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Polymorphism:

Polymorphism is a Java concept that allows us to perform a single action in multiple ways. Polymorphism is made up of two Greek words: polymorphism and morphism. The words “poly” and “morphs” both mean “many.” Polymorphism denotes the presence of multiple forms.

Types of polymorphism:

• compile-time polymorphism
• runtime polymorphism.

Polymorphism in Java is achieved through method overloading and overriding.

Runtime Polymorphism in Java:

A call to an overridden method is resolved at runtime rather than compile-time in runtime polymorphism or Dynamic Method Dispatch.

In this process, a super class’s reference variable is used to call an overridden method. The object referred to by the reference variable is used to determine which method should be called.

Upcasting:

Upcasting occurs when a reference variable in the Parent class refers to an object in the Child class. For instance:

class A{}  
class B extends A{}  

A a=new B();//upcasting  

We can use the reference variable of class type or an interface type for upcasting. For Example:

interface I{}  
class A{}  
class B extends A implements I{}  

Here, the relationship of B class would be:

B IS-A A
B IS-A I
B IS-A Object

Since Object is the root class of all classes in Java, so we can write B IS-A Object.

Example:

class Car{  
  void run(){System.out.println("running");}  
 }  
class Honda extends Car{  
  void run()
 {
  System.out.println("running safely with 60km");
 }  
  
  public static void main(String args[]){  
    Car b = new Honda();//upcasting  
    b.run();  
  }  
}  

Output:

running safely with 60km.

Runtime polymorphism: shapes example

class Shape
{  
  void area()
   {
     System.out.println("area of a shape:");
   }  
}  
class Rectangle extends Shape
{  
   void area()
     {
       System.out.println("area of a rectangle:l*w");
     }  
}  
class Circle extends Shape
{  
   void area()
   {
     System.out.println("area of a circle: pi*r*r");
   }  
}  
class Triangle extends Shape
  {  
    void area()
    {
      System.out.println("area of a triangle:(b*h)/2");
    }  
}  
class TestPolymorphism2
 {  
    public static void main(String args[])
  {  
   Shape s;  
   s=new Rectangle();  
   s.area();  
   s=new Circle();  
   s.area();  
   s=new Triangle();  
   s.area();  
 }  
}  

Static binding & dynamic binding

• Binding is a mechanism that connects the method call and the actual implementation of the method.
• A Java object can have many forms thanks to the polymorphism concept.
• At both compile and run time, object forms can be resolved.
• Static binding occurs when the link between the method call and the method implementation is resolved at compile time, whereas dynamic binding occurs when the link is resolved at run time.
• Static binding uses the type of the class and fields to resolve binding, whereas dynamic binding uses the object.

Sr. No.	Key	Static Binding	Dynamic Binding
1	Basic	It is resolved at compile time	It is resolved at run time
2	Resolve mechanism	static binding use type of the class and fields	Dynamic binding uses object to resolve binding
3	Example	Overloading is an example of static binding	Method overriding is the example of Dynamic binding
4.	Type of Methods	private, final and static methods and variables uses static binding	Virtual methods use dynamic binding

Note: also read about the Method Overriding in Java

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