lPolymorphism in a Java program
-
- 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.
- Method overloading
- Method overriding through inheritance
- Method overriding through the Java interface
Example:
Given the parent class Person and the subclass Student of the previous examples, we add another subclass of Person which is Employee
lIn Java, we can create a reference that is of type super class to an object of its subclass. For example,
public static main( String[] args ) {
Student studentObject = new Student();
Employee employeeObject = new Employee();
Person ref = studentObject; // Person reference points // to a Student object
String name = ref.getName();
}
- 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;
}
}
l
- 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.
l
- Now, if we assign ref to an Employee object, the getName method of Employee will be called.
l
- Another example that illustrates polymorphism is when we try to pass a reference to methods as a parameter
l
- 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 );
}
