Java Polymorphism

tutorial and example
tutorial and example

Polymorphism

The process of representing one form in multiple forms is known as Polymorphism.

Polymorphism is derived from 2 greek words: poly and morphs. The word “poly” means many and “morphs” means forms. So polymorphism means many forms.

Polymorphism is not a programming concept but it is one of the principal of OOPs. For many objects oriented programming language polymorphism principle is common but whose implementations are varying from one objects oriented programming language to another object oriented programming language.

Real life example of polymorphism

Suppose if you are in class room that time you behave like a student, when you are in market at that time you behave like a customer, when you at your home at that time you behave like a son or daughter, Here one person present in different-different behaviors.

How to achieve Polymorphism in Java?

Polymorphism can be achieved in two of the following ways:

  • Method Overloading(Compile time Polymorphism)
  • Method Overriding(Run time Polymorphism)

Polymorphism principal is divided into two sub principal they are:

  • Static or Compile time polymorphism
  • Dynamic or Runtime polymorphism

Static polymorphism in Java is achieved by method overloading and Dynamic polymorphism in Java is achieved by method overriding

Note: Java programming does not support static polymorphism because of its limitations and java always supports dynamic polymorphism.

Example of Runtime Polymorphism in Java

In below example we create two class Person an Employee, Employee class extends Person class feature and override walk() method. We are calling the walk() 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. Here method invocation is determined by the JVM not compiler, So it is known as runtime polymorphism.

Example of Polymorphism in Java

Output

Running fast…

Dynamic Binding

Dynamic binding always says create an object of base class but do not create the object of derived classes. Dynamic binding principal is always used for executing polymorphic applications.

The process of binding appropriate versions (overridden method) of derived classes which are inherited from base class with base class object is known as dynamic binding.

Advantages of dynamic binding along with polymorphism with method overriding are.

  • Less memory space
  • Less execution time
  • More performance

Static polymorphism

The process of binding the overloaded method within object at compile time is known as Static polymorphism due to static polymorphism utilization of resources (main memory space) is poor because for each and every overloaded method a memory space is created at compile time when it binds with an object. In C++ environment the above problem can be solve by using dynamic polymorphism by implementing with virtual and pure virtual function so most of the C++ developer in real worlds follows only dynamic polymorphism.

Dynamic polymorphism

In dynamic polymorphism method of the program binds with an object at runtime the advantage of dynamic polymorphism is allocating the memory space for the method (either for overloaded method or for override method) at run time.

The advantage of dynamic polymorphism is effective utilization of the resources, So Java always use dynamic polymorphism. Java does not support static polymorphism because of its limitation.

Form of Polymorphism

There are many form of polymorphism,

  • Polymorphism with class
  • Polymorphism in methods
  • Polymorphism in interface

Polymorphism with classes

Those Java classes that can pass more than one IS-A test is polymorphic in nature. All Java classes are derived from the object class so, its references can pass instanceof  operator test with the object class and its own object. So, we can conclude that all Java class is polymorphic.

We can access the objects in Java through reference variable. These reference variables can assign different objects (if reference is not declared final) also once declared, these references type cannot be changed.

The reference variable determines which method it can invoke on the object. The reference variable can be declared as a class or interface type. Reference variable can refer to any object of the declared type or its subtype.

Example:

Output:

In method Overriding, JRE decides which method is to invoke in run time, based on the exact type of the object on which the method is called.

Polymorphism in methods (Binding of variables and methods at compile time and runtime)

Binding refers to resolving of variables or methods that would be called for a reference variable. We use reference variable of a base class to refer to an object of a derived class.

But there is difference, instance variables bind at compile time while the methods bind at runtime.

Example:

Output:

System.out.println(b.name); will print Gopal since the reference variable is of type Parent. The field variable binds at the compile time.

b.displayName(); will print the name Rohan because JRE sees that the exact object is of type Child and have an overriding method displayName hence, JRE invoke the displayName of the Child Class.

Polymorphism with interfaces

We can implement polymorphism using interface also. We need a class which implements this interface.

Polymorphism with interfaces involves abstract or default methods of interface. Interface can also define static methods, but static methods never participate in polymorphism.

Example :

Output:

JRE dynamically calls the method of the corresponding object and executes their methods.