Core Java - Polymorphism

What is Polymorphism?

● Polymorphism

– The ability of a reference variable to change behavior according to what object instance it is holding.

– This allows multiple objects of different subclasses to be treated as objects of a single super class, while automatically selecting the proper methods to apply to a particular object based on the subclass it belongs to.

Example: Polymorphism


● Given the parent class Person and the subclass Student of the previous examples, we add another subclass of Person which is Employee.
● Below is the class hierarchy for that

● Now suppose we have a getName method in our super class Person, and we override this method in

both Student and Employee subclass's

public class Student {

public String getName(){

System.out.println(“Student Name:” + name);

return name;

}

}

public class Employee {

public String getName(){

System.out.println(“Employee Name:” + name);

return name;

}

}

● Going back to our main method, when we try to call the getName method of the reference Person ref,

the getName method of the Student object will be called.

● Now, if we assign ref to an Employee object, the getName method of Employee will be called.

1 public static main( String[] args ) {

2

3 Student studentObject = new Student();

4 Employee employeeObject = new Employee();

5

6 Person ref = studentObject; //Person ref. points to a

7 // Student object

8

9 // getName() method of Student class is called

10 String temp= ref.getName();

11 System.out.println( temp );

12

13 ref = employeeObject; //Person ref. points to an

14 // Employee object

15

16 //getName() method of Employee class is called

17 String temp = ref.getName();

18 System.out.println( temp );

19 }

● Another example that illustrates polymorphism is when we try to pass a reference to methods as a

parameter

● Suppose we have a static method printInformation that takes in a Person reference as parameter.

public static printInformation( Person p ){

// It will call getName() method of the

// actual object instance that is passed

p.getName();

}

● We can actually pass a reference of type Employee and type Student to the printInformation method as long as it is a subclass of the Person class.

public static main( String[] args )

{

Student studentObject = new Student();

Employee employeeObject = new Employee();

printInformation( studentObject );

printInformation( employeeObject );

}