Polymorphism in Java

The word polymorphism means having many forms. In simple words, we can define polymorphism as the ability of a message to be displayed in more than one form.

Real life example of polymorphism: A person at the same time can have different characteristic. Like a man at the same time is a father, a husband, an employee. So the same person posses different behaviour in different situations. This is called polymorphism.

Polymorphism is considered as one of the important features of Object Oriented Programming. Polymorphism allows us to perform a single action in different ways. In other words, polymorphism allows you to define one interface and have multiple implementations. The word “poly” means many and “morphs” means forms, So it means many forms.

In Java polymorphism is mainly divided into two types:

• Compile time Polymorphism
• Runtime Polymorphism

1. Compile time polymorphism: It is also known as static polymorphism. This type of polymorphism is achieved by function overloading or operator overloading.
   
   • Method Overloading: When there are multiple functions with same name but different parameters then these functions are said to be overloaded. Functions can be overloaded by change in number of arguments or/and change in type of arguments.
     1. Example: By using different types of argumentsclass MultiplyFun
        {// Method with 2 parameter
        static int Multiply(int a, int b)
        {
        return a * b;
        }// Method with the same name but 3 parameter
        static int Multiply(int a, int b, int c)
        {
        return a * b * c;
        }
        }class methodoverloading
        {
        public static void main(String[] args)
        {
        MultiplyFun mul=new MultiplyFun();System.out.println(MultiplyFun.Multiply(2, 4));
        System.out.println(MultiplyFun.Multiply(2, 7, 3));
        }
        }
     2. Example: By using different numbers of arguments// Java program for Method overloading class MultiplyFun { // Method with 2 parameter static int Multiply(int a, int b) { return a * b; } // Method with the same name but 2 double parameter static double Multiply(double a, double b) { return a * b; } } class methodoverloading2 { public static void main(String[] args) { System.out.println(MultiplyFun.Multiply(2, 4)); System.out.println(MultiplyFun.Multiply(5.5, 6.3)); } }
   • Operator Overloading: Java also provide option to overload operators. For example, we can make the operator (‘+’) for string class to concatenate two strings. We know that this is the addition operator whose task is to add two operands. So a single operator ‘+’ when placed between integer operands, adds them and when placed between string operands, concatenates them.In java, Only “+” operator can be overloaded:
     • To add integers
     • To concatenate strings
     Example:class OperatorOVERDDN
     {
     void operator(String str1, String str2)
     {
     String s = str1 + str2;
     System.out.println(“Concatinated String – “+ s);
     }
     void operator(int a, int b)
     {
     int c = a + b;
     System.out.println(“Sum = ” + c);
     }
     }
     class operatoroverloading
     {
     public static void main(String[] args)
     {
     OperatorOVERDDN obj = new OperatorOVERDDN();
     obj.operator(2, 3);
     obj.operator(“Ruchika “, “Katoch”);
     }
     }
2. Runtime polymorphism: It is also known as Dynamic Method Dispatch. It is a process in which a function call to the overridden method is resolved at Runtime. This type of polymorphism is achieved by Method Overriding.
   • Method overriding, on the other hand, occurs when a derived class has a definition for one of the member functions of the base class. That base function is said to be overridden.Example:class Parent
     {
     void Print()
     {
     System.out.println(“parent class”);
     }
     }
     class subclass1 extends Parent
     {
     void Print()
     {
     System.out.println(“subclass1”);
     }
     }class subclass2 extends Parent
     {
     void Print()
     {
     System.out.println(“subclass2”);
     }
     }class TestPolymorphism3
     {
     public static void main(String[] args)
     {subclass1 aa= new subclass1();
     aa.Print();
     subclass2 aa1= new subclass2();
     aa1.Print();
     }
     }No.Method OverloadingMethod Overriding1)Method overloading is used to increase the readability of the program.Method overriding is used to provide the specific implementation of the method that is already provided by its super class.2)Method overloading is performed within class.Method overriding occurs in two classes that have IS-A (inheritance) relationship.3)In case of method overloading, parameter must be different.In case of method overriding, parameter must be same.4)Method overloading is the example of compile time polymorphism.Method overriding is the example of run time polymorphism.5)In java, method overloading can’t be performed by changing return type of the method only. Return type can be same or different in method overloading. But you must have to change the parameter.Return type must be same or covariant in method overriding.