Java Interview Questions and Answers
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What is a cloneable
interface and how many methods does it contain?-
It is not having any method because it is a TAGGED or MARKER interface.
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What is the difference
between abstract class and interface?-
a) All the methods declared inside an interface are abstract whereas abstract
class must have at least one abstract method and others may be concrete or
abstract. b) In abstract class, key word abstract must be used for the methods
whereas interface we need not use that keyword for the methods. c) Abstract
class must have subclasses whereas interface can’t have subclasses.
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Can you have an inner
class inside a method and what variables can you access?-
Yes, we can have an inner class inside a method and final variables can be
accessed.
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What is the difference
between String and String Buffer?-
a) String objects are constants and immutable whereas StringBuffer objects are
not. b) String class supports constant strings whereas StringBuffer class
supports growable and modifiable strings.
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What is the difference
between Array and vector?-
Array is a set of related data type and static whereas vector is a growable
array of objects and dynamic.
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What is the difference
between exception and error?-
The exception class defines mild error conditions that your program encounters.
Exceptions can occur when trying to open the file, which does not exist, the
network connection is disrupted, operands being manipulated are out of
prescribed ranges, the class file you are interested in loading is missing. The
error class defines serious error conditions that you should not attempt to
recover from. In most cases it is advisable to let the program terminate when
such an error is encountered.
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What is the difference
between process and thread?-
Process is a program in execution whereas thread is a separate path of
execution in a program.
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What is multithreading
and what are the methods for inter-thread communication and what is the class
in which these methods are defined?-
Multithreading is the mechanism in which more than one thread run independent
of each other within the process. wait (), notify () and notifyAll() methods
can be used for inter-thread communication and these methods are in Object
class. wait() : When a thread executes a call to wait() method, it surrenders
the object lock and enters into a waiting state. notify() or notifyAll() : To
remove a thread from the waiting state, some other thread must make a call to
notify() or notifyAll() method on the same object.
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What is the class and
interface in java to create thread and which is the most advantageous method?-
Thread class and Runnable interface can be used to create threads and using
Runnable interface is the most advantageous method to create threads because we
need not extend thread class here.
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What are the states
associated in the thread?-
Thread contains ready, running, waiting and dead states.
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What is synchronization?-
Synchronization is the mechanism that ensures that only one thread is accessed
the resources at a time.
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When you will
synchronize a piece of your code?-
When you expect your code will be accessed by different threads and these
threads may change a particular data causing data corruption.
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What is deadlock?-
When two threads are waiting each other and can’t precede the program is said
to be deadlock.
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What is daemon thread
and which method is used to create the daemon thread?-
Daemon thread is a low priority thread which runs intermittently in the back
ground doing the garbage collection operation for the java runtime system.
setDaemon method is used to create a daemon thread.
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Are there any global
variables in Java, which can be accessed by other part of your program?-
No, it is not the main method in which you define variables. Global variables
is not possible because concept of encapsulation is eliminated here.
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