Overriding in Java

In any object-oriented programming language, Overriding is a feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its super-classes or parent classes. 

If subclass (child class) has the same method as declared in the parent class, it is known as method overriding in Java.

Method overriding is used for runtime polymorphism. The version of a method that is executed will be determined by the object that is used to invoke it. If an object of a parent class is used to invoke the method, then the version in the parent class will be executed, but if an object of the subclass is used to invoke the method, then the version in the child class will be executed.

Rules for Java Method Overriding

1. The method must have the same name as in the parent class
2. The method must have the same parameter as in the parent class.
3. There must be an IS-A relationship (inheritance).

Example:

// Base Class

class Parent {

            void show()

            {

                        System.out.println("Parent's show()");

            }

}

// Inherited class

class Child extends Parent {

            void show()  //override method

           {

                        System.out.println("Child's show()");

            }

}

class Main {

            public static void main(String[] args)

            {

                        Parent obj1 = new Parent();

                        obj1.show();

Parent obj2 = new Child();

                        obj2.show();

            }

}

Points to note:

1. Overriding and Access-Modifiers: The access modifier for an overriding method can allow more, but not less, access than the overridden method.

For example, a protected instance method in the super-class can be made public, but not private, in the subclass.

2. Final methods cannot be overridden

3. Static methods cannot be overridden (When a static method is defined with same signature as a static method in base class, it is known as method hiding).

Difference between method overloading and method overriding

	Method Overloading	Method Overriding
1)	Method overloading is used to increase the readability of the program.	Method overriding is used to provide the specific implementation of the method that is already provided by its super class.
2)	Method overloading is performed within class.	Method overriding occurs in two classes that have IS-A (inheritance) relationship.
3)	In case of method overloading, parameter must be different.	In case of method overriding, parameter must be same.
4)	Method overloading is the example of compile time polymorphism.	Method overriding is the example of run time polymorphism.