Polymorphism
Real-life Illustration: Polymorphism
A person at the same time can have different characteristics. Like a man at the same time is a father, a husband, an employee. So the same person possesses different behavior in different situations. This is called polymorphism.
Types of polymorphism
In Java polymorphism is mainly divided into two types:
- Compile-time Polymorphism
- Runtime 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. 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
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
For upcasting, we can use the reference variable of class type or an interface type. For Example:
interface I{}
class A{}
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 ObjectSince Object is the root class of all classes in Java, so we can write B IS-A Object.
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.
Note: This example is also given in method overriding but there was no upcasting.
class Bank{
float getRateOfInterest(){return 0;}
}
class SBI extends Bank{
float getRateOfInterest(){return 8.4f;}
}
class ICICI extends Bank{
float getRateOfInterest(){return 7.3f;}
}
class AXIS extends Bank{
float getRateOfInterest(){return 9.7f;}
}
class TestPolymorphism{
public static void main(String args[]){
Bank b;
b=new SBI();
System.out.println(“SBI Rate of Interest: “+b.getRateOfInterest());
b=new ICICI();
System.out.println(“ICICI Rate of Interest: “+b.getRateOfInterest());
b=new AXIS();
System.out.println(“AXIS Rate of Interest: “+b.getRateOfInterest());
}}
Output:
SBI Rate of Interest: 8.4
ICICI Rate of Interest: 7.3
AXIS Rate of Interest: 9.7Possibility of downcasting with instanceof
Let’s see the example, where downcasting is possible by instanceof operator.
class Animal { }
class Dog3 extends Animal {
static void method(Animal a) {
if(a instanceof Dog3){
Dog3 d=(Dog3)a;//downcasting
System.out.println(“ok downcasting performed”);
}}public static void main (String [] args) {
Animal a=new Dog3();
Dog3.method(a);
}}
Method Overloading: changing no. of arguments
In this example, we have created two methods, first add() method performs addition of two numbers and second add method performs addition of three numbers.
In this example, we are creating static methods so that we don’t need to create instance for calling methods.
class Adder{
static int add(int a,int b){return a+b;}
static int add(int a,int b,int c){return a+b+c;}
}
class TestOverloading1{
public static void main(String[] args){
System.out.println(Adder.add(11,11));
System.out.println(Adder.add(11,11,11));
}}
A real example of Java Method Overriding
Consider a scenario where Bank is a class that provides functionality to get the rate of interest. However, the rate of interest varies according to banks. For example, SBI, ICICI and AXIS banks could provide 8%, 7%, and 9% rate of interest.
Java method overriding is mostly used in Runtime Polymorphism which we will learn in next pages.
//Java Program to demonstrate the real scenario of Java Method Overriding
//where three classes are overriding the method of a parent class.
//Creating a parent class.
class Bank{
int getRateOfInterest(){return 0;}
}
//Creating child classes.
class SBI extends Bank{
int getRateOfInterest(){return 8;}
}
class ICICI extends Bank{
int getRateOfInterest(){return 7;}
}
class AXIS extends Bank{
int getRateOfInterest(){return 9;}
}
//Test class to create objects and call the methods
class Test2{
public static void main(String args[]){
SBI s=new SBI();
ICICI i=new ICICI();
AXIS a=new AXIS();
System.out.println(“SBI Rate of Interest: “+s.getRateOfInterest());
System.out.println(“ICICI Rate of Interest: “+i.getRateOfInterest());
System.out.println(“AXIS Rate of Interest: “+a.getRateOfInterest());
}
}
