Polymarphism interview questions and answers in java

July 18, 2014

Polymorphism is one of the Oops concept and mostly used feature in java. The ability of an object to take more than one form is called Polymorphism. The most common use of polymorphism in OOPs occurs when a parent class reference is used to refer to a child class object.

It is impossible to know that the only possible way to access the object is through a reference variable. A reference variable can be of only one type. Once declared, the type of the reference variable cannot be changed.

A reference variable can refer to any object of its declared type or any subtype of its declared type. A reference variable can be declared as a class or interface.

Ex: Let's take a look into the below example

interface Vehicle{}

class Mileage {}

public class Car extends Mileage implements Vehicle{}

see the implementation of the above example,

package com.blogspot.javatbrains;

     interface Vehicle {
          void type();
     }

     class Milage {
          public void totalMilage() {
              System.out.println("Inside the Milage class");
          }
     }

     class Car extends Milage implements Vehicle {

          @Override
          public void type() {
              System.out.println("Vehicle type is car");
         }

         public void totalMilage() {
              System.out.println("Inside the Car class");
         }
    }

    public class Polymarphism {

          public static void main(String[] args) {
              Car car = new Car();
              Milage milage = car;
              Vehicle vehicle = car;
                 car.totalMilage();
                 car.type();
                 milage.totalMilage();
                 vehicle.type();
         }
    }

Interview Questions and Answers:

1. What is Polymorphism in java?

A: Polymorphism is a 'Greek' word. Poly means 'many', morphism means 'forms'. The ability to exist in different forms is called 'Polymorphism'.
Polymorphism is a characteristic of being able to assign a different meaning or usage to something in different context - specifically, to allow an entity such as a variable, a function, or an object to have more than one form.

2. How does java implements polymorphism?

A: Polymorphism manifest itself in java in the form of multiple methods having the same name.

In some cases, multiple methods have the same name, but different formal arguments list.
In other case, multiple methods have same name, same return types, and same formal arguments list.

3. Explain the different forms of polymorphism?

A: There are two types of polymorphism one is Compile-time polymorphism and other one is Runtime polymorphism. Compile-time polymorphism is method overloading. Runtime polymorphism using inheritance and interfaces.

Polymorphism manifest itself three distinct forms in java:

Method overloading
Method overriding through inheritance
Method overriding through java interface

4. What is Runtime polymorphism or dynamic method dispatch?

A: In java, Runtime polymorphism or dynamic method dispatch is a process in which a call to an overridden method is resolved at runtime rather then at compile-time. In this process an overridden method is called through the reference variable of a subclass. The determination of the method to be called is based on the object being referred to by the reference variable.

5. Can you explain Static binding with an example?

A: When type of the object is determined at compile-time is called static binding. If any of the private, static or final are there in a class that is static binding.

Here, is the example of the static binding,

public class Developer{
           private void doWork(){
                 System.out.println("Developer is doing work");
           }

           public static void main(String[] args){
                 Developer emp = new Developer();
                 emp.doWork();
           }
    }

6. Can you explain dynamic binding with an example?

A: When type of the object is determined at the time of Runtime, it is known as dynamic binding.

Here, is the example of dynamic binding,

public class Developer{
          void doWork(){
               System.out.println("Developer is doing work");
          }
     }

     public class Tester extends Developer{
          void doWork(){
              System.out.println("Tester is doing work");
          }
       
          public static void main(String[] args){
               Developer dev = new Tester();
               dev.doWork();
          }
    }

In the above example object type can't be determined the compiler, because the instance of Developer is also an instance of Tester. So, compiler doesn't know that's type, only it's base type.

7. What is mean by overloading and overriding in java?

A: Method overloading and overriding is most widely used concept in java programming. You need to go through this link which already present about overloading and overriding.

8. What is interface in java?

A: You can go through this link which already I posted about the interfaces.

If any of you are facing more than these questions in interview, please share with me through "Contact me here" gadget or drop me an email to "admin@javatbrains.com".

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Polymarphism interview questions and answers in java

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