1.
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What is Java?
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A high-level
programming language developed by Sun Microsystems. Java was originally
called OAK, and was designed for handheld devices and set-top boxes. Oak was
unsuccessful so in 1995 Sun changed the name to Java and modified the
language to take advantage of the burgeoning World Wide Web.
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2.
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what are the main
features of java?
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The main features of java are
§ Compiled and Interpreted
§ Object oriented
§ Robust and secure
§ Type safe
§ High Performance.
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3.
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What are pass by
reference and passby value?
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Pass By Reference
means the passing the address itself rather than passing the value. Passby
Value means passing a copy of the value to be passed.
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4.
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What is the Java
API?
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The Java API is a
large collection of ready-made software components that provide many useful
capabilities, such as graphical user interface (GUI) widgets.
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5.
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What is the Java
Virtual Machine (JVM)?
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The Java Virtual
Machine is software that can be ported onto various hardware-based platforms.
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6.
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What is variables
and then types?
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Variables is an identifier that denotes a
storage location used to store a data values.unlike constants that remain
unchanged during the execution of a program, a variable may takes different
values at different times during the execution of the program.
§ Instance variables
§ Class variables
§ Local variable
§ Parameters
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7.
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what is dot
operator?
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The dot operator(.) is
used to access the instance variables and methods of class objects.It is also
used to access classes and sub-packages from a package.
Examples : Person1.age ---------> Reference to the variable age |
8.
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Define strings?
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Strings represent a
sequence of characters.The easiest way to represent a sequence of characters
in java is by using a character array.
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9.
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What is
serialization?
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Serialization is the
process of converting a objects into a stream of bytes.
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10.
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What are different
types of access modifiers?
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Access specifiers are keywords that determine
the type of access to the member a class.
§ Public
§ Protected
§ Private
§ Default
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11.
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What is an abstract
class?
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Abstract class is a
class which contain one or more abstract methods, which has to be implemented
by sub classes. An abstract class can contain no abstract methods also i.e.
abstract class may contain concrete methods.
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12.
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what are class
variables
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Class variables are
global to a class and belong to the entire set of objects that class creates.
Only one memory location is created for each variable.
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13.
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What is the
Collection interface?
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The Collection
interface provides support for the implementation of a mathematical bag - an
unordered collection of objects that may contain duplicates.
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14.
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What must a class do
to implement an interface?
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The class must provide
all of the methods in the interface and identify the interface in its
implements clause.
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15.
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What is the
Collections API?
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The Collections API is
a set of classes and interfaces that support operations on collections of
objects.
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16.
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What is an array?
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Array is a group of
related data items that share a common name.For instance, we can define an
array name salary to represent a set of salaries of a group of employees.
Examples : salary[10] |
17.
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What is a list
iterator?
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The List and Set
collections provide iterators, which are objects that allow going over all
the elements of a collection in sequence. The java.util.Iterator interface provides for one-way traversal and
java.util.ListIterator is an iterator for lists that allows the programmer to
traverse the list in either direction (i.e. forward and or backward) and
modify the list during iteration.
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18
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What is the main
difference between a String and a StringBuffer class?
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String is immutable : you can’t modify a string
object but can replace it by creating a new instance. Creating a new instance
is rather expensive.
StringBuffer is mutable : use StringBuffer or StringBuilder when you want to modify the contents. StringBuilder was added in Java 5 and it is identical in all respects to StringBuffer except that it is not synchronized,which makes it slightly faster at the cost of not being thread-safe. |
19.
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When to use
serialization?
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A common use of
serialization is to use it to send an object over the network or if the state
of an object needs to be persisted to a flat file or a database.
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20.
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What is the main
difference between shallow cloning and deep cloning of objects?
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Java supports shallow
cloning of objects by default when a class implements the java.lang.Cloneable
interface.
Deep cloning through serialization is faster to develop and easier to maintain but carries a performance overhead. |
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21.
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What are wrapper
classes?
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primitive data types
may be converted into object types by using the wrapper classes contained in
the java.lang package.
Exampes : int, float, long, char, double |
22.
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What is the
difference between an instance variable and a static variable?
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Class variables are
called static variables. There is only one occurrence of a class variable per
JVM per class loader.When a class is loaded the class variables are initialized.
Instance variables are non-static and there is one occurrence of an instance variable in each class instance.Also known as a member variable or a field. |
23
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Where and how can
you use a private constructor?
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Private constructor is
used if you do not want other classes to instantiate the object and to
prevent subclassing.The instantiation is done by a public static method (i.e.
a static factory method) within the same class.
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24.
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What is type
casting?
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Type casting means
treating a variable of one type as though it is another type.
Examples : int m = 5; byte n =i; |
25.
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What is a user
defined exception?
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User defined
exceptions may be implemented by defining a new exception class by extending
the Exception class.
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26.
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What is an
instanceof operator?
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Instanceof is an
object reference operator and returns true if the object on the left-hand
side is an instance of the glass given to the right hand side.This operator
allows to determine whether the object belongs to a particular class or not.
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27.
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What are runtime
exceptions?
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Runtime exceptions are
those exceptions that are thrown at runtime because of either wrong input
data or because of wrong business logic etc. These are not checked by the
compiler at compile time.
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28
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What is the
difference between an interface and an abstract class?
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An abstract class may
contain code in method bodies, which is not allowed in an interface. With
abstract classes, you have to inherit your class from it and Java does not
allow multiple inheritance. On the other hand, you can implement multiple
interfaces in your class.
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29.
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what is a package?
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A package is a
namespace that organizes a set of related classes and interfaces.The classes
contained in the packages of other programs can be easily reused.Packages,
classes can be unique compared with classes in other packages.That is, two
classes in two different packages can have the same name.
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30.
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Why do threads block
on I/O?
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Threads block on i/o
(that is enters the waiting state) so that other threads may execute while
the i/o Operation is performed.
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31.
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What is the List
interface?
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The List interface
provides support for ordered collections of objects.
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32.
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What is the Vector
class?
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The Vector class
provides the capability to implement a growable array of objects.
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33
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What is the base
class of all classes?
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java.lang.Object
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34
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What is the
importance of static variable?
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static variables are
class level variables where all objects of the class refer to the same
variable. If one object changes the value then the change gets reflected in
all the objects.
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35.
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What is the
difference between a while statement and a do while statement?
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A while statement
checks at the beginning of a loop to see whether the next loop iteration
should occur. A do while statement checks at the end of a loop to see whether
the next iteration of a loop should occur. The do whilestatement will always
execute the body of a loop at least once.
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36.
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Describe life cycle
of thread?
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A thread is similiar to a program that has a
single flow of control.A thread is a execution in a program. The life cycle
of threads are
§ Newborn state
§ Runnable state
§ Running state
§ Blocked state
§ Dead state
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37.
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What is an Applets?
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Applets are small java
programs that are primarily used in Internet computing. They can be
transported over the internet from one computer to another and run using the
Applet Viewer or any web browser that supports java.
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38
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What are wrapped
classes?
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Wrapped classes are
classes that allow primitive types to be accessed as objects.
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39.
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What is the
difference between an if statement and a switch statement?
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The if statement is
used to select among two alternatives. It uses a boolean expression to decide
which alternative should be executed. The switch statement is used to select
among multiple alternatives. It uses an int expression to determine which
alternative should be executed.s
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40.
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What modifiers are
allowed for methods in an Interface?
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Only public and
abstract modifiers are allowed for methods in interfaces.
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41.
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What is the
difference between method overriding and overloading?
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Overriding is a method
with the same name and arguments as in a parent, whereas overloading is the
same method name but different arguments.
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42.
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What do you mean by
polymorphism?
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Polymorphism means the
ability to take more than one form. fro example, an operation may exhibit
behaviour in different instances. The behaviour depends upon the types of
data used in the operatiom.
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43
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What is the
difference between an abstract class and an interface?
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Abstract class Interface - Have executable methods and abstract
methods.Can only subclass one abstract class
Interface - Have no implementation code. All methods are abstract.A class can implement any number of interfaces. |
44.
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What is the purpose
of finalization?
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The purpose of
finalization is to give an unreachable object the opportunity to perform any
cleanup processing before the object is garbage collected.
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45.
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What is the
difference between a break statement and a continue statement?
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Break statement
results in the termination of the statement to which it applies (switch, for,
do, or while).
A Continue statement is used to end the current loop iteration and return control to the loop statement. |
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46.
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When is a method
said to be overloaded and when is a method said to be overridden?
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Overloading deals with
multiple methods in the same class with the same name but different method
signatures.
Overriding deals with two methods, one in the parent class and the other one in the child class and has the same name and signatures. |
47.
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How is final
different from finally and finalize()?
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§ Final - constant declaration.
§ The finally block always executes when the try
block exits, except System.exit(0) call.
§ finalize() is a method of Object class which
will be executed by the JVM just before garbage collecting object to give a
final chance for resource releasing activity.
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48.
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What is Byte Code?
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All Java programs are
compiled into class files that contain bytecodes. These byte codes can be run
in any platform and hence java is said to be platform independent.
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49.
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What is the
difference between error and an exception?
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Exception means When a
method encounters an abnormal condition (an exception condition) that it
can’t handle itself, it may throw an exception.
ssError mens system doesn’t handle.For example:Overflow,Out of memory. |
50.
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What if the main
method is declared as private?
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When a method is
declared as private, the program compiles properly but it will give runtime
error Main method not “public„.
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51.
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What type of
parameter passing does Java support?
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In Java the arguments
are always passed by value.
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52.
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What is singleton?
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It is one of the
design pattern. This falls in the creational pattern of the design pattern.
There will be only one instance for that entire JVM. You can achieve this by
having the private constructor in the class.
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53.
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What is Locale?
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A Locale object
represents a specific geographical, political, or cultural region.
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54.
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What is the
difference between constructors and normal methods?
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Constructors must have
the same name as the class and can not return a value. They are only called
once while regular methods could be called many times and it can return a
value or can be void.
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55.
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What is the
difference between static and non-static variables?
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A static variable is
associated with the class as a whole rather than with specific instances of a
class.
Non-static variables take on unique values with each object instance. |
56.
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What is the
difference between java and c++?
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§ Java is a true object - oriented language
while c++ is basically c with object-oriented extension.
§ C++ supports multiple inheritence but Java
provides interfaces in case of multiple inheritence.
§ Java does not support operator overloading.
§ Java does not have template classes as in c++.
§ java does not use pointers.
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