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16.what is Runtime polymorphism or Dynamic Method Dispatch

Runtime polymorphism or Dynamic Method Dispatch is a process in which a call to an overridden method is resolved at runtime rather than compile-time.

In this process, an overridden method is called through the reference variable of a superclass. The determination of the method to be called is based on the object being referred to by the reference variable.

Let's first understand the upcasting before Runtime Polymorphism.

Upcasting:-

When reference variable of Parent class refers to the object of Child class, it is known as upcasting. For example:

class A{}

class B extends A{}

A a=new B();//upcasting

 

Example of Runtime Polymorphism:-

In this example, we are creating two classes vehical and pulsor. pulsor class extends vehical class and overrides its run() method. We are calling the run method by the reference variable of Parent class. Since it refers to the subclass object and subclass method overrides the Parent class method, subclass method is invoked at runtime.

note: Since method invocation is determined by the JVM not compiler, it is known as runtime polymorphism

class vehical{

void run(){System.out.println("running");}

}

class pulsor extends vehical{

void run(){System.out.println("running safely with 60km");}

public static void main(String args[]){

vehical b = new pulsor(); //upcasting

b.run();

}

}

 

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