Polymorphism in Java is a concept by which we can perform a single action in different ways.


There are two types of polymorphism in Java: compile-time polymorphism and runtime polymorphism. We can perform polymorphism in java by method overloading and method overriding.

If you overload a static method in Java, it is the example of compile time polymorphism.

Runtime Polymorphism in Java

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.

 Let's first understand the upcasting before Runtime Polymorphism.


Upcasting

If the 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 Java Runtime Polymorphism

In this example, we are creating two classes Bike and Splendor. Splendor class extends Bike class and overrides it's run() method. We are calling the run method by the reference variable of Parent class. Since it refers to the subclass object and the subclass method overrides the Parent class method, the subclass method is invoked at runtime.
Since method invocation is determined by the JVM not compiler, it is known as runtime polymorphism.

Class Bike{
void run()
{
System.ou.println(“running”);
}
}
Class Splendor extends Bike{
void run()
{System.ou.println(“running safely with 60km”);
}
public staic void main(String args[])
{
Bike b = new Splendor();//upcasting
b.run();
}
}