- What is bytecode?
Bytecode is a highly
optimized set of instructions designed to be executed by the java run-time
system. Which is called the java virtual machine (JVM). JVM is an interpreter
for bytecode.
- What is a Literal? What are the
different types of literals?
A Literal
represents a value of a certain type where the type describes the behaviors of
the value. The different types of literals are:
- Number literals
- Character literals
- Boolean literals
- String literals
- What is a Number literals?
There are several integer
literals as int, long, octal, hexadecimal etc. 10 is an example of a decimal
integer literal of type int. If a decimal integer literal is larger
that the int, it is declared to be of type long. A number can be
made long by appending L or 1 to it. Negative integers are preceded by
the minus sign. These integers can also be expressed as octal or hexadecimal. A
leading 0 to the integer indicate that the number is an octal integer. For
example, 0987 is an octal integer. A leading 0x to the integer indicate that
the number is a hexadecimal integer, example 0xaf94 is a hexadecimal number.
- What is a Character literals?
Character literals are
expressed by a single character enclosed within single quotes. Characters are
stored as Unicode characters.
Escape |
Meaning |
\n \t \b \r \f \\ |
Newline Tab Backspace Carriage return Form feed Backslash |
- What is a String literals?
A string is a combination
of characters. string literals are a set of characters that are enclosed within
double quotes. As they are real objects, it is possible to concatenate, modify
and test them. For example, “This is a test string” represents a string.
Strings can contain character constants and Unicode characters.
- What are token in Java?
Token means, the smallest individual units
of program. In Java the following token are available.
White space
Identifiers
Literals
Comments
Separators
Keywords
- What is a variable? How to declare
variable in java?
The variable is the basic
unit of storage in a java program. A variable is defined by the combination of
an identifier, a type, and an optional initialize. All variables must be
declared before they can be used. The basic form of a variable declaration is
shown have
Type identifier [= value],[,identifier [=value]]
The
type in one of java’s atomic types. The identifier is the name of the variable.
For example
int a,b,c;
int d=3,c=5;
- What is a variable? What are the
different types of variables?
Variable
are locations in the memory that can hold values. Java has three kinds of
variable namely,
- Instance variable
- Local variable
- Class variable
Local variables are used
inside blocks as counts or in methods as temporary variables. Once the block or
the method is executed, the variable ceases to exist. Instance variable are
used to define attributes or the state of a particular object. These are used
to store information needed by multiple methods in the objects.
- Write a note on integer data types
in Java.
Integers are used for
storing integer values. There are four kinds of integer types in Java. Each of
these can hold a different range of values. The values can either be positive
or negative
Type |
Size |
byte short int long |
8 bits 16 bits 32 bits 64 bits |
- Write a note on float data types
in Java.
Float is used to store
numbers with decimal part. There are two floating point data types in Java
namely, the float and the double
Type |
Size |
float double |
32 bits 64 bits |
- What are the difference between
static variable and instance variable?
The data or variables,
defined within a class are called instance variables.
Instance variables
declared as static are, essentially, global variables. When objects of its
class are declared, no copy of a static variable is made.
- Define Array? How to declare an
array?
An array is an object
that stores a list of items. Each slot in an array holds individual elements.
An array should be of a single type, comprising of integers, strings and so on.
To create an array, a variable to hold the array is declared, and a new object
is created and assigned to it.
- Write a note on conditional
operator in Java.
The conditional operator
is otherwise known as the ternary operator and is considered to be an
alternative to the if else construct. It returns a value and the syntax is:
<test> ? <pass> : <fail>
Where,<test> is the condition to be tested. If the condition returns true
then the statement given in <pass> will be executed. Otherwise, the
statement given in <fail> will be executed.
- List out the operator in Java
§ Arithmetic Operators
§ Increment and Decrement Operators
§ Bitewise Operators
§ Relational Operators
§ Logical Operators
§ Assignment Operators
- What are jump statements in Java?
In java have three jump
statements
§ return
§ continue
§ break
- Differentiable between break and
continue statements?
The break keyword halts
the execution of the current loop and forces control out of the loop. The term
break refers to the act of breaking out of a b lock of code. Continue is
similar to break, except that instead of halting the execution of the loop, it
starts the next iteration.
- What is means by Garbage
Collection?
In certain languages like
C++, dynamically allocated objects must be manually released by use of a delete
operator. In Java deallocation happens automatically. The technique that
accomplishes this is called garbage collection.
- Write any three OOP principal?
§ Encapsulation
§ Inheritance
§ Polymorphism
- What is a class? Give an example?
A
class defines the shape and behavior of an object and is a template for
multiple objects with similar features.
(OR)
A class is a new data type. Once defined, this new type can be used to create
objects of that type. Thus, a class is a template for an object, and an object
is an instance of a class
- Distinguish between a class and an
object?
A class is a template for
an object, and an object is an instance of a class
- Define abstract class?
Abstract classes are
classes from which instances are usually not created. It is basically used to
contain common characteristics of its derived classes. Abstract classes are
generally higher up the hierarchy and act as super classes. Methods can also be
declared as abstract. This implies that non-abstract classes must implement
these methods
- Define Inner Class ?
An inner class is a
nested class whose instance exists within an instance of its enclosing class
and has direct access to the instance members of its enclosing instance
- What are classes in Java?
- What is meant by an innerclass?
An inner class is a nested class whose
instance exists within an instance of its enclosing class and has direct access
to the instance members of its enclosing instance
class <EnclosingClass>
{
class <InnerClass>
{
}
}
- What are constructors?
A constructor initializes an object
immediately upon creation. It has the same name as the class in which it
resides and is syntactically similar to a method. Once defined, the constructor
is automatically called immediately after the object is created, before
the new operator completes.
- Define method overloading?
In Java it is possible to define two or
more methods within the same class that share the same name, as long as their
parameter declarations are different. When this is the case, the methods are
said to be overload, and the process is referred to as method
overloading.
- Define method?
Methods are functions that operates on
instances of classes in which they are defined. Objects can communicate with
each other using methods and can call methods in other classes. Just as there
are class and instance variable, there are class and instance methods. Instance
methods apply and operate on an instance of the class while class methods
operate on the class.
- What are the uses of the keyword
‘final’?
§ The class can be declared as final, if
instances or subclasses are not to be created.
§ The variables are declared as final, value
of the variable must be provided at the time of declaration.
§ The Method can be declared as final
indicating that they cannot be overridden by subclasses.
- What are static methods?
Static methods and
variables can be used independently of any object. To do so, you need only
specify the name of their class following by the dot operator.
- What is inheritance?
In
Object-Oriented programming, inheritance refers to the properties of a class
being available to many other classes. A derived class / sub class is one that
has been created from an existing class. Inheritance is the process of deriving
a class from a super class or a base class. No changes are made to the base
class. The derived class has a larger set of properties that its base class.
Inheritance has two advantages
a) Reusability of code
b) Data and methods of a super class are physically available to its subclasses
- What is a package?
Packages
contain a set of classes in order to ensure that class names are unique.
Packages are containers for classes that are used to compartmentalize the class
name space. Packages are stored in a hierarchical manner and are explicitly
imported into new class definition. A period is used as separator to enable
this.
- Write a note on import statement?
Classes external to a
program be imported before they can be used. To import a class the import keyword
should be used as given below
import
<classname>
The classes in
Java are arranged in hierarchical order. The Java library consists of a number
of package. These package contain a set of related classes. The whole path of
the class must be specified to import a class from the Java library, For
instance, to import the Data class from the util package use
the following code.
import
java.util.Date;
It is also possible to
import all classes that belong to a package using the * symbol.
- Define interface?
An interface is a collection of abstract
behavior that individual classes can implement. It is defined like a class. An
interface consists of a set of method definition. Any class implementing it
should provide code for all its methods
- Define an exception
An
exception is an abnormal condition, which occurs during the execution of a
program Exceptions are erroneous events like division by zero, opening of a
file that does not exist, etc. A java execution is an object, which describes
the error condition that has materialized in the program.
- Explain the usage of try and catch
clause
The try and catch clause
is used to handle an exception explicitly. The advantages of using the try and
catch clause are that, it fixes the error and prevents the program from
terminating abruptly.
- What is use of ‘throw statement’
give an example? (or) state the purpose of the throw statement.
Whenever
a program does not want to handle exception using the try block, it can use the
throws clause. The throws clause is responsible to handle the different types
of exceptions generated by the program. This clause usually contains a list of
the various types of exception that are likely to occur in the program.
- List any three common run time
errors.
Exception |
Meaning |
ArithmeticException
ArrayIndexOutOfBoundsException
IllegalThreadStateException |
Arithmetic error, such as
divide-by-zero
Array index is out-of-bounds
Requested operation not compatible
with current thread state |
- Define deadlock?
This
occurs when two threads have a circular dependency on a pair of synchronized
objects. For example, suppose one thread enters the monitor on object X and
another thread enters the monitor on object Y. If the thread in X tries to call
any synchronized method on Y, it will block as expected. However, if the thread
in Y, in turn, tries to call any synchronized method on X, the thread waits
forever, because to access X, it would have to release its own lock on Y so
that the first thread could complete.
- Define multithreading?
A thread is a line of
execution. It is the smallest unit of code that is dispatched by the scheduler.
Thus, a process can contain multiple threads to execute its different sections.
This is called multithread.
- List out the advantages of
multithreading.
The advantages are as
follows
- Can be created faster
- Requires less overheads
- Inter-process communication is
faster
- Context switching is faster
- Maximum use of CPU time
- Define the term thread.
A thread is a line of
execution. It is the smallest unit of code that is dispatched by the scheduler.
Thus, a process can contain multiple threads to execute its different sections.
This is called multithread.
- List the several states of
‘Thread’ in Java.
There are four states
associated with a thread namely – new, runnable, dead, blocked
- What is synchronization? Briefly
explain.
Two or more threads
accessing the same data simultaneously may lead to loss of data integrity. For
example, when two people access a savings account, it is possible that one
person may overdraw and the cheque may bounce. The importance of updating of
the pass book can be well understood in this case.
- What is the use of ‘Super’
Keyword? Give an example.
Usage of ‘super’ keyword’
1. The first calls the
superclass constructor
2. To access a member of the
superclass that has been hidden by a member of a subclass
- What are applets?
An applet is a dynamic
and interactive program that runs inside a web page displayed by a Java capable
browser. This can also be executed using the appletviewer.
- What are Byte Stream in Java?
The byte stream classes
provide a rich environment for handling byte-oriented I/O.
List of Byte Stream
classes
§ ByteArrayInputStream
§ ByteArrayOutputStream
§ FilteredByteStreams
§ BufferedByteStreams
- What are Character Stream in Java?
The Character Stream
classes provide a rich environment for handling
character-
oriented I/O.
List of Character Stream
classes
§ FileReader
§ FileWriter
§ CharArrayReader
§ CharArrayWriter
- Write a note on char Array Reader
The CharArrayReader
allows the usage of a character array as an InputStream. The usage of
CharArrayReader class is similar to ByteArrayInputStream. The constructor is
given below:
public CharArrayReader(char c[ ])
- How will you find out the length
of a string in java? Give an example?
length( ) method is used
to number of characters is string. For example,
String str=”Hello”;
System.out.println(“Length
of string is “+str.length( ));
- Name any three tags used in Java
Doc Comment
Java
supports three types of comments. The first two are the // and the /*. The
third type is called a documentation comment. It begins with the character
sequence /**. It ends with*/.
In Java have javadoc tags
Tag
Meaning
@author
Identifies the author of a class
@deprecated
Specifies that a class or member is deprecated
@param
Documents a method’s parameter
@return
Documents a method’s return value
- What is an internet Address?
Every
computer connected to a network has a unique IP address. An IP address is a
32-bit number which has four numbers separated by periods. It is possible to
connect to the Internet either directly or by using Internet Service Provider.
By connecting directly to the Internet, the computer is assigned with a
permanent IP address. In case connection is made using ISP, it assigns a
temporary IP address for each session. A simple IP address is given
below
80.0.0.78
- Define the role of the type
modifiers transient and volatile?
When an instance variable
is declared as transient, then its value need not persist when an object is
stored.
The volatile modifier
tells the compiler that the variable modified by volatile can be changed
unexpectedly by other parts of your program.
- What are datagram?
Datagram
is a type of packet that represents an entire communication. There is no
necessity to have connection or disconnection stages when communicating using
datagram. This is less reliable than communication using TCP/IP.
- Define Proxy Server.
A
proxy server speaks the client side of a protocol to another server. This is
often required when clients have certain restrictions on which servers they can
connect to. Thus, a client would connect to a proxy server, which did not have
such restrictions, and the proxy server would in turn communicate for the
client. A proxy server has the additional ability to filter certain requests or
cache the results of those requests for future use.
- What is the use of URL class in
Java? Name any two methods in it.
URL stands for uniform
Resource Locator and it points to resource files on the Internet. The URL has
four components – the protocol, IP address or
the hostname, port number and actual file
path
Methods
getPort(
) à get
the port number
getHost( ) à get the host name specified in URL
getFile( ) à get the file name
- List the AWT controls?
§ Label
§ Button
§ Checkbox
§ TextComponent
§ Choice
§ List
§ Scrollbar
- Write a note on push Button
Control?
A push button is a
component that contains a label and that generates as event when it is pressed.
Push buttons are objects of type Button. Button defines these two constructors.
Button( )
Button( String str)
The first version creates
an empty button. The second creates a button that contains str as a label.
- Write a note on
Borderlayout?
The BorderLayout class
implements a common layout style for top-level windows. It has four narrow,
fixed-width components at the edges and one large area in the center. The four
sides are referred to as north, south, east, and west. The middles area is called
the center. Here are the constructors defined by BorderLayout
BorderLayout( )
BorderLayout(int horz, int vert)
- Write a note on check box control
in Java?
A check box is a control
that is used to turn an option on or off. It consists of a small box that can
either contain a check mark or not. There is a label associated with each check
box that describes what option the box represents. You change the state of a
check box by clicking on it. Check boxes can be used individually or as part of
a group. Check boxes are objects of the Checkbox class.
Checkbox( )
Checkbox( String str)
Checkbox( String str, Boolean on)
Checkbox( String str, Boolean on, CheckboxGroup cbGroup)
- Distinguish between component and
container
Component is an abstract
class that encapsulates all of the attributes of a visual component. All user
interface elements that are displayed on the screen and that interact with the
user are subclasses of Component.
The
container class is a subclass of Component. It has additional methods that
allow other Component objects to be nested within it. Other Container objects
can be stored inside of a container.
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