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JAVA INTERVIEW QUESTIONS
http://www.tutorialspoint.com/java/java_interview_questions.htm
Copyright © tutorialspoint.com
Dear readers, these
Java Interview Questions
have been designed especially to get you
acquainted with the nature of questions you may encounter during your interview for
the subject of
Java Programming Language.
As per my experience, good interviewers
hardly planned to ask any particular question during your interview, normally
questions start with some basic concept of the subject and later they continue based
on further discussion and what you answer:
Q: What do you know about Java?
A:
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.
Q: What are the supported platforms by Java Programming Language?
A:
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.
Q: List any five features of Java?
A:
Some features include Object Oriented, Platform Independent, Robust, Interpreted,
Multi-threaded
Q: Why is Java Architectural Neutral?
A:
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.
Q: How Java enabled High Performance?
A:
Java uses Just-In-Time compiler to enable high performance. Just-In-Time compiler
is a program that turns Java bytecode, which is a program that contains instructions
that must be interpreted into instructions that can be sent directly to the processor.
Q: Why Java is considered dynamic?
A:
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.
Q: What is Java Virtual Machine and how it is considered in context of Java’s
platform independent feature?
A:
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.
Q: List two Java IDE’s?
A:
Netbeans, Eclipse, etc.
Q: List some Java keywords(unlike C, C++ keywords)?
A:
Some Java keywords are import, super, finally, etc.
Q: What do you mean by Object?
A:
Object is a runtime entity and it’s state is stored in fields and behavior is shown via
methods. Methods operate on an object's internal state and serve as the primary
mechanism for object-to-object communication.
Q: Define class?
A:
A class is a blue print from which individual objects are created. A class can contain
fields and methods to describe the behavior of an object.
Q: What kind of variables a class can consist of?
A:
A class consist of Local variable, instance variables and class variables.
Q: What is a Local Variable
A:
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.
Q: What is a Instance Variable
A:
Instance variables are variables within a class but outside any method. These
variables are instantiated when the class is loaded.
Q: What is a Class Variable
A:
These are variables declared with in a class, outside any method, with the static
keyword.
Q: What is Singleton class?
A:
Singleton class control object creation, limiting the number to one but allowing the
flexibility to create more objects if the situation changes.
Q: What do you mean by Constructor?
A:
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.
Q: List the three steps for creating an Object for a class?
A:
An Object is first declared, then instantiated and then it is initialized.
Q: What is the default value of byte datatype in Java?
A:
Default value of byte datatype is 0.
Q: What is the default value of float and double datatype in Java?
A:
Default value of float and double datatype in different as compared to C/C++. For
float its 0.0f and for double it’s 0.0d
Q: When a byte datatype is used?
A:
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.
Q: What is a static variable?
A:
Class variables also known as static variables are declared with the static keyword in
a class, but outside a method, constructor or a block.
Q: What do you mean by Access Modifier?
A:
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.
Q: What is protected access modifier?
A:
Variables, methods and constructors which are declared protected in a superclass
can be accessed only by the subclasses in other package or any class within the
package of the protected members' class.
Q: What do you mean by synchronized Non Access Modifier?
A:
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.
Q: According to Java Operator precedence, which operator is considered to be with
highest precedence?
A:
Postfix operators i.e () [] . is at the highest precedence.
Q: Variables used in a switch statement can be used with which datatypes?
A:
Variables used in a switch statement can only be a byte, short, int, or char.
Q: When parseInt() method can be used?
A:
This method is used to get the primitive data type of a certain String.
Q: Why is String class considered immutable?
A:
The String class is immutable, so that once it is created a String object cannot be
changed. Since String is immutable it can safely be shared between many threads
,which is considered very important for multithreaded programming.
Q: Why is StringBuffer called mutable?
A:
The String class is considered as immutable, so that once it is created a String object
cannot be changed. If there is a necessity to make alot of modifications to Strings of
characters then StringBuffer should be used.
Q: What is the difference between StringBuffer and StringBuilder class?
A:
Use StringBuilder whenever possible because it is faster than StringBuffer. But, if
thread safety is necessary then use StringBuffer objects.
Q: Which package is used for pattern matching with regular expressions?
A:
java.util.regex package is used for this purpose.
Q: java.util.regex consists of which classes?
A:
java.util.regex consists of three classes: Pattern class, Matcher class and
PatternSyntaxException class.
Q: What is finalize() method?
A:
It is possible to define a method that will be called just before an object's final
destruction by the garbage collector. This method is called finalize( ), and it can be
used to ensure that an object terminates cleanly.
Q: What is an Exception?
A:
An exception is a problem that arises during the execution of a program. Exceptions
are caught by handlers positioned along the thread's method invocation stack.
Q: What do you mean by Checked Exceptions?
A:
It is an exception that is typically a user error or a problem that cannot be foreseen
by the programmer. For example, if a file is to be opened, but the file cannot be found,
an exception occurs. These exceptions cannot simply be ignored at the time of
compilation.
Q: Explain Runtime Exceptions?
A:
It is an exception that occurs that probably could have been avoided by the
programmer. As opposed to checked exceptions, runtime exceptions are ignored at the
time of compliation.
Q: Which are the two subclasses under Exception class?
A:
The Exception class has two main subclasses : IOException class and
RuntimeException Class.
Q: When throws keyword is used?
A:
If a method does not handle a checked exception, the method must declare it using
the throwskeyword. The throws keyword appears at the end of a method's signature.
Q: When throw keyword is used?
A:
An exception can be thrown, either a newly instantiated one or an exception that
you just caught, by using throw keyword.
Q: How finally used under Exception Handling?
A:
The finally keyword is used to create a block of code that follows a try block. A finally
block of code always executes, whether or not an exception has occurred.
Q: What things should be kept in mind while creating your own exceptions in Java?
A:
While creating your own exception:
All exceptions must be a child of Throwable.
If you want to write a checked exception that is automatically enforced by the
Handle or Declare Rule, you need to extend the Exception class.
You want to write a runtime exception, you need to extend the
RuntimeException class.
Q: Define Inheritance?
A:
It is the process where one object acquires the properties of another. With the use of
inheritance the information is made manageable in a hierarchical order.
Q: When super keyword is used?
A:
If the method overrides one of its superclass's methods, overridden method can be
invoked through the use of the keyword super. It can be also used to refer to a hidden
field
Q: What is Polymorphism?
A:
Polymorphism is the ability of an object to take on many forms. The most common
use of polymorphism in OOP occurs when a parent class reference is used to refer to a
child class object.

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