SECOND BLOG OF DSA:

Iqra Ghani
Nov 4 · 4 min read

Polymorphism in Java is a concept by which we can perform a single action in different ways. Polymorphism is derived from 2 Greek words: poly and morphs. The word “poly” means many and “morphs” means forms. So polymorphism means many forms.

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.

Compile time Polymorphism (or Static polymorphism)

Polymorphism that is resolved during compiler time is known as static polymorphism. Method overloading is an example of compile time polymorphism.
Method Overloading: This allows us to have more than one method having the same name, if the parameters of methods are different in number, sequence and data types of parameters.

Example of static Polymorphism

Method overloading is one of the way java supports static polymorphism. Here we have two definitions of the same method add() which add method would be called is determined by the parameter list at the compile time. That is the reason this is also known as compile time polymorphism.

class SimpleCalculator
{
int add(int a, int b)
{
return a+b;
}
int add(int a, int b, int c)
{
return a+b+c;
}
}
public class Demo
{
public static void main(String args[])
{
SimpleCalculator obj = new SimpleCalculator();
System.out.println(obj.add(10, 20));
System.out.println(obj.add(10, 20, 30));
}
}

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. The determination of the method to be called is based on the object being referred to by the reference variable.

Upcasting

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

  1. class A{}
  2. class B extends A{}
  3. A a=new B();//upcasting

For upcasting, we can use the reference variable of class type or an interface type. For Example:

  1. interface I{}
  2. class A{}
  3. class B extends A implements I{}

Here, the relationship of B class would be:

B IS-A A
B IS-A I
B IS-A Object

Since Object is the root class of all classes in Java, so we can write B IS-A Object.


Example of Java Runtime Polymorphism

In this example, we are creating two classes Bike and Splendor. Splendor class extends Bike 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, the subclass method is invoked at runtime.

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

Output:

running safely with 60km.

Java Runtime Polymorphism Example: Bank

Consider a scenario where Bank is a class that provides a method to get the rate of interest. However, the rate of interest may differ according to banks. For example, SBI, ICICI, and AXIS banks are providing 8.4%, 7.3%, and 9.7% rate of interest.

Output:

SBI Rate of Interest: 8.4
ICICI Rate of Interest: 7.3
AXIS Rate of Interest: 9.7

Java Runtime Polymorphism Example: Shape

Output:

drawing rectangle...
drawing circle...
drawing triangle...

BY 18SW20

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