Java – Runtime Polymorphism

Runtime polymorphism:

• Runtime Polymorphism is a Method overriding technique.
• Defining a method in the Child class with the same name and same signature of its Parent class.
• We can implement Method overriding only in Parent-Child (Is-A) relation.

Child object shows the functionality(behavior) of Parent and Child is called Polymorphism

class Parent {             void behave(){                         System.out.println(“Parent behavior”);             } } class Child extends Parent {             void behave(){                         System.out.println(“Child behavior”);             }             void behavior(){                         super.behave();                         this.behave();             } } class Main {             public static void main(String[] args){                         Child child = new Child();                         child.behavior();             } }

Object Up-casting: We can store the address of Child class into Parent type reference variable.

Using parent address reference variable, we can access the functionality of Child class.

class Parent {             void fun(){                         System.out.println(“Parent’s functionality”);             } } class Child extends Parent {             void fun(){                         System.out.println(“Updated in Child”);             } } class Upcast {             public static void main(String[] args)  {                         Parent addr = new Child();                         addr.fun();             } }

Why it is calling Child functionality in the above application?

• Hostel address = new Student();
  • address.post();  ->  The Post reaches student
• Owner address = new Tenant();
  • address.post();  -> The Pose reaches tenant

Down casting: The concept of collecting Child object address back to Child type reference variable from Parent type.

When we use down-casting?

• Consider a method has to return object without knowing the class name, then it returns the address as Object.
• For example:
  • Object  getObject();
• As a programmer we collect the Object and convert into corresponding object type reference variable.
• For example:
  • Employee obj = (Employee)getObject();