Runtime Polymorphism in Java
- Runtime Polymorphism
- Upcasting
- Example of Runtime
Polymorphism
- Runtime Polymorphism with
data members
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
When 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{}
1. A a=new B();//upcasting
Example of
Runtime Polymorphism
In this example, we are
creating two classes Bike and Splendar. Splendar 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, subclass method is invoked at
runtime.
Since method invocation is
determined by the JVM not compiler, it is known as runtime polymorphism.
1. class Bike{
2. void run(){System.out.println("running");}
3. }
4. class Splender extends Bike{
5. void run(){System.out.println("running safely with 60km");}
6.
7. public static void main(String args[]){
8. Bike b = new Splender();//upcasting
9. b.run();
10. }
11. }
Output:running safely with 60km.
Real example of Java Runtime Polymorphism
Consider a scenario,
Bank is a class that provides method to get the rate of interest. But, rate of
interest may differ according to banks. For example, SBI, ICICI and AXIS banks
could provide 8%, 7% and 9% rate of interest.
Note: It is also given in
method overriding but there was no upcasting.
1. class Bank{
2. int getRateOfInterest(){return 0;}
3. }
4.
5. class SBI extends Bank{
6. int getRateOfInterest(){return 8;}
7. }
8.
9. class ICICI extends Bank{
10. int getRateOfInterest(){return 7;}
11. }
12. class AXIS extends Bank{
13. int getRateOfInterest(){return 9;}
14. }
15.
16. class Test3{
17. public static void main(String args[]){
18. Bank b1=new SBI();
19. Bank b2=new ICICI();
20. Bank b3=new AXIS();
21. System.out.println("SBI Rate of Interest: "+b1.getRateOfInterest());
22. System.out.println("ICICI Rate of Interest: "+b2.getRateOfInterest());
23. System.out.println("AXIS Rate of Interest: "+b3.getRateOfInterest());
24. }
25. }
Output:
SBI Rate of Interest: 8
ICICI Rate of Interest: 7
AXIS Rate of Interest: 9
Runtime
Polymorphism with data member
|
Method
is overridden not the datamembers, so runtime polymorphism can't be achieved
by data members.
|
|
In
the example given below, both the classes have a datamember speedlimit, we
are accessing the datamember by the reference variable of Parent class which
refers to the subclass object. Since we are accessing the datamember which is
not overridden, hence it will access the datamember of Parent class always.
|
Rule:
Runtime polymorphism can't be achieved by data members.
1. class Bike{
2. int speedlimit=90;
3. }
4. class Honda3 extends Bike{
5. int speedlimit=150;
6.
7. public static void main(String args[]){
8. Bike obj=new Honda3();
9. System.out.println(obj.speedlimit);//90
10. }
Output:90
Runtime
Polymorphism with Multilevel Inheritance
Let's see the simple example of
Runtime Polymorphism with multilevel inheritance.
1. class Animal{
2. void eat(){System.out.println("eating");}
3. }
4.
5. class Dog extends Animal{
6. void eat(){System.out.println("eating fruits");}
7. }
8.
9. class BabyDog extends Dog{
10. void eat(){System.out.println("drinking milk");}
11.
12. public static void main(String args[]){
13. Animal a1,a2,a3;
14. a1=new Animal();
15. a2=new Dog();
16. a3=new BabyDog();
17.
18. a1.eat();
19. a2.eat();
20. a3.eat();
21. }
22. }
Output: eating
eating fruits
drinking Milk
Try for Output
1. class Animal{
2. void eat(){System.out.println("animal is eating...");}
3. }
4.
5. class Dog extends Animal{
6. void eat(){System.out.println("dog is eating...");}
7. }
8.
9. class BabyDog1 extends Dog{
10. public static void main(String args[]){
11. Animal a=new BabyDog1();
12. a.eat();
13. }}
Output: Dog is eating
Since, BabyDog is not
overriding the eat() method, so eat() method of Dog class is invoked.
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