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Meta: Don t go into your Java interview unprepared. Here are the top 15 Java interview questions that you might get during a job interview.

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Knowledge of these above mentioned oops interview questions can prove to be of immense help and can help you to crack the oops interview with flying colors.

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What is the difference between Throw and Throws in Java Exception Handling.

You stare at the person asking you that question and think, I should know this. But at that moment, you can t quite remember, and then kick yourself mentally for not preparing for your interview.

Good thing that s just a fake scenario and you re definitely going to be able to answer that question and more when the time comes.

The typical company hiring a Java programmer is looking for someone who can program well beyond the level taught in an introductory Java class. Interviewers ask questions that aren t necessarily stumpers, but are meant to elicit a candidate s deeper knowledge of the subject matter. While we would suggest you to learn Java thoroughly before facing an interview, this article will give you a special sneak peek into the Top 15 Java Interview Questions that one might confront during a job interview.

Let s start off with the easier questions and head out to the slightly tougher ones.

1. What is JVM. Why is Java called the Platform Independent Programming Language.

JVM, or the Java Virtual Machine, is an interpreter which accepts Bytecode and executes it.

Java has been termed as a Platform Independent Language as it primarily works on the notion of compile once, run everywhere. Here s a sequential step establishing the Platform independence feature in Java:

The Java Compiler outputs Non-Executable Codes called Bytecode.

Bytecode is a highly optimized set of computer instruction which could be executed by the Java Virtual Machine JVM.

The translation into Bytecode makes a program easier to be executed across a wide range of platforms, since all we need is a JVM designed for that particular platform.

JVMs for various platforms might vary in configuration, those they would all understand the same set of Bytecode, thereby making the Java Program Platform Independent.

2. What is the Difference between JDK and JRE.

When asked typical Java Interview Questions most startup Java developers get confused with JDK and JRE. And eventually, they settle for anything would do man, as long as my program runs.. Not quite right if you aspire to make a living and career out of Programming.

The JDK is the Java Development Kit. I.e., the JDK is bundle of software that you can use to develop Java based software.

The JRE is the Java Runtime Environment. I.e., the JRE is an implementation of the Java Virtual Machine which actually executes Java programs.

Typically, each JDK contains one or more JRE s along with the various development tools like the Java source compilers, bundling and deployment tools, debuggers, development libraries, etc.

3. What does the static keyword mean.

We are sure you must be well-acquainted with the Java Basics. Now that we are settled with the initial concepts, let s look into the Language specific offerings.

Static variable is associated with a class and not objects of that class. For example:

public static String name Look I am a static variable ;

We have another class where-in we intend to access this static variable just defined.

public static void main String args

System.out.println ExplainStatic.name

We don t create object of the class ExplainStatic to access the static variable. We directly use the class name itself: ExplainStatic.name

4. What are the Data Types supported by Java. What is Autoboxing and Unboxing.

This is one of the most common and fundamental Java interview questions. This is something you should have right at your finger-tips when asked. The eight Primitive Data types supported by Java are:

Byte : 8-bit signed two s complement integer. It has a minimum value of -128 and a maximum value of 127 inclusive

Short : 16-bit signed two s complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 inclusive.

Int : 32-bit signed two s complement integer. It has a minimum value of -2,147,483,648 and a maximum value of 2,147,483,647 inclusive

Long : 64-bit signed two s complement integer. It has a minimum value of -9,223,372,036,854,775,808 and a maximum value of 9,223,372,036,854,775,807 inclusive

Autoboxing: The Java compiler brings about an automatic transformation of primitive type int, float, double etc. into their object equivalents or wrapper type Integer, Float, Double,etc for the ease of compilation.

Unboxing: The automatic transformation of wrapper types into their primitive equivalent is known as Unboxing.

5. What is the difference between STRINGBUFFER and STRING.

String object is immutable. i.e, the value stored in the String object cannot be changed. Consider the following code snippet:

When you print the contents of myString the output will be Hello Guest. Although we made use of the same object myString, internally a new object was created in the process. That s a performance issue.

StringBuffer/StringBuilder objects are mutable: StringBuffer/StringBuilder objects are mutable; we can make changes to the value stored in the object. What this effectively means is that string operations such as append would be more efficient if performed using StringBuffer/StringBuilder objects than String objects.

String str Be Happy With Your Salary.

str Because Increments are a myth ;

StringBuffer strbuf new StringBuffer ;

The Output of the code snippet would be: Be Happy With Your Salary. Because Increments are a myth.

6. What is Function Over-Riding and Over-Loading in Java.

This is a very important concept in OOP Object Oriented Programming and is a must-know for every Java Programmer.

Over-Riding: An override is a type of function which occurs in a class which inherits from another class. An override function replaces a function inherited from the base class, but does so in such a way that it is called even when an instance of its class is pretending to be a different type through polymorphism. That probably was a little over the top. The code snippet below should explain things better.

public static void main String args

Car b new Ferrari ; //Car ref, but a Ferrari object

a.start ; // Runs the Car version of start

b.start ; // Runs the Ferrari version of start

System.out.println This is a Generic start to any Car ;

System.out.println Lets start the Ferrari and go out for a cool Party. ;

Over-Loading: Overloading is the action of defining multiple methods with the same name, but with different parameters. It is unrelated to either overriding or polymorphism. Functions in Java could be overloaded by two mechanisms ideally:

Varying the number of arguments.

void Area int length System.out.println length 2 ;

void Area int length, int width System.out.println length width ;

CalculateArea obj new CalculateArea ;

obj.Area 10 ;   // Area of a Square

obj.Area 20,20 ;  // Area of a Rectangle

7. What is Constructors, Constructor Overloading in Java and Copy-Constructor.

Constructors form the basics of OOPs, for starters.

Constructor: The sole purpose of having Constructors is to create an instance of a class. They are invoked while creating an object of a class. Here are a few salient features of Java Constructors:

Constructors can be public, private, or protected.

If a constructor with arguments has been defined in a class, you can no longer use a default no-argument constructor – you have to write one.

They are called only once when the class is being instantiated.

They must have the same name as the class itself.

They do not return a value and you do not have to specify the keyword void.

If you do not create a constructor for the class, Java helps you by using a so called default no-argument constructor.

Boss String input //This is the constructor

name Our Boss is also known as : input;

Constructor overloading: passing different number and type of variables as arguments all of which are private variables of the class. Example snippet could be as follows:

name Our Boss is a nice man. We don t call him names. ;

Copy Constructor: A copy constructor is a type of constructor which constructs the object of the class from another object of the same class. The copy constructor accepts a reference to its own class as a parameter.

Note: Java Doesn t support Copy Constructor. Nevertheless folks from C/C background often get confused when asked about Java Copy Constructors.

8. What is Java Exception Handling. What is the difference between Errors, Unchecked Exception and Checked Exception.

Anything that s not Normal is an exception. Exceptions are the customary way in Java to indicate to a calling method that an abnormal condition has occurred.

In Java, exceptions are objects. When you throw an exception, you throw an object. You can t throw just any object as an exception, however only those objects whose classes descend from Throwable. Throwable serves as the base class for an entire family of classes, declared in java.lang, that your program can instantiate and throw. Here s a hierarchical Exception class structure:

An Unchecked Exception inherits from RuntimeException which extends from Exception. The JVM treats RuntimeException differently as there is no requirement for the application-code to deal with them explicitly.

A Checked Exception inherits from the Exception-class. The client code has to handle the checked exceptions either in a try-catch clause or has to be thrown for the Super class to catch the same. A Checked Exception thrown by a lower class sub-class enforces a contract on the invoking class super-class to catch or throw it.

Errors members of the Error family are usually thrown for more serious problems, such as OutOfMemoryError OOM, that may not be so easy to handle.

Exception handling needs special attention while designing large applications. So we would suggest you to spend some time brushing up your Java skills.

9. What is the difference between Throw and Throws in Java Exception Handling remember this queston.

Throws: A throws clause lists the types of exceptions that a method might throw, thereby warning the invoking method – Dude. You need to handle this list of exceptions I might throw. Except those of type Error or RuntimeException, all other Exceptions or any of their subclasses, must be declared in the throws clause, if the method in question doesn t implement a try catch block. It is therefore the onus of the next-on-top method to take care of the mess.

public void myMethod throws PRException

This means the super function calling the function should be equipped to handle this exception.

Using the Throw: If the user wants to throw an explicit Exception, often customized, we use the Throw. The Throw clause can be used in any part of code where you feel a specific exception needs to be thrown to the calling method.

if age 100 throw new AgeBarException ; //Customized ExceptioN

10. What is the Difference between byte stream and Character streams.

Every Java Programmer deals with File Operations. To generate User reports, send attachments through mails and spill out data files from Java programs. And a sound knowledge on File Operation becomes even more important while dealing with Java questions.

byte stream : For reading and writing binary data, byte stream is incorporated. Programs use byte streams to perform byte input and output.

Performing InputStream operations or OutputStream operations means generally having a loop that reads the input stream and writes the output stream one byte at a time.

You can use buffered I/O streams for an overhead reduction overhead generated by each such request often triggers disk access, network activity, or some other operation that is relatively expensive.

Character streams: Character streams work with the characters rather than the byte. In Java, characters are stored by following the Unicode allows a unique number for every character conventions. In such kind of storage, characters become the platform independent, program independent, language independent.

11. What are FileInputStream and FileOutputStream. Explain with an example to read and write into files.

FileInputStream : It contains the input byte from a file and implements an input stream.

FileOutputStream : It uses for writing data to a file and also implements an output stream.

public static void main String args throws IOException

FileInputStream inputStream new FileInputStream Input.txt ;

FileOutputStream outputStream new FileOutputStream Output.txt, true ;

//For larger files we specify a buffer size which defines the chunks size for data

while bytesRead inputStream.read buffer . -1

outputStream.write buffer, 0, bytesRead ;

12. What are FileReader and FileWriter. Explain with an example to read and write into files.

FileReader : The FileReader class makes it possible to read the contents of a file as a stream of characters. It works much like the FileInputStream, except the FileInputStream reads bytes, whereas the FileReader reads characters. The FileReader is intended to read text, in other words. One character may correspond to one or more bytes depending on the character encoding scheme.The FileReader object also lets web applications asynchronously read the contents of files or raw data buffers stored on the user s computer, using File or Blob objects to specify the file or data to read.

FileWriter : This class is used to write to character files. Creation of a FileWriter is not dependent on the file already existing. FileWriter will create the file before opening it for output when you create the object. Its write methods allow you to write character s or Strings to a file. FileWriters are usually wrapped by higher-level Writer objects such as BufferedWriters or PrintWriters, which provide better performance and higher-level, more flexible methods to write data.

Usage of FileWriter can be explained as follows :

File file new File fileWrite2.txt ;

FileWriter fw new FileWriter file ;

fw.write Soham is Just Awesome : i ;

Usage of FileWriter and FileReader used in conjunction is as follows:

FileReader fread new FileReader xanadu.txt ;

FileWriter fwrite new FileWriter characteroutput.txt ;

13. What is the difference between ArrayList and LinkedList.

Please pay special attention as this is probably one of the most widely asked interview questions.

We aren t going to state the properties of each in this question. What we are looking for are the differences. The prime areas where the two stand apart are as follows :

Sequential access.The control traverses from the first node to reach the indexed node.

The LinkedList is implemented using nodes linked to each other. Each node contains a previous node link, next node link, and value, which contains the actual data

14. Explain the difference between ITERATOR AND ENUMERATION INTERFACE with example.

Iterators allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics.

Iterator actually adds one method that Enumeration doesn t have: remove .

Whereas in case of Enumeration:

15. What is the use of the SimpleDateFormat and how can you use it to display the current system date in yyyy/MM/DD HH:mm:ss format.

SimpleDateFormat is one such concrete class which is widely used by Java developers for parsing and formatting of dates. This is also used to convert Dates to String and vice-versa.

Literally every Enterprise level Java Application invariably uses the SimpleDateFormat for handling user dates. We ofcourse aren t expecting Java interviewees to be absolutely spectacular with the syntaxes. But a basic know-how of this class is mandatory.

public class CurrentSystemDate

SimpleDateFormat sysForm new SimpleDateFormat yyyy/MM/DD HH:mm:ss ;

System.out.println sysForm.format curdate ;

The best way to brush up your Java knowledge is to open up an eclipse and write loads of codes and sample programs. Get into the habit of remembering syntaxes and applying the best coding standards possible.

And there s your top 15. Best of luck on your interview.

1. Some Advanced Java Programming

2. Java Programming using Eclipse

3. Servlets and JSPs: Creating Web Applications With Java

4. Java Essentials for Android.

WCF Interview Questions with Answers. Check Now- How to Crack Infosys Interview Questions. Frequently Asked Oops Interview Questions; Share and.

Given below is some standardized. NET Interview Questions ranging from easy to difficult, important for cracking any. NET Interview.

Oops Interview Questions And Answers For 3 Years Experienced Top 50 C Interview Questions and Answers for freshers and experienced are below are below .

Wipro interview details: 1,784 interview questions and 1,784 interview reviews posted anonymously by Wipro interview candidates.

WCF, commonly known as Windows Communication Foundation, previously known as Indigo, is a runtime and a set of APIs application programming interface in the. NET Framework for building connected, service-oriented applications. Given below are some of the very important WCF Interview Questions both conceptual and textual essential for desired result in any interview.

The most common WCF Interview Questions

Ans: Windows Communication Foundation WCF is an SDK Software development kit for developing and deploying services on Windows. WCF provides a runtime environment for services, enabling you to expose CLR Common Language Runtime types as services, and to consume other services as CLR types.

WCF is part of. NET 3.0 and requires. NET 2.0, so it can only run on systems that support it.

Ans: The Contracts in WCF are:

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Ans: It describes the actual behavior or operation of the service at runtime. It is the relationship between Address, contract and Binding.

State the address syntax and the different formats of WCF transport scheme.

Ans: Address syntax of WCF transport scheme:

transport :// machine or domain :optional port format.

The address formats are as follow:

HTTP Address Format TCP Address Format

Name the three major points in WCF.

Ans: Address, Binding and Contract.

Check Now- How to Crack Infosys Interview Questions

WCF Interview Questions for Fresher s

Ans: A – Address Where : Hints us towards the direction of services, like URL Uniform Resource Locator.

B – Bindings How : This feature tells us how to find the services or using which protocols finds the services SOAP, HTTP, TCT etc.

C – Contracts What : Contracts are an agreement between the consumer and the service providers that explains what parameters the service expects and what value it returns.

Name the 3 types of transaction manager WCF supports.

Ans: Following are the 3 types of transaction manager WCF supports:

What are Duplex Contracts in WCF.

Ans: WCF Services can communicate with client through a called duplex messaging pattern commonly known as callback. Duplex messaging in WCF can be done over different transports, like TCP, Named Pipes and even HTTP. This is collectively known as Duplex Contracts in WCF.

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What is WCF- One Way Contract.

Ans: One Way Contract in WCF are methods/operations which are invoked on the service by the client or the server in which either of them do not expect a reply back.

Ex: If a client invokes a method on the service then it will not expect a reply back from the service.

What is InstanceContextMode in WCF.

This particular property value in WCF indicates creation of new service objects. Following are the 3 property values of InstanceContextMode:

Trick WCF Interview Questions for the experienced

Ans: A proxy is a class by which a service client can interact with the service. By the use of proxy in the client application one is able to call the different methods exposed by the service.

Mention 4 differences between XMLSerializer and the DataContractSerializer.

Ans: The points of differences are as follows:

DataContractSerializer is the default serializer for WCF, XML Serializer is not.

DataContractSerializer faster compared to XMLSerializer.

DataContractSerializer is basically for very small, simple subset of the XML info-set.

XMLSerializer is used for complex schemes whereas DataContractSerializer are used for comparatively simple schemes.

Check Now: Basic Java Interview Questions and Answers

What are the characteristics of WCF Data Contract.

Ans: Following are the characteristics of WCF Data Contract:

– A data contract is defined by using a Data Contract Attribute on a class or structure.

– Members of the data structure which will be used by the service need to be marked with the Data Member Attribute.

– Implementation of the same interface by different classes is made possible as only the selected members will be transferred between the service and the client.

Ans: The Output will redirect the page to 3.aspx.

Explanation- Try block will throw a redirect error but after execution of the catch box the control will pass to the finally block which will redirect the page to 3.aspx.