer to the parent class constructor.

Java Program Example:

package notesprogram;

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

class Child extends Parent
{
    Child()
    {
        super(); // calls Parent's constructor
        System.out.println("Child constructor called");
    }
}

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

Output:

Parent constructor called
Child constructor called

Note : super() must be the first statement in a constructor
- If used, the call to the parent class constructor (super()) must appear as the very first statement in the child class constructor.

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"super" Keyword in Java

Introduction

1. It is used to refer the parent class instance variable.

Output:

2. It is used to refer to the parent class method.

Output:

3. It is used to refer to the parent class constructor.

Output:

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