www.GarudaTrainings.com
www.GarudaTrainings.com
You focus at the person asking you that query and think, I
should know this! But at that time, you cannot quite keep
in mi...
Java is a high-level programming language originally
developed by Sun Microsystems and released in 1995. Java
runs on a va...
Java runs on a variety of platforms, such as Windows, Mac
OS, and the various versions of UNIX/Linux like HP-
Unix, Sun So...
Some features include Object Oriented, Platform
Independent, Robust, Interpreted, Multi-threaded
www.GarudaTrainings.com
It’s compiler generates an architecture-neutral object file
format, which makes the compiled code to be executable
on many...
Java uses Just-In-Time compiler to enable high
performance. Just-In-Time compiler is a program that
turns Java byte code, ...
It is designed to adapt to an evolving environment.
Java programs can carry extensive amount of run-time
information that ...
When Java is compiled, it is not compiled into
platform specific machine, rather into platform
independent byte code. This...
Variables defined inside methods, constructors or blocks
are called local variables. The variable will be declared
and ini...
These are variables declared with in a class, outside
any method, with the static keyword.
www.GarudaTrainings.com
Singleton class control object creation, limiting the
number to one but allowing the flexibility to create
more objects if...
Constructor gets invoked when a new object is created.
Every class has a constructor. If we do not explicitly
write a cons...
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...
This data type is used to save space in large arrays,
mainly in place of integers, since a byte is four times
smaller than...
Java provides access modifiers to set access levels for
classes, variables, methods and constructors. A member
has package...
Variables, methods and constructors which are
declared protected in a super class can be accessed
only by the subclasses i...
Java provides these modifiers for providing
functionalities other than Access
Modifiers, synchronized used to indicate tha...
 JVM, or the Java Virtual Machine, is an interpreter which accepts ‘Byte
code’ and executes it.
 Java has been termed as...
 When asked typical JAVA most start up Java
developers get confused with JDK and JRE. And
eventually, they settle for ‘an...
 We are sure you must be well-acquainted with
the JAVA Basic Now that we are settled with the initial
concepts, let’s loo...
public class ExplainStatic
{
public static String name = "Look I am a static variable";
}
www.GarudaTrainings.com
public class Application
{
public static void main(String[] args)
{
System.out.println(ExplainStatic.name)
}
}
www.GarudaT...
 We don’t create object of the class ExplainStatic to
access the static variable. We directly use the class
name itself: ...
 This is one of the most common and fundamental Java interview
questions. This is something you should have right at your...
 Autoboxing: The Java compiler brings about an automatic
transformation of primitive type (int, float, double etc.)
into ...
String object is immutable. i.e , the value stored in
the String object cannot be changed.
Consider the following code sni...
StringBuffer/StringBuilder objects are
mutable: StringBuffer/StringBuilder objects are
mutable; we can make changes to the...
 String str = “Be Happy With Your Salary.''
 str += “Because Increments are a myth";
 StringBuffer strbuf = new StringB...
 This is a very important concept in OOP and is a
must-know for every Java Programmer.
 Over-Riding: An override is a ty...
 public class Car {
 public static void main (String [] args) {
 Car a = new Car();
 Car b = new Ferrari(); //Car ref,...
Over-Loading:
Overloading is the action of defining multiple methods
with the same name, but with different parameters. It...
 class CalculateArea{
 void Area(int length){System.out.println(length*2);}
 void Area(int length , int width){System.o...
 Constructor: The sole purpose of having Constructors is to
create an instance of a class. They are invoked while creatin...
ublic class Boss{
String name; Boss(String input)
{ //This is the constructor
name = "Our Boss is also known as :
" + inpu...
Constructor overloading: passing different number and
type of variables as arguments all of which are private
variables of...
 public class Boss{
 String name;
 Boss(String input) { //This is the constructor
 name = "Our Boss is also known as :...
Copy Constructor: A copy constructor is a type of
constructor which constructs the object of the class
from another object...
 Anything that’s not Normal is an exception.
Exceptions are the customary way in Java to indicate to
a calling method tha...
base class for an entire family of classes, declared in
java.lang, that your program can instantiate and throw.
Here’s a h...
www.GarudaTrainings.com
 An Unchecked Exception inherits from RuntimeException
(which extends from Exception). The JVM treats
RuntimeException di...
Throws: A throws clause lists the types of exceptions
that a method might throw, thereby warning the
invoking method – ‘Du...
 public void myMethod() throws PRException
 {..}
 This means the super function calling the function should be eq
uippe...
Using the Throw: If the user wants to throw an
explicit Exception, often customized, we use the
Throw. The Throw clause ca...
 Try
 {
 if(age>100){throw new AgeBarException(); //Customiz
ed ExceptioN
 }else{
 ....}
 }
 }catch(AgeBarException...
Every JAVA Programmer deals with File Operations.
To generate User reports, send attachments through
mails and spill out d...
 byte stream : For reading and writing binary data, byte stream is
incorporated. Programs use byte streams to perform byt...
 FileInputStream : It contains the input byte from a
file and implements an input stream.
 FileOutputStream : It uses fo...
 public class FileHandling {
 public static void main(String [ ] args) throws IOException
 {
 FileInputStream inputStr...
FileReader : The FileReader class makes it possible to
read the contents of a file as a stream of characters. It
works muc...
FileWriter : This class is used to write to character files.
Creation of a File Writer is not dependent on the file
alread...
 File file = new File("fileWrite2.txt");
 FileWriter fw = new FileWriter(file);
 for(int i=0;i<10;i++){
 fw.write("Soh...
 Iterators allow the caller to remove elements from the
underlying collection during the iteration with well-
defined sem...
www.GarudaTrainings.com
www.GarudaTrainings.com
 Simple Date Format is one such concrete class which is
widely used by Java developers for parsing and
formatting of date...
 public class CurrentSystemDate {
 public static void main(String[] args) {
 SimpleDateFormat sysForm = new SimpleDateF...
www.GarudaTrainings.com
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Java Latest Interview Questions And Answers

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Java Latest Interview Questions And Answers

  1. 1. www.GarudaTrainings.com
  2. 2. www.GarudaTrainings.com
  3. 3. 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. www.GarudaTrainings.com
  4. 4. 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. www.GarudaTrainings.com
  5. 5. 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. www.GarudaTrainings.com
  6. 6. Some features include Object Oriented, Platform Independent, Robust, Interpreted, Multi-threaded www.GarudaTrainings.com
  7. 7. 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. www.GarudaTrainings.com
  8. 8. 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. www.GarudaTrainings.com
  9. 9. 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. www.GarudaTrainings.com
  10. 10. 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. www.GarudaTrainings.com
  11. 11. 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. www.GarudaTrainings.com
  12. 12. These are variables declared with in a class, outside any method, with the static keyword. www.GarudaTrainings.com
  13. 13. Singleton class control object creation, limiting the number to one but allowing the flexibility to create more objects if the situation changes. www.GarudaTrainings.com
  14. 14. 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. www.GarudaTrainings.com
  15. 15. 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 www.GarudaTrainings.com
  16. 16. 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. www.GarudaTrainings.com
  17. 17. 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. www.GarudaTrainings.com
  18. 18. 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. www.GarudaTrainings.com
  19. 19. 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. www.GarudaTrainings.com
  20. 20.  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’. www.GarudaTrainings.com
  21. 21.  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. www.GarudaTrainings.com
  22. 22.  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. www.GarudaTrainings.com
  23. 23. public class ExplainStatic { public static String name = "Look I am a static variable"; } www.GarudaTrainings.com
  24. 24. public class Application { public static void main(String[] args) { System.out.println(ExplainStatic.name) } } www.GarudaTrainings.com
  25. 25.  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. www.GarudaTrainings.com
  26. 26.  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 www.GarudaTrainings.com
  27. 27.  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 www.GarudaTrainings.com
  28. 28. 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”; www.GarudaTrainings.com
  29. 29. 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. www.GarudaTrainings.com
  30. 30.  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. www.GarudaTrainings.com
  31. 31.  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. www.GarudaTrainings.com
  32. 32.  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.");  }  } www.GarudaTrainings.com
  33. 33. 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. www.GarudaTrainings.com
  34. 34.  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  } } www.GarudaTrainings.com
  35. 35.  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. www.GarudaTrainings.com
  36. 36. 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"); } } www.GarudaTrainings.com
  37. 37. 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: www.GarudaTrainings.com
  38. 38.  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();  }  } www.GarudaTrainings.com
  39. 39. 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. www.GarudaTrainings.com
  40. 40.  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. www.GarudaTrainings.com
  41. 41. base class for an entire family of classes, declared in java.lang, that your program can instantiate and throw. Here’s a hierarchical www.GarudaTrainings.com
  42. 42. www.GarudaTrainings.com
  43. 43.  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.www.GarudaTrainings.com
  44. 44. 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. www.GarudaTrainings.com
  45. 45.  public void myMethod() throws PRException  {..}  This means the super function calling the function should be eq uipped to handle this exception.  public void Callee()  {  try{  myMethod();  }catch(PRException ex)  {  ...handle Exception....  }  } www.GarudaTrainings.com
  46. 46. 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 www.GarudaTrainings.com
  47. 47.  Try  {  if(age>100){throw new AgeBarException(); //Customiz ed ExceptioN  }else{  ....}  }  }catch(AgeBarException ex){  ...handle Exception.....  } www.GarudaTrainings.com
  48. 48. 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. www.GarudaTrainings.com
  49. 49.  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. www.GarudaTrainings.com
  50. 50.  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. www.GarudaTrainings.com
  51. 51.  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() ;  }  } www.GarudaTrainings.com
  52. 52. 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. www.GarudaTrainings.com
  53. 53. 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. www.GarudaTrainings.com
  54. 54.  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); www.GarudaTrainings.com
  55. 55.  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 (). www.GarudaTrainings.com
  56. 56. www.GarudaTrainings.com
  57. 57. www.GarudaTrainings.com
  58. 58.  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. www.GarudaTrainings.com
  59. 59.  public class CurrentSystemDate {  public static void main(String[] args) {  SimpleDateFormat sysForm = new SimpleDateFormat ("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. www.GarudaTrainings.com
  60. 60. www.GarudaTrainings.com

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