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Page 1: Java Latest Interview Questions And Answers

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Page 2: Java Latest Interview Questions And Answers

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JAVA Latest Interview QuestionsBy

GarudaTrainings.com

Page 3: Java Latest Interview Questions And Answers

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You focus at the person asking you that query and think, I should know this! But at that time, you cannot quite keep in mind, and then punch yourself psychologically for not planning for your meeting. Good thing that is just a bogus situation and you are definitely going to be able to response that query and more when the time comes! The common organization choosing a JAVA developer is looking for someone who can system well beyond the stage trained in an starting JAVA category. Hiring managers ask concerns that are not actually stumpers, but are intended to generate a applicant's further information of the topic.

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

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Java is a high-level programming language originally developed by Sun Microsystems and released in 1995. Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX.

What do you know about Java?

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Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX/Linux like HP-Unix, Sun Solaris, Redhat Linux, Ubuntu, CentOS, etc.

What are the supported platforms by Java Programming Language?

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Some features include Object Oriented, Platform Independent, Robust, Interpreted, Multi-threaded

List any five features of Java?

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  It’s compiler generates an architecture-neutral object file format, which makes the compiled code to be executable on many processors, with the presence of Java runtime system.

Why is Java Architectural Neutral?

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Java uses Just-In-Time compiler to enable high performance. Just-In-Time compiler is a program that turns Java byte code, which is a program that contains instructions that must be interpreted into instructions that can be sent directly to the processor.

How Java enabled High Performance?

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It is designed to adapt to an evolving environment. Java programs can carry extensive amount of run-time information that can be used to verify and resolve accesses to objects on run-time.

Why Java is considered dynamic?

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When Java is compiled, it is not compiled into platform specific machine, rather into platform independent byte code. This byte code is distributed over the web and interpreted by virtual Machine (JVM) on whichever platform it is being run.

 What is Java Virtual Machine and how it is considered in context of Java’s platform independent feature?

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Variables defined inside methods, constructors or blocks are called local variables. The variable will be declared and initialized within the method and it will be destroyed when the method has completed.

What is a Local Variable

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These are variables declared with in a class, outside any method, with the static keyword.

What is a Class Variable

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Singleton class control object creation, limiting the number to one but allowing the flexibility to create more objects if the situation changes.

What is Singleton class?

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  Constructor gets invoked when a new object is created. Every class has a constructor. If we do not explicitly write a constructor for a class the java compiler builds a default constructor for that class.

What do you mean by Constructor?

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Default value of float and double data type in different as compared to C/C++. For float its 0.0f and for double it’s 0.0d

What is the default value of float and double data type in Java?

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This data type is used to save space in large arrays, mainly in place of integers, since a byte is four times smaller than an int.

When a byte data type is used?

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Java provides access modifiers to set access levels for classes, variables, methods and constructors. A member has package or default accessibility when no accessibility modifier is specified.

What do you mean by Access Modifier?

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Variables, methods and constructors which are declared protected in a super class can be accessed only by the subclasses in other package or any class within the package of the protected members' class.

What is protected access modifier?

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Java provides these modifiers for providing functionalities other than Access Modifiers, synchronized used to indicate that a method can be accessed by only one thread at a time.

What do you mean by synchronized Non Access Modifier?

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JVM, or the Java Virtual Machine, is an interpreter which accepts ‘Byte code’ 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 ‘Byte code’.

Byte code is a highly optimized set of computer instruction which could be executed by the Java Virtual Machine (JVM).

The translation into Byte code 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 Byte code, thereby making the Java Program ‘Platform Independent’.

What is JVM? Why is Java called the ‘Platform Independent Programming Language’?

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When asked typical JAVA  most start up 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.

What is the Difference between JDK and JRE?

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We are sure you must be well-acquainted with the JAVA Basic 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.

 What does the ‘static’ keyword mean?

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public class ExplainStatic {public static String name = "Look I am a static

variable";}

For example:

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public class Application {public static void main(String[] args) { System.out.println(ExplainStatic.name) }}

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

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We don’t create object of the class ExplainStatic to access the static variable. We directly use the class name itself: ExplainStatic.name

 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.

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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)

Float Double

What are the Data Types supported by Java? What is Auto boxing and Un boxing?

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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.

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

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String object is immutable. i.e , the value stored in the String object cannot be changed.

Consider the following code snippet: String myString = “Hello”;myString = myString + ” Guest”;

 What is the difference between STRINGBUFFER and STRING?

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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 String Buffer/StringBuilder objects than String objects.

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String str = “Be Happy With Your Salary.''str += “Because Increments are a myth";StringBuffer strbuf = new StringBuffer();strbuf.append(str);System.out.println(strbuf);

The Output of the code snippet would be: Be Happy

With Your Salary. Because Increments are a myth.

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This is a very important concept in OOP 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.

What is Function Over-Riding and Over-Loading in Java?

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public class Car { public static void main (String [] args) { Car a = new Car(); 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() } } class Car { public void start() { System.out.println("This is a Generic start to any Car"); } } class Ferrari extends Car { public void start() { System.out.println("Lets start the Ferrari and go out for a cool Party."); } }

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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.Varying the Data Type.

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class CalculateArea{ void Area(int length){System.out.println(length*2);} void Area(int length , int width)

{System.out.println(length*width);}  public static void main(String args[]){ CalculateArea obj=new CalculateArea(); obj.Area(10);   // Area of a Square obj.Area(20,20);  // Area of a Rectangle  }} 

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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.

What is Constructors, Constructor Overloading in Java and Copy-Constructor?

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ublic class Boss{ String name;   Boss(String input) { //This is the constructor name = "Our Boss is also known as : " + input; } public static void main(String args[]) { Boss p1 = new Boss("Super-Man"); }}

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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:

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public class Boss{ String name;  Boss(String input) { //This is the constructor name = "Our Boss is also known as : " + input; } Boss() { name = "Our Boss is a nice man. We don’t call him names.”; }public static void main(String args[]) { Boss p1 = new Boss("Super-Man"); Boss p2 = new Boss(); }}

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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.

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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.

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

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base class for an entire family of classes, declared in java.lang, that your program can instantiate and throw. Here’s a hierarchical

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Exception class structure:

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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 Out Of Memory Error (OOM), that may not be so easy to handle.

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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 Runtime Exception, 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.

What is the difference between Throw and Throws in Java Exception Handling (remember this queston?)

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public void myMethod() throws PRException{..} This means the super function calling the function should

be equipped to handle this exception.public void Callee(){ try{ myMethod();}catch(PRException ex){ ...handle Exception....}}

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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

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Try{if(age>100){throw new

AgeBarException(); //Customized ExceptioN}else{....}}}catch(AgeBarException ex){...handle Exception.....}

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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.

What is the Difference between byte stream and Character streams?

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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.

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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.

What are File Input Stream and File Output Stream ? Explain with an example to read and write into files.

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public class FileHandling { public static void main(String [ ] args) throws IOException { FileInputStream inputStream = new FileInputStream ("Input.txt") ; FileOutputStream outputStream = new FileOutputStream("Output.txt",true) ;   byte[] buffer = new byte[1024]; //For larger files we specify a buffer size which defines the chunks size for

data int bytesRead; while ((bytesRead = inputStream.read(buffer)) != -1) outputStream.write(buffer, 0, bytesRead); inputStream.close() ; outputStream.close() ; } } 

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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 File Reader 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.

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

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FileWriter : This class is used to write to character files. Creation of a File Writer 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 Print Writers, which provide better performance and higher-level, more flexible methods to write data.

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File file = new File("fileWrite2.txt"); FileWriter fw = new FileWriter(file); for(int i=0;i<10;i++){ fw.write("Soham is Just Awesome : "+i); fw.flush(); } fw.close(); Usage of FileWriter and FileReader used in conjunction is as

follows: int c; FileReader fread = new FileReader("xanadu.txt"); FileWriter fwrite = new FileWriter("characteroutput.txt"); while ((c = fread.read()) != -1) fwrite.write(c);

Usage of FileWriter can be explained as follows

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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 ().

 Explain the difference between ITERATOR AND ENUMERATION INTERFACE with example.

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Whereas in case of Enumeration:

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Simple Date Format 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 Simple Date Format for handling user dates. We of course aren’t expecting Java interviewees to be absolutely spectacular with the syntaxes. But a basic know-how of this class is mandatory.

 

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?

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public class CurrentSystemDate {public static void main(String[] args) { SimpleDateFormat sysForm = new SimpleDate-

Format("yyyy/MM/DD HH:mm:ss"); Date curdate= new Date(); 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.

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