Polymarphism interview questions and answers in java

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

1
2
3
4
5
interface Vehicle{}

class Mileage {}

public class Car extends Mileage implements Vehicle{}

see the implementation of the above example,

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
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,

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
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,

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
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".

 Do you know?
Location: Bengaluru, Karnataka 560017, India

Comments

Post a Comment

Popular posts from this blog

Hibernate auto increment with example

In previous example we learn how to map java object with database table for manually(not using auto increment) assigned all the values.  To create primary key auto increment application by using hibernate mapping(hbm.xml) or using annotations continue reading this article.  W e need to create a database and create an employee table by using the below query. Table: CREATE table EMPLOYEE( eid integer ( 10 ) primary key not null , firstname varchar ( 30 ), lastname varchar ( 30 ), designation varchar ( 30 ), salary double( 10 , 2 )); Here, we will create a bean/POJO (Plain Old Java Object) class of employee. Employee.java: package com . javatbrains . hibernate ; import java.io.Serializable ; /*This is the POJO class. It contains only Getter and Setter methods*/ public class Employee implements Serializable { private static final long serialVersionUID = - 75885815725314443L ; private int eid ; ...
Read more

how to count the page views by using JSP

To count no.of page's are viewed by user in your application is a challenge in real time application. In this page we will see how to count the page views when user has viewed the page.           Here, we will do one example how many times user has visited each page in our application. In this post we will come to know, how to count the total application page views as well as individually each pages count.           Let us assume my web application name is "Page Counter". For creating the web application in eclipse IDE, Click here . This Page Counter contains three pages, assume that are the different pages in an application. But, there is the link between each other files for navigating from one page to another. Also it will show the total pages view count and individual page view count in all the pages. Let us see, below is my first jsp file,         ...
Read more

Multithreading in java with example

Multithreading  is one of the most important concept in core java. In this article we will learn what is multithreading? , what is the use of it? and What is the use of Synchronization and when to use it?  with detailed examples. At a time, two or more threads are accessing the same object is called as Multithreading  in Java .  First, we will create two threads for two objects. It is also possible to run two or more threads on a single class object. In this case, there is a possibility to get unreliable results. If the two threads are perform same task, then they need same object to be executed each time. For your better understanding, take an example of any reservations like, railway, movie ticket booking,etc. Let us think only one berth is available in a train and two passengers are asking for that berth. The first person has sent a request to allocate that ticket/berth to him. At the same time, the second person also sent a request to allocate that ...
Read more

How to retrieve data from table by using JDBC with example

To retrieve data from mysql data table by using jdbc, we need to confirm weather which table data we need to retrieve. To confirm open your mysql and view all database names by using the ' show databases ' commands in mysql. Then select which is your database name from showing list of database names, by using the ' use <database name> ' command in mysql. Then we need to see all your existing tables by executing the ' show tables ' command. This command gives you the list of existing tables in your selected database. You need to use existing table only you can follow with that. But, here we will see with entirely new which is not existing in mysql database. Now, We will create simple mysql table with minimal columns. create table emp(eno integer(10), ename varchar(30), sal float); The above command creates a new table, we will move further to insert records into emp table by executing the insert which we mentioned in the below. ...
Read more

Prime, Fibonacci and Factorial number with example in java

Prime number, Fibonacci series and Factorial number programs are most commonly asked questions in interview. Read this article to know what is and how to write programs for prime number, fibonacci series and factorial number. Prime Number: prime number is natural number greater than 1 that has no positive divisor other than 1 and itself. A natural number greater than 1 is not a prime number, is called Composite number . For example, 7 is a prime number. Because it can divide with 1 and 7 only. Where as 8 is composite number. Since it has the divisor 2 and 4 in addition to the 1 and 8. The below example represents the finding the passing number is prime number or not. If the passing number is prime number it will print true otherwise it will print false. package com . javatbrains . practice ; public class PrimeNumber { public boolean isPrimeNumber ( int number ) { if ( number <= 1 ) return false ; // There's only one ...
Read more

How to insert images into database using JDBC?

How to insert images into database table by using JDBC? To know about these topic follow the below lines,           Before going to write a JDBC program for inserting images into database table, we need to create a specific table for inserting images column datatype. For creating the database table, execute the below command in MySQL command prompt. 1 2 3 4 CREATE TABLE ` images ` ( ` image_id ` int ( 11 ) NOT NULL AUTO_INCREMENT, ` image_flag ` int ( 11 ) NOT NULL , ` image ` longblob NOT NULL , PRIMARY KEY ( ` image_id ` ));           After executing the above query in MySQL command prompt, execute the below query to know weather the above table query is created or not. 1 Show tables;            When you have executed the above query that will show you the list of table which all exists in the current database. Current tab...
Read more

How to sort list of objects in java with examples

We could achieve list of objects sorting in java by using sort() method which is available under Collections class as well as by using Comparable and Comparator  interfaces. Comparable and Comparator are two interfaces in java used to sort list of objects. These interfaces are available under java.util package along with Collections  class and other classes and interfaces. Comparable interface contains the method of       public int compareTo(Object obj) Comparator interface contains the method of       public int compare(Object obj1, Object obj2) The compare() and compareTo() methods will return negative integer(-1), or zero(0) or positive integer(1). When the first obj1 is less than obj2 method will return negative integer. When obj1 is equals to obj2 will return zero and when obj1 is grater than obj2 it will return positive integer. If it's objects are stored in any Collection classes like ArrayList, H...
Read more

String interview questions and answers

String interview questions and answers are placed the current post as of my experience in interviews. This will helps who are trying to attend interview as fresher as well as experience. If any one is facing any other questions which are not present in the current page, please drop me an email to " subbareddynallamachu@gmail.com ".  Q1:  String is a class or data type? A: String is a class in java.lang package. But, in java, all classes are also are considered as data types. So we can take String as data type also. Q2:  What is the difference between == and equals() methods in java? A: == operator compares the references of the String object. It does not compare the content of the object. equals() method compares the contents. While comparing the Strings, equals method should be used as it yields the correct result. Q3:  What is String constant pool? A: String constant pool is a separate block of memory where the String objects are held by JVM....
Read more

Exception in thread "main" java.lang.NoClassDefFoundError: javax/transaction/SystemException

Exception in thread "main" java.lang.NoClassDefFoundError: javax/transaction/SystemException error we got in Hibernate 4.3 to work with my MySQL database. We are using hibernate code generation tool in Eclipse and we are able to connect to the database using the Hibernate configuration file. When we try to run code in my Main class application is connecting to the database, but transaction is failing and we got the following error: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Exception in thread "main" java . lang . NoClassDefFoundError : javax / transaction / SystemException at java . lang . Class . forName0 ( Native Method ) at java . lang . Class . forName ( Unknown Source ) at org . jboss . logging . Logger . getMessageLogger ( Logger . java : 2248 ) at org . jboss . logging . Logger . getMessageLogger ( Logger . java : 2214 ) at org . hibernate . cfg . Configuration .< clinit >( Configuration . java : 184 ) at be . comp . permanenti...
Read more

Store file into table by using JDBC with example

To store large data files or text files into database table, we will use CLOB (Charecter Large Object) datatype of SQL . By using CLOB it is possible to save entire text book or a file or resume into a column of data table. If your using MySQL database instead of CLOB use LONGTEXT to save file into datatable. For saving files into a data table, we need to create one table which will contains a column type as CLOB to store files. Here, is the query to create a data table. 1 2 3 4 create table myfiles( file_id int ( 10 ), file_name varchar ( 30 ), file_type LONGTEXT); Once table creation completes, these table contains the 3 columns one is file_id represents the file id, file_name represents the name of the file and finally file_type will get save entire file into the table column. Now, we will move to write a JDBC program which will saves the file into the newly creating table. Here is the JDBC program, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16...
Read more