Mastering super Keyword in Java: A Beginner's Guide to Inheritance

Understanding the super Keyword in Java

When working with inheritance in Java, super keyword plays key role in accessing members (variables, methods, and constructors) of parent class. It helps avoid confusion when subclass and superclass share similar names for methods or variables.

What is super in Java?

In Java, super is reference variable used to refer to immediate parent class object. Whenever you create an instance of subclass, an instance of its superclass is also created, and super points to it.

Common Uses of super in Java

Java allows you to use the super keyword in three main ways:

1. Accessing Parent Class Variables

If subclass has a variable with the same name as the parent class, use super to refer to the parent’s variable.

class Parent {
    int x = 10;
}

class Child extends Parent {
    int x = 20;

    void display() {
        System.out.println("Child x: " + x);
        System.out.println("Parent x: " + super.x);
    }
}

2. Calling Parent Class Methods

If method is overridden in the subclass, you can still access the parent class version using super.

class Parent {
    void show() {
        System.out.println("This is Parent");
    }
}

class Child extends Parent {
    void show() {
        System.out.println("This is Child");
        super.show(); // Call parent method
    }
}

3. Invoking Parent Class Constructor

Use super() to call the constructor of the parent class. It must be the first statement in the child class constructor.

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

class Child extends Parent {
    Child() {
        super(); // Must be first
        System.out.println("Child Constructor");
    }
}