Method Overriding In Java

Method Overriding in object oriented programming is a language feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its superclasses or parent classes. The implementation in the subclass overrides (replaces) the implementation in the superclass by providing a method that has same name, same parameters or signature, and same return type as the method in the parent class. 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 method in the child class will be executed.In The end we can say that Having the same method in the subclass as declared in the parent class is known as Method Overriding 

 

Necessary Conditions For Method Overriding:-

        

  1. The argument list should be exactly the same as that of the overridden method.
  2. The return type should be the same or a subtype of the return type declared in the original overridden method in the superclass.
  3. 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.
  4. Instance methods can be overridden only if they are inherited by the subclass.
  5. A method declared final cannot be overridden.
  6. A method declared static cannot be overridden but can be re-declared.
  7. If a method cannot be inherited, then it cannot be overridden.
  8. A subclass within the same package as the instance’s superclass can override any superclass method that is not declared private or final.
  9. A subclass in a different package can only override the non-final methods declared public or protected.
  10. 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.
  11. Constructors cannot be overridden.

        Advantages Of Method Overriding:-

  1.  Method Overriding is used to provide specific implementation of a method that is already provided by its super class.
  2. Method Overriding is used for Runtime Polymorphism

Example Of Method Overriding:-

 

class A

{

int i;

A(int a, int b) 

{

i = a+b;

}

void add() 

{

System.out.println(“Sum of a and b is: ” + i);

}

}

class B extends A 

{

int j;

B(int a, int b, int c) 

{

super(a, b);

j = a+b+c;

}

void add() 

{

super.add();

System.out.println(“Sum of a, b and c is: ” + j);

}

}

class MethodOverriding 

{

public static void main(String args[]) 

{

B b = new B(10, 20, 30);

b.add();

}

}

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