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 );
}
