Method overriding in java

Declaring a method in sub class which is already present in parent class is known as method overriding. Overriding is done so that a child class can give its own implementation to a method which is already provided by the parent class. In this case the method in parent class is called overridden method and the method in child class is called overriding method. In this guide, we will see what is method overriding in Java and why we use it.

Method Overriding Example

Lets take a simple example to understand this. We have two classes: A child class Boy and a parent class Human. The Boy class extends Human class. Both the classes have a common method void eat(). Boy class is giving its own implementation to the eat() method or in other words it is overriding the eat() method.

The purpose of Method Overriding is clear here. Child class wants to give its own implementation so that when it calls this method, it prints Boy is eating instead of Human is eating.

class Human{
   //Overridden method
   public void eat()
   {
      System.out.println("Human is eating");
   }
}
class Boy extends Human{
   //Overriding method
   public void eat(){
      System.out.println("Boy is eating");
   }
   public static void main( String args[]) {
      Boy obj = new Boy();
      //This will call the child class version of eat()
      obj.eat();
   }
}

Let's see the program of method overriding.

 
 package com.ritesh;
 class A{
    public int T1(){
        return  20;
    }
    public  void T2(){
        System.out.println("I am a second  method of class A");
    }
    public  int sum(int a,int b){
        System.out.print("I am a method of class A ");
        return a+b;
    }

    static class B extends A{
        @Override            //check point to check that the method is override or not
        public  int sum(int a,int b){
            System.out.print("I am a method of class b ");
            return a+b;
        }
        @Override         //check point to check that the method is override or not
        public  void T2(){
            System.out.print("I am a first method of class B");
        }
    }
 }

 public class MethodOverriding {
    public static void main(String[] args) {
        A a=new A();
        System.out.println( a.sum(2,4));

        A.B b=new A.B();
        System.out.println(b.sum(10,30));
        System.out.println();
        System.out.println();

        a.T2();
        b.T2();


    }
 }

Rules for Method Overriding

• The argument list should be exactly the same as that of the overridden method.
• The return type should be the same or a subtype of the return type declared in the original overridden method in the superclass.
• The access level cannot be more restrictive than the overridden method's access level. For example: If the superclass method is declared public then the overridding method in the sub class cannot be either private or protected.
• Instance methods can be overridden only if they are inherited by the subclass.
• A method declared final cannot be overridden.
• A method declared static cannot be overridden but can be re-declared.
• If a method cannot be inherited, then it cannot be overridden.
• A subclass within the same package as the instance's superclass can override any superclass method that is not declared private or final.
• A subclass in a different package can only override the non-final methods declared public or protected.
• An overriding method can throw any uncheck exceptions, regardless of whether the overridden method throws exceptions or not. However, the overriding method should not throw checked exceptions that are new or broader than the ones declared by the overridden method. The overriding method can throw narrower or fewer exceptions than the overridden method.
• Constructors cannot be overridden.