Java J2EE Faqs

8/11/2019 Java J2EE Faqs

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Edited By Mahendra Kumar Shrivas [[email protected]]- +919098759901

Java Platform Question

1. What is a platform?A platform is the hardware or software environment in which a program runs.

Most platforms can be described as a combination of the operating system and

hardware, like Windows 2000/XP, Linux, Solaris, and MacOS.

2. What is the main difference between Java platform and other platforms?The Java platform differs from most other platforms in that it\s a

software-only platform that runs on top of other hardware-based platforms.

The Java platform has two components:

a. The Java Virtual Machine (Java VM)

b. The Java Application Programming Interface (Java API)

3. What is the Java Virtual Machine?The Java Virtual Machine is a software that can be ported onto various

hardware-based platforms.

4. What is the Java API?The Java API is a large collection of ready-made software components that

provide many useful capabilities, such as graphical user interface (GUI)widgets.

5. What is the package?

The package is a Java namespace or part of Java libraries. The Java API isgrouped into libraries of related classes and interfaces; these libraries are

known as packages.

6. What is native code?The native code is code that after you compile it, the compiled code runs

on a specific hardware platform.

7. Is Java code slower than native code?

Not really. As a platform-independent environment, the Java platform can be

a bit slower than native code. However, smart compilers, well-tuned

interpreters, and just-in-time bytecode compilers can bring performance close

to that of native code without threatening portability.

Java Basic Question

8. What are the advantages of OOPL?Object oriented programming languages directly

represent the real life objects. The features of OOPL as inhreitance, polymorphism,

encapsulation makes it powerful.

9. What do mean by polymorphisum, inheritance, encapsulation?Ans: Polymorhisum:

is a feature of OOPl that at run time depending upon the type of object the appropriatemethod is called.

Inheritance: is a feature of OOPL that represents the "is a" relationship between different


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objects(classes). Say in real life a manager is a employee. So in OOPL manger class is

inherited from the employee class.Encapsulation: is a feature of OOPL that is used to hide the information.

10.

What do you mean by static methods?Ans: By using the static method there is no needcreating an object of that class to use that method. We can directly call that method on

that class. For example, say class A has static function f(), then we can call f() function as

A.f(). There is no need of creating an object of class A.

11.What do you mean by virtual methods?Ans: virtual methods are used to use the

polymorhism feature in C++. Say class A is inherited from class B. If we declare say

fuction f() as virtual in class B and override the same function in class A then at runtime

appropriate method of the class will be called depending upon the type of the object.

12.What are the disadvantages of using threads?

Ans: DeadLock.

13. Write the Java code to declare any constant (say gravitational constant) and to getits value Ans: Class ABC

{

static final float GRAVITATIONAL_CONSTANT = 9.8;public void getConstant()

{

System.out.println("Gravitational_Constant: " + GRAVITATIONAL_CONSTANT);

}

}

14.What do you mean by multiple inheritance in C++ ?Ans: Multiple inheritance is a

feature in C++ by which one class can be of different types. Say class teachingAssistantis inherited from two classes say teacher and Student.

15. Can you write Java code for declaration of multiple inheritance in Java ?

Ans: Class C extends A implements B{

}

16.What is a class?A class is a blueprint, or prototype, that defines the variables and the

methods common to all objects of a certain kind.

17.What is an object? An object is a software bundle of variables and related methods. an

instance of a class depicting the state and behavior at that particular time in real world.18.What is a method? Encapsulation of a functionality which can be called to perform

specific tasks.

19.What is encapsulation? Explain with an example.Encapsulation is the term given to

the process of hiding the implementation details of the object. Once an object isencapsulated, its implementation details are not immediately accessible any more. Instead

they are packaged and are only indirectly accessible via the interface of the object


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20.What is inheritance? Explain with an example.Inheritance in object oriented

programming means that a class of objects can inherit properties and methods fromanother class of objects.

21.

What is polymorphism? Explain with an example. In object-oriented programming,polymorphism refers to a programming languages ability to process objects differently

depending on their data type or class. More specifically, it is the ability to redefine

methods for derived classes. For example, given a base class shape, polymorphism

enables the programmer to define different area methods for any number of derived

classes, such as circles, rectangles and triangles. No matter what shape an object is,

applying the area method to it will return the correct results. Polymorphism is considered

to be a requirement of any true object-oriented programming language

22.Is multiple inheritance allowed in Java? No, multiple inheritance is not allowed inJava.

23.What is interpreter and compiler? Java interpreter converts the high level language

code into a intermediate form in Java called as bytecode, and then executes it, where as acompiler converts the high level language code to machine language making it very

hardware specific24.What is JVM?The Java interpreter along with the runtime environment required to run

the Java application in called as Java virtual machine(JVM)

25.What are the different types of modifiers? There are access modifiers and there are

other identifiers. Access modifiers are public, protected and private. Other are final andstatic.

26.What are the access modifiers in Java? There are 3 access modifiers. Public, protected

and private, and the default one if no identifier is specified is called friendly, but

programmer cannot specify the friendly identifier explicitly.

27.

What is a wrapper class?They are classes that wrap a primitive data type so it can beused as a object

28.What is a static variable and static method? Whats the difference between two?The

modifier static can be used with a variable and method. When declared as static variable,there is only one variable no matter how instances are created, this variable is initialized

when the class is loaded. Static method do not need a class to be instantiated to be called,

also a non static method cannot be called from static method.29.What is garbage collection?Garbage Collection is a thread that runs to reclaim the

memory by destroying the objects that cannot be referenced anymore.

30.What is abstract class?Abstract class is a class that needs to be extended and its

methods implemented, class has to be declared abstract if it has one or more abstract

methods.31.

What is meant by final class, methods and variables? This modifier can be applied to

class method and variable. When declared as final class the class cannot be extended.

When declared as final variable, its value cannot be changed if is primitive value, if it is a

reference to the object it will always refer to the same object, internal attributes of the

object can be changed.

32.What is interface?Interface is a contact that can be implemented by a class; it has

method that needs implementation.


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46.What are the three types of priority?MAX_PRIORITY which is 10, MIN_PRIORITY

which is 1, NORM_PRIORITY which is 5.47.What is the use of synchronizations?Every object has a lock, when a synchronized

keyword is used on a piece of code the, lock must be obtained by the thread first toexecute that code, other threads will not be allowed to execute that piece of code till this

lock is released.

48.What are synchronized methods and synchronized statements?Synchronized

methods are methods that are used to control access to an object. For example, a thread

only executes a synchronized method after it has acquired the lock for the methods

object or class. Synchronized statements are similar to synchronized methods. A

synchronized statement can only be executed after a thread has acquired the lock for the

object or class referenced in the synchronized statement.49.

What are different ways in which a thread can enter the waiting state?A thread can

enter the waiting state by invoking its sleep() method, blocking on I/O, unsuccessfully

attempting to acquire an objects lock, or invoking an objects wait() method. It can alsoenter the waiting state by invoking its (deprecated) suspend() method.

50.Can a lock be acquired on a class?Yes, a lock can be acquired on a class. This lock isacquired on the classs Class object.

51.Whats new with the stop(), suspend() and resume() methods in new JDK 1.2?The

stop(), suspend() and resume() methods have been deprecated in JDK 1.2.

52.What is the preferred size of a component?The preferred size of a component is theminimum component size that will allow the component to display normally.

53.What method is used to specify a containers layout?The setLayout() method is used

to specify a containers layout. For example, setLayout(new FlowLayout()); will be set

the layout as FlowLayout.

54.

Which containers use a FlowLayout as their default layout?The Panel and Appletclasses use the FlowLayout as their default layout.

55.What state does a thread enter when it terminates its processing?When a thread

terminates its processing, it enters the dead state.56.

What is the Collections API?The Collections API is a set of classes and interfaces that

support operations on collections of objects. One example of class in Collections API is

Vector and Set and List are examples of interfaces in Collections API.57.What is the List interface?The List interface provides support for ordered collections

of objects. It may or may not allow duplicate elements but the elements must be ordered.

58.How does Java handle integer overflows and underflows?It uses those low order

bytes of the result that can fit into the size of the type allowed by the operation.

59.

What is the Vector class?The Vector class provides the capability to implement agrowable array of objects. The main visible advantage of this class is programmer

neednt to worry about the number of elements in the Vector.

60.What modifiers may be used with an inner class that is a member of an outer class?A (non-local) inner class may be declared as public, protected, private, static, final, or

abstract.

61.If a method is declared as protected, where may the method be accessed?A

protected method may only be accessed by classes or interfaces of the same package or

by subclasses of the class in which it is declared.


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62.What is an Iterator interface?The Iterator interface is used to step through the

elements of a Collection.

63.How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8characters?Unicode requires 16 bits, ASCII require 7 bits (although the ASCIIcharacter set uses only 7 bits, it is usually represented as 8 bits), UTF-8 represents

characters using 8, 16, and 18 bit patterns, UTF-16 uses 16-bit and larger bit patterns

64.What is the difference between yielding and sleeping?Yielding means a thread

returning to a ready state either from waiting, running or after creation, where as sleeping

refers a thread going to a waiting state from running state. With reference to Java, when a

task invokes its yield() method, it returns to the ready state and when a task invokes its

sleep() method, it returns to the waiting state

65.What are wrapper classes?Wrapper classes are classes that allow primitive types to beaccessed as objects. For example, Integer, Double. These classes contain many methods

which can be used to manipulate basic data types

66.

Does garbage collection guarantee that a program will not run out of memory?No,it doesnt. It is possible for programs to use up memory resources faster than they are

garbage collected. It is also possible for programs to create objects that are not subject togarbage collection. The main purpose of Garbage Collector is recover the memory from

the objects which are no longer required when more memory is needed.

67.Name Component subclasses that support painting?The following classes support

painting: Canvas, Frame, Panel, and Applet.68.

What is a native method?A native method is a method that is implemented in a

language other than Java. For example, one method may be written in C and can be called

in Java.

69.How can you write a loop indefinitely?

for(;;) //for loop

while(true); //always true

70.Can an anonymous class be declared as implementing an interface and extending aclass?An anonymous class may implement an interface or extend a superclass, but maynot be declared to do both.

71.What is the purpose of finalization?The purpose of finalization is to give an

unreachable object the opportunity to perform any cleanup processing before the object is

garbage collected. For example, closing a opened file, closing a opened databaseConnection.

72.

What invokes a threads run() method?After a thread is started, via its start() methodor that of the Thread class, the JVM invokes the threads run() method when the thread is

initially executed.

73.What is the GregorianCalendar class?The GregorianCalendar provides support for

traditional Western calendars.

74.What is the SimpleTimeZone class?The SimpleTimeZone class provides support for a

Gregorian calendar.


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75.What is the Properties class?The properties class is a subclass of Hashtable that can be

read from or written to a stream. It also provides the capability to specify a set of defaultvalues to be used.

76.

What is the purpose of the Runtime class?The purpose of the Runtime class is toprovide access to the Java runtime system.

77.What is the purpose of the System class?The purpose of the System class is to provide

access to system resources.

78.What is the purpose of the finally clause of a try-catch-finally statement?The finally

clause is used to provide the capability to execute code no matter whether or not an

exception is thrown or caught. For example,

try

{

//some statements

}catch

{// statements when exception is cought

}finally{

//statements executed whether exception occurs or not

}

79.What is the Locale class?The Locale class is used to tailor program output to the

conventions of a particular geographic, political, or cultural region.80.

What must a class do to implement an interface?It must provide all of the methods in

the interface and identify the interface in its implements clause.

81.What is the serialization?The serialization is a kind of mechanism that makes a class or a beanpersistence by having its properties or fields and state information saved and

restored to and from storage.

82.How to make a class or a bean serializable?

By implementing either the java.io.Serializable interface, or thejava.io.Externalizable interface. As long as one class in a class\s

inheritance hierarchy implements Serializable or Externalizable, that class is

serializable.

83.How many methods in the Serializable interface?There is no method in the Serializable interface. The Serializable

interface acts as a marker, telling the object serialization tools that your

class is serializable.


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84.How many methods in the Externalizable interface?There are two methods in the Externalizable interface. You have toimplement these two methods in order to make your class externalizable. These

two methods are readExternal() and writeExternal().85.

What is the difference between Serializalble and Externalizable interface? When you

use Serializable interface, your class is serialized automatically

by default. But you can override writeObject() and readObject() two methods to

control more complex object serailization process. When you use Externalizable

interface, you have a complete control over your class\s serialization

process.

86.What is a transient variable?A transient variable is a variable that may not be serialized. If you don\twant some field not to be serialized, you can mark that field transient or

static.

87.

Which containers use a border layout as their default layout?The window, Frame and Dialog classes use a border layout as their default

layout.

88.How are Observer and Observable used?Objects that subclass the Observable class maintain a list of observers.

When an Observable object is updated it invokes the update() method of each of

its observers to notify the observers that it has changed state. The Observerinterface is implemented by objects that observe Observable objects.

89.What is synchronization and why is it important?With respect to multithreading, synchronization is the capability to

control the access of multiple threads to shared resources. Without

synchronization, it is possible for one thread to modify a shared object whileanother thread is in the process of using or updating that object\s value.

This often causes dirty data and leads to significant errors.

90.Is Java a super set of JavaScript?No. They are completely different. Some syntax may be similar.

91.What is user defined exception?Ans: There are many exception defined by java which are used to track the run timeexceptions and act accordingly. User can also define his exceptions that can be thrown in

the same way java exceptions.

92.What do you know about the garbage collector?Ans: Garbage collector is used to recollect memory from the us=nused objects. They are

the objects that are no longer needed because of function or class scope is going to finish.93.

What gives Java its write once and run anywhere nature?- Java is compiled to be a

byte code which is the intermediate language between source code and machine code.

This byte code is not platform specific and hence can be fed to any platform. After being

fed to the JVM, which is specific to a particular operating system, the code platform

specific machine code is generated thus making java platform independent.

94.What are the four pillar of OOP?- Abstraction, Encapsulation, Polymorphism and

Inheritance.


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95.Difference between a Class and an Object?- A class is a definition or prototype

whereas an object is an instance or living representation of the prototype.96.What is the difference between method overriding and overloading?- Overriding is a

method with the same name and arguments as in a parent, whereas overloading is thesame method name but different arguments.

97.What is a stateless protocol?- Without getting into lengthy debates, it is generally

accepted that protocols like HTTP are stateless i.e. there is no retention of state between a

transaction which is a single request response combination.

98.What is constructor chaining and how is it achieved in Java?- A child object

constructor always first needs to construct its parent (which in turn calls its parent

constructor.). In Java it is done via an implicit call to the no-args constructor as the first

statement.99.

What is passed by ref and what by value?- All Java method arguments are passed by

value. However, Java does manipulate objects by reference, and all object variables

themselves are references100. Can RMI and Corba based applications interact?- Yes they can. RMI is

available with IIOP as the transport protocol instead of JRMP.

101. You can create a String object as String str = abc"; Why cant a buttonobject be created as Button bt = abc";? Explain- The main reason you cannot create

a button by Button bt1= abc"; is because abc is a literal string (something slightly

different than a String object, by the way) and bt1 is a Button object. The only object inJava that can be assigned a literal String is java.lang.String. Important to note that you are

NOT calling a java.lang.String constuctor when you type String s = abc";

102. What does the abstract keyword mean in front of a method? A class?-

Abstract keyword declares either a method or a class. If a method has a abstract keyword

in front of it,it is called abstract method.Abstract method hs no body.It has onlyarguments and return type.Abstract methods act as placeholder methods that are

implemented in the subclasses. Abstract classes cant be instantiated.If a class is declared

as abstract,no objects of that class can be created.If a class contains any abstract methodit must be declared as abstract.

103. How many methods do u implement if implement the Serializable Interface?- The Serializable interface is just a marker interface, with no methods of its own toimplement. Other marker interfaces are

java.rmi.Remote

java.util.EventListener

104. What are the practical benefits, if any, of importing a specific class ratherthan an entire package (e.g. import java.net.* versus import java.net.Socket)?- It

makes no difference in the generated class files since only the classes that are actuallyused are referenced by the generated class file. There is another practical benefit to

importing single classes, and this arises when two (or more) packages have classes with

the same name. Take java.util.Timer and javax.swing.Timer, for example. If I import

java.util.* and javax.swing.* and then try to use Timer", I get an error while compiling

(the class name is ambiguous between both packages). Lets say what you really wanted


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was the javax.swing.Timer class, and the only classes you plan on using in java.util are

Collection and HashMap. In this case, some people will prefer to importjava.util.Collection and import java.util.HashMap instead of importing java.util.*. This

will now allow them to use Timer, Collection, HashMap, and other javax.swing classeswithout using fully qualified class names in.

105. What is the difference between logical data independence and physical data

independence?- Logical Data Independence - meaning immunity of external schemas to

changed in conceptual schema. Physical Data Independence - meaning immunity of

conceptual schema to changes in the internal schema.

106. What is a user-defined exception?- Apart from the exceptions already defined

in Java package libraries, user can define his own exception classes by extending

Exception class.107.

Describe the visitor design pattern?- Represents an operation to be performed

on the elements of an object structure. Visitor lets you define a new operation without

changing the classes of the elements on which it operates. The root of a class hierarchydefines an abstract method to accept a visitor. Subclasses implement this method with

visitor.visit(this). The Visitor interface has visit methods for all subclasses of thebaseclass in the hierarchy.

108. What is the Collections API?- The Collections API is a set of classes and

interfaces that support operations on collections of objects

109. What is the List interface?- The List interface provides support for orderedcollections of objects.

110. What is the Vector class?- The Vector class provides the capability to

implement a growable array of objects

111. What is an Iterator interface?- The Iterator interface is used to step through the

elements of a Collection112. Which java.util classes and interfaces support event handling?- The

EventObject class and the EventListener interface support event processing

113. What is the GregorianCalendar class?- The GregorianCalendar providessupport for traditional Western calendars

114. What is the Locale class?- The Locale class is used to tailor program output to

the conventions of a particular geographic, political, or cultural region115. What is the SimpleTimeZone class?- The SimpleTimeZone class provides

support for a Gregorian calendar

116. What is the Map interface?- The Map interface replaces the JDK 1.1 Dictionary

class and is used associate keys with values

117.

What is the highest-level event class of the event-delegation model?- Thejava.util.EventObject class is the highest-level class in the event-delegation class

hierarchy

118. What is the Collection interface?- The Collection interface provides support for

the implementation of a mathematical bag - an unordered collection of objects that may

contain duplicates

119. What is the Set interface?- The Set interface provides methods for accessing the

elements of a finite mathematical set. Sets do not allow duplicate elements


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134. What method must be implemented by all threads?- All tasks must implement

the run() method, whether they are a subclass of Thread or implement the Runnableinterface.

135.

What are the two basic ways in which classes that can be run as threads may

be defined?- A thread class may be declared as a subclass of Thread, or it may

implement the Runnable interface.

Java AWT Questions

1.

What is meant by Controls and what are different types of controls?- Controls arecomponenets that allow a user to interact with your application. The AWT supports the

following types of controls:

o Labels

o Push buttonso Check boxeso

Choice listso

Lists

o

Scroll bars

o

Text components

These controls are subclasses of Component.

2. Which method of the component class is used to set the position and the size of a

component?- setBounds(). The following code snippet explains this:3. txtName.setBounds(x,y,width,height);

places upper left corner of the text field txtName at point (x,y) with the width and heightof the text field set as width and height.

4. Which TextComponent method is used to set a TextComponent to the read-onlystate?- setEditable()

5. How can the Checkbox class be used to create a radio button?- By associating

Checkbox objects with a CheckboxGroup.

6. What methods are used to get and set the text label displayed by a Button object?-getLabel( ) and setLabel( )

7. What is the difference between a Choice and a List?- Choice: A Choice is displayed

in a compact form that requires you to pull it down to see the list of available choices.

Only one item may be selected from a Choice. List: A List may be displayed in such a

way that several List items are visible. A List supports the selection of one or more List

items.


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o FlowLayout: The elements of a FlowLayout are organized in a top to bottom, left

to right fashion.o BorderLayout: The elements of a BorderLayout are organized at the borders

(North, South, East and West) and the center of a container.o

CardLayout: The elements of a CardLayout are stacked, one on top of the other,

like a deck of cards.

o

GridLayout: The elements of a GridLayout are of equal size and are laid out using

the square of a grid.

o GridBagLayout:

The elements of a GridBagLayout are organized according to a grid.However, the

elements are of different sizes and may occupy more

than one row or column of the grid. In addition, the rows and columns may havedifferent sizes.

The default Layout Manager of Panel and Panel sub classes is FlowLayout.

15.Can I add the same component to more than one container?- No. Adding a

component to a container automatically removes it from any previous parent (container).

16.How can we create a borderless window?- Create an instance of the Window class,give it a size, and show it on the screen.

17. Frame aFrame = new Frame();

18.

Window aWindow = new Window(aFrame);

19.

aWindow.setLayout(new FlowLayout());

20. aWindow.add(new Button("Press Me"));

21.

aWindow.getBounds(50,50,200,200);

22.

aWindow.show();

23.

Can I create a non-resizable windows? If so, how?- Yes. By using setResizable()method in class Frame.

24.Which containers use a BorderLayout as their default layout? Which containers usea FlowLayout as their default layout?- The Window, Frame and Dialog classes use a

BorderLayout as their default layout. The Panel and the Applet classes use the

FlowLayout as their default layout.

25.How do you change the current layout manager for a container?

o Use the setLayout method

o

Once created you cannot change the current layout manager of a component

o

Use the setLayoutManager methodo

Use the updateLayout method

Answer: a.

26.What is the difference between a MenuItem and a CheckboxMenuItem?- The

CheckboxMenuItem class extends the MenuItem class to support a menu item that may

be checked or unchecked.

Java GUI Question


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1. What advantage do Javas layout managers provide over traditional windowingsystems?- Java uses layout managers to lay out components in a consistent manneracross all windowing platforms. Since Javas layout managers arent tied to absolute

sizing and positioning, they are able to accomodate platform-specific differences amongwindowing systems.

2. What is the difference between the paint() and repaint() methods?- The paint()

method supports painting via a Graphics object. The repaint() method is used to cause

paint() to be invoked by the AWT painting thread.

3. How can the Checkbox class be used to create a radio button?- By associating

Checkbox objects with a CheckboxGroup

4. What is the difference between a Choice and a List?- A Choice is displayed in a

compact form that requires you to pull it down to see the list of available choices. Onlyone item may be selected from a Choice. A List may be displayed in such a way that

several List items are visible. A List supports the selection of one or more List items.

5.

What interface is extended by AWT event listeners?- All AWT event listeners extendthe java.util.EventListener interface.

6. What is a layout manager?- A layout manager is an object that is used to organizecomponents in a container

7. Which Component subclass is used for drawing and painting?- Canvas

8. What are the problems faced by Java programmers who dont use layout managers?

- Without layout managers, Java programmers are faced with determining how their GUIwill be displayed across multiple windowing systems and finding a common sizing and

positioning that will work within the constraints imposed by each windowing system

9. What is the difference between a Scrollbar and a ScrollPane? (Swing) - A Scrollbar

is a Component, but not a Container. A ScrollPane is a Container. A ScrollPane

handles its own events and performs its own scrolling.

Java Applet Questions

1. What is an Applet? Should applets have constructors?- Applets are small programs transferred through Internet, automatically installed and run

as part of web-browser. Applets implements functionality of a client. Applet is a dynamicand interactive program that runs inside a Web page displayed by a Java-capable

browser. We dont have the concept of Constructors in Applets. Applets can be invoked

either through browser or through Appletviewer utility provided by JDK.

2. What are the Applets Life Cycle methods? Explain them?- Following are methodsin the life cycle of an Applet:

o

init() method - called when an applet is first loaded. This method is called only

once in the entire cycle of an applet. This method usually intialize the variables to

be used in the applet.

o start( ) method - called each time an applet is started.


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o paint() method - called when the applet is minimized or refreshed. This method is

used for drawing different strings, figures, and images on the applet window.o stop( ) method - called when the browser moves off the applets page.o

destroy( ) method - called when the browser is finished with the applet.3.

What is the sequence for calling the methods by AWT for applets?- When an applet

begins, the AWT calls the following methods, in this sequence:

o

init()

o

start()

o paint()

When an applet is terminated, the following sequence of method calls takes place :

o

stop()

o

destroy()

4. How do Applets differ from Applications?- Following are the main differences:

Application: Stand Alone, doesnt need

web-browser. Applet: Needs no explicit installation on local machine. Can be transferred

through Internet on to the local machine and may run as part of web-browser.

Application: Execution starts with main() method. Doesnt work if main is not there.Applet: Execution starts with init() method. Application: May or may not be a GUI.

Applet: Must run within a GUI (Using AWT). This is essential feature of applets.5.

Can we pass parameters to an applet from HTML page to an applet? How?- We

can pass parameters to an applet using tag in the following way:o

o

Access those parameters inside the applet is done by calling getParameter() method

inside the applet. Note that getParameter() method returns String value corresponding tothe parameter name.

6. How do we read number information from my applets parameters, given that

Applets getParameter() method returns a string?- Use the parseInt() method in the Integer Class, the Float(String) constructor or

parseFloat() method in the Class Float, or theDouble(String) constructor or parseDoulbl() method in the class Double.

7. How can I arrange for different applets on a web page to communicate with each

other?- Name your applets inside the Applet tag and invoke AppletContexts getApplet()

method in your applet code to obtain references to the

other applets on the page.8. How do I select a URL from my Applet and send the browser to that page?- Ask the

applet for its applet context and invoke showDocument() on that context object.


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9.

URL targetURL;

10.

String URLString

11. AppletContext context = getAppletContext();

12.

try13.

{

14. targetURL = new URL(URLString);

15. }

16.

catch (MalformedURLException e)

17.

{

18. // Code for recover from the exception

19.

}

20.

context. showDocument (targetURL);

21.Can applets on different pages communicate with each other?- No, Not Directly. The applets will exchange the information at one meeting place either

on the local file system or at remote system.

22.How do I determine the width and height of my application?

- Use the getSize() method, which the Applet class inherits from the Component class inthe Java.awt package. The getSize() method returns the size of the applet as a Dimensionobject, from which you extract separate width, height fields. The following code snippet

explains this:23. Dimension dim = getSize();

24.

int appletwidth = dim.width();

25.

int appletheight = dim.height();

26.Which classes and interfaces does Applet class consist?- Applet class consists of a

single class, the Applet class and three interfaces: AppletContext, AppletStub, and

AudioClip.

27.What is AppletStub Interface?- The applet stub interface provides the means by which an applet and the browser

communicate. Your code will not typically implement this interface.

28.What tags are mandatory when creating HTML to display an applet?

1.

name, height, width

2.

code, name

3.

codebase, height, width

4. code, height, width

Correct answer is d.

29.What are the Applets information methods?- The following are the Applets information methods: getAppletInfo() method: Returns a

string describing the applet, its author, copyright information, etc. getParameterInfo( )

method: Returns an array of string describing the applets parameters.

30.What are the steps involved in Applet development?- Following are the steps

involved in Applet development:o

Create/Edit a Java source file. This file must contain a class which extends Applet

class.o

Compile your program using javac


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o Execute the appletviewer, specifying the name of your applets source file or html

file. In case the applet information is stored in html file then Applet can beinvoked using java enabled web browser.

31.

Which method is used to output a string to an applet? Which function is this method

included in?- drawString( ) method is used to output a string to an applet. This method

is included in the paint method of the Applet.

Java database interview questions

1. How do you call a Stored Procedure from JDBC? - The first step is to create a

CallableStatement object. As with Statement and PreparedStatement objects, this is done

with an open Connection object. A CallableStatement object contains a call to a stored

procedure.2.

CallableStatement cs =

3.

con.prepareCall("{call SHOW_SUPPLIERS}");4. ResultSet rs = cs.executeQuery();

5. Is the JDBC-ODBC Bridge multi-threaded? - No. The JDBC-ODBC Bridge does not

support concurrent access from different threads. The JDBC-ODBC Bridge uses

synchronized methods to serialize all of the calls that it makes to ODBC. Multi-threadedJava programs may use the Bridge, but they wont get the advantages of multi-threading.

6. Does the JDBC-ODBC Bridge support multiple concurrent open statements per

connection? - No. You can open only one Statement object per connection when you are

using the JDBC-ODBC Bridge.

7. What is cold backup, hot backup, warm backup recovery? - Cold backup (All these

files must be backed up at the same time, before the databaseis restarted). Hot backup

(official name is online backup) is a backup taken of each tablespace while the databaseis running and is being accessed by the users.

8. When we will Denormalize data? - Data denormalization is reverse procedure, carriedout purely for reasons of improving performance. It maybe efficient for a high-

throughput system to replicate data for certain data.

9. What is the advantage of using PreparedStatement? - If we are using

PreparedStatement the execution time will be less. The PreparedStatement object

contains not just an SQL statement, but the SQL statement that has been precompiled.

This means that when the PreparedStatement is executed,the RDBMS can just run the

PreparedStatements Sql statement without having to compile it first.10.What is a dirty read"? - Quite often in database processing, we come across the

situation wherein one transaction can change a value, and a second transaction can readthis value before the original change has been committed or rolled back. This is known as

a dirty read scenario because there is always the possibility that the first transaction may

rollback the change, resulting in the second transaction having read an invalid value.

While you can easily command a database to disallow dirty reads, this usually degrades

the performance of your application due to the increased locking overhead. Disallowing

dirty reads also leads to decreased system concurrency.

11.What is Metadata and why should I use it? - Metadata (data about data) isinformation about one of two things: Database information (java.sql.DatabaseMetaData),


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or Information about a specific ResultSet (java.sql.ResultSetMetaData). Use

DatabaseMetaData to find information about your database, such as its capabilities andstructure. Use ResultSetMetaData to find information about the results of an SQL query,

such as size and types of columns12.

Different types of Transaction Isolation Levels? - The isolation level describes the

degree to which the data being updated is visible to other transactions. This is important

when two transactions are trying to read the same row of a table. Imagine two

transactions: A and B. Here three types of inconsistencies can occur:

o Dirty-read: A has changed a row, but has not committed the changes. B reads the

uncommitted data but his view of the data may be wrong if A rolls back his

changes and updates his own changes to the database.o

Non-repeatable read: B performs a read, but A modifies or deletes that data later.If B reads the same row again, he will get different data.

o

Phantoms: A does a query on a set of rows to perform an operation. B modifies

the table such that a query of A would have given a different result. The table maybe inconsistent.

TRANSACTION_READ_UNCOMMITTED : DIRTY READS, NON-REPEATABLE

READ AND PHANTOMS CAN OCCUR.TRANSACTION_READ_COMMITTED : DIRTY READS ARE PREVENTED, NON-REPEATABLE READ AND PHANTOMS CAN OCCUR.

TRANSACTION_REPEATABLE_READ : DIRTY READS , NON-REPEATABLE

READ ARE PREVENTED AND PHANTOMS CAN OCCUR.

TRANSACTION_SERIALIZABLE : DIRTY READS, NON-REPEATABLE READ

AND PHANTOMS ARE PREVENTED.

13.What is 2 phase commit? - A 2-phase commit is an algorithm used to ensure the

integrity of a committing transaction. In Phase 1, the transaction coordinator contacts

potential participants in the transaction. The participants all agree to make the results of

the transaction permanent but do not do so immediately. The participants log information

to disk to ensure they can complete In phase 2 f all the participants agree to commit, thecoordinator logs that agreement and the outcome is decided. The recording of this

agreement in the log ends in Phase 2, the coordinator informs each participant of the

decision, and they permanently update their resources.

14.How do you handle your own transaction ? - Connection Object has a method calledsetAutocommit(Boolean istrue)

- Default is true. Set the Parameter to false , and begin your transaction15.

What is the normal procedure followed by a java client to access the db.? - The

database connection is created in 3 steps:

1. Find a proper database URL

2. Load the database driver

3. Ask the Java DriverManager class to open a connection to your database

In java code, the steps are realized in code as follows:


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4. Create a properly formatted JDBR URL for your database. (See FAQ on JDBC URL for

more information). A JDBC URL has the formjdbc:someSubProtocol://myDatabaseServer/theDatabaseName

5.

Class.forName("my.database.driver");6.

Connection conn = DriverManager.getConnection("a.JDBC.URL",

databaseLogin","databasePassword");

16.What is a data source? - A DataSource class brings another level of abstraction than

directly using a connection object. Data source can be referenced by JNDI. Data Source

may point to RDBMS, file System , any DBMS etc.

17.What are collection pools? What are the advantages? - A connection pool is a cache

of database connections that is maintained in memory, so that the connections may be

reused18.

How do you get Column names only for a table (SQL Server)? Write the Query. -19. select name from syscolumns

20.

where id=(select id from sysobjects wherename='user_hdr')

21. order by colid --user_hdr is the table name

J2EE - Servlet Questions

1. What is a servlet?

Servlets are modules that extend request/response-oriented servers,such as Java-enabledweb servers. For example, a servlet might be responsible for taking data in an HTMLorder-entry form and applying the business logic used to update a companys order

database. Servlets are to servers what applets are to browsers. Unlike applets, however,

servlets have no graphical user interface.

2. Whats the advantages using servlets over using CGI?Servlets provide a way to generate dynamic documents that is both easier to write and

faster to run. Servlets also address the problem of doing server-side programming withplatform-specific APIs: they are developed with the Java Servlet API, a standard Java

extension.

3. What are the general advantages and selling points of Servlets?

A servlet can handle multiple requests concurrently, and synchronize requests. Thisallows servlets to support systems such as online

real-time conferencing. Servlets can forward requests to other servers and servlets. Thus

servlets can be used to balance load among several servers that mirror the same content,and to partition a single logical service over several servers, according to task type or

organizational boundaries.4.

Which package provides interfaces and classes for writing servlets?javax

5. Whats the Servlet Interface?The central abstraction in the Servlet API is the Servlet interface. All servlets implement


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this interface, either directly or, more

commonly, by extending a class that implements it such as HttpServlet.Servlets >Generic Servlet > HttpServlet > MyServlet.

The Servlet interface declares, but does not implement, methods that manage the servletand its communications with clients. Servlet writers provide some or all of these methods

when developing a servlet.

6. When a servlet accepts a call from a client, it receives two objects. What are they?ServletRequest (which encapsulates the communication from the client to the server) and

ServletResponse (which encapsulates the communication from the servlet back to the

client). ServletRequest and ServletResponse are interfaces defined inside javax.servlet

package.

7. What information does ServletRequest allow access to?

Information such as the names of the parameters passed in by the client, the protocol

(scheme) being used by the client, and the names

of the remote host that made the request and the server that received it. Also the inputstream, as ServletInputStream.Servlets use the input stream to get data from clients that

use application protocols such as the HTTP POST and GET methods.

8. What type of constraints can ServletResponse interface set on the client?It can set the content length and MIME type of the reply. It also provides an output

stream, ServletOutputStream and a Writer through

which the servlet can send the reply data.

9. Explain servlet lifecycle?

Each servlet has the same life cycle: first, the server loads and initializes the servlet

(init()), then the servlet handles zero or more client requests (service()), after that the

server removes the servlet (destroy()). Worth noting that the last step on some servers is

done when they shut down.10.How does HTTP Servlet handle client requests?

An HTTP Servlet handles client requests through its service method. The service method

supports standard HTTP client requests by dispatching each request to a method designedto handle that request.

J2EE - JSP Questions

1. What is JSP? Describe its concept.JSP is a technology that combines HTML/XML

markup languages and elements of Java programming Language to return dynamic

content to the Web client, It is normally used to handle Presentation logic of a web

application, although it may have business logic.2. What are the lifecycle phases of a JSP?

JSP page looks like a HTML page but is a servlet. When presented with JSP page the JSP

engine does the following 7 phases.

1. Page translation: -page is parsed, and a java file which is a servlet is created.2.

Page compilation: page is compiled into a class file

3.

Page loading : This class file is loaded.

4.

Create an instance :- Instance of servlet is created


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5. jspInit() method is called

6. _jspService is called to handle service calls7. _jspDestroy is called to destroy it when the servlet is not required.

3.

What is a translation unit?JSP page can include the contents of other HTML pages orother JSP files. This is done by using the include directive. When the JSP engine is

presented with such a JSP page it is converted to one servlet class and this is called a

translation unit, Things to remember in a translation unit is that page directives affect the

whole unit, one variable declaration cannot occur in the same unit more than once, the

standard action jsp:useBean cannot declare the same bean twice in one unit.

4. How is JSP used in the MVC model?JSP is usually used for presentation in the MVC

pattern (Model View Controller ) i.e. it plays the role of the view. The controller deals

with calling the model and the business classes which in turn get the data, this data is thenpresented to the JSP for rendering on to the client.

5. What are context initialization parameters?Context initialization parameters are

specified by the in the web.xml file, these are initialization parameterfor the whole application and not specific to any servlet or JSP.

6. What is a output comment?A comment that is sent to the client in the viewable pagesource. The JSP engine handles an output comment as un-interpreted HTML text,

returning the comment in the HTML output sent to the client. You can see the comment

by viewing the page source from your Web browser.

7. What is a Hidden Comment?A comment that documents the JSP page but is not sent tothe client. The JSP engine ignores a hidden comment, and does not process any code

within hidden comment tags. A hidden comment is not sent to the client, either in the

displayed JSP page or the HTML page source. The hidden comment is useful when you

want to hide or comment out part of your JSP page.

8.

What is a Expression?Expressions are act as place holders for language expression,expression is evaluated each time the page is accessed.

9. What is a Declaration?It declares one or more variables or methods for use later in the

JSP source file. A declaration must contain at least one complete declarative statement.You can declare any number of variables or methods within one declaration tag, as long

as semicolons separate them. The declaration must be valid in the scripting language used

in the JSP file.10.What is a Scriptlet?A scriptlet can contain any number of language statements, variable

or method declarations, or expressions that are valid in the page scripting language.

Within scriptlet tags, you can declare variables or methods to use later in the file, write

expressions valid in the page scripting language, use any of the JSP implicit objects or

any object declared with a .11.

What are the implicit objects? List them.Certain objects that are available for the use

in JSP documents without being declared first. These objects are parsed by the JSP

engine and inserted into the generated servlet. The implicit objects are:

o

request

o response

o pageContext

o sessiono

application


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o out

o configo pageo

exception12.

Whats the difference between forward and sendRedirect?When you invoke a

forward request, the request is sent to another resource on the server, without the client

being informed that a different resource is going to process the request. This process

occurs completely within the web container And then returns to the calling method.

When a sendRedirect method is invoked, it causes the web container to return to the

browser indicating that a new URL should be requested. Because the browser issues a

completely new request any object that are stored as request attributes before the redirect

occurs will be lost. This extra round trip a redirect is slower than forward.13.

What are the different scope values for the ?The different scope

values for are:

o

pageo

request

o sessiono application

14.Why are JSP pages the preferred API for creating a web-based client program?Because no plug-ins or security policy files are needed on the client systems(applet does).

Also, JSP pages enable cleaner and more module application design because they providea way to separate applications programming from web page design. This means

personnel involved in web page design do not need to understand Java programming

language syntax to do their jobs.

15.Is JSP technology extensible?Yes, it is. JSP technology is extensible through the

development of custom actions, or tags, which are encapsulated in tag libraries.16.What is difference between custom JSP tags and beans?Custom JSP tag is a tag you

defined. You define how a tag, its attributes and its body are interpreted, and then group

your tags into collections called tag libraries that can be used in any number of JSP files.Custom tags and beans accomplish the same goals encapsulating complex behavior into

simple and accessible forms. There are several differences:

o

Custom tags can manipulate JSP content; beans cannot.o

Complex operations can be reduced to a significantly simpler form with custom

tags than with beans.

o Custom tags require quite a bit more work to set up than do beans.

o Custom tags usually define relatively self-contained behavior, whereas beans are

often defined in one servlet and used in a different servlet or JSP page.o

Custom tags are available only in JSP 1.1 and later, but beans can be used in all

JSP 1.x versions.

17.What is Struts?- A Web page development framework. Struts combines Java Servlets,Java Server Pages, custom tags, and message resources into a unified framework. It is a


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cooperative, synergistic platform, suitable for development teams, independent

developers, and everyone between.18.How is the MVC design pattern used in Struts framework?- In the MVC design

pattern, application flow is mediated by a central Controller. The Controller delegatesrequests to an appropriate handler. The handlers are tied to a Model, and each handler

acts as an adapter between the request and the Model. The Model represents, or

encapsulates, an applications business logic or state. Control is usually then forwarded

back through the Controller to the appropriate View. The forwarding can be determined

by consulting a set of mappings, usually loaded from a database or configuration file.

This provides a loose coupling between the View and Model, which can make an

application significantly easier to create and maintain. Controller: Servlet controller

which supplied by Struts itself; View: what you can see on the screen, a JSP page andpresentation components; Model: System state and a business logic JavaBeans.

J2EE Questions

1. What makes J2EE suitable for distributed multitier Applications?

- The J2EE platform uses a multitier distributed application model. Application logic is

divided into components according to function, and the various application components

that make up a J2EE application are installed on different machines depending on the tier

in the multitiered J2EE environment to which the application component belongs. The

J2EE application parts are:o

Client-tier components run on the client machine.o

Web-tier components run on the J2EE server.o

Business-tier components run on the J2EE server.

o

Enterprise information system (EIS)-tier software runs on the EIS server.2.

What is J2EE?- J2EE is an environment for developing and deploying enterprise

applications. The J2EE platform consists of a set of services, application programming

interfaces (APIs), and protocols that provide the functionality for developing multitiered,

web-based applications.

3. What are the components of J2EE application?- A J2EE component is a self-contained functional software unit that is assembled into a

J2EE application with its related classes and files and communicates with othercomponents. The J2EE specification defines the following J2EE components:

1.

Application clients and applets are client components.

2.

Java Servlet and JavaServer Pages technology components are web components.

3.

Enterprise JavaBeans components (enterprise beans) are business components.4. Resource adapter components provided by EIS and tool vendors.

4. What do Enterprise JavaBeans components contain?- Enterprise JavaBeans

components contains Business code, which is logic

that solves or meets the needs of a particular business domain such as banking, retail, orfinance, is handled by enterprise beans running in the business tier. All the business code

is contained inside an Enterprise Bean which receives data from client programs,

processes it (if necessary), and sends it to the enterprise information system tier for


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storage. An enterprise bean also retrieves data from storage, processes it (if necessary),

and sends it back to the client program.5. Is J2EE application only a web-based?- No, It depends on type of application that

client wants. A J2EE application can be web-based or non-web-based. if an applicationclient executes on the client machine, it is a non-web-based J2EE application. The J2EE

application can provide a way for users to handle tasks such as J2EE system or

application administration. It typically has a graphical user interface created from Swing

or AWT APIs, or a command-line interface. When user request, it can open an HTTP

connection to establish communication with a servlet running in the web tier.

6. Are JavaBeans J2EE components?- No. JavaBeans components are not considered

J2EE components by the J2EE specification. They are written to manage the data flow

between an application client or applet and components running on the J2EE server orbetween server components and a database. JavaBeans components written for the J2EE

platform have instance variables and get and set methods for accessing the data in the

instance variables. JavaBeans components used in this way are typically simple in designand implementation, but should conform to the naming and design conventions outlined

in the JavaBeans component architecture.7. Is HTML page a web component?- No. Static HTML pages and applets are bundled

with web components during application assembly, but are not considered web

components by the J2EE specification. Even the server-side utility classes are not

considered web components, either.8.

What can be considered as a web component?- J2EE Web components can be either

servlets or JSP pages. Servlets are Java programming language classes that dynamically

process requests and construct responses. JSP pages are text-based documents that

execute as servlets but allow a more natural approach to creating static content.

9.

What is the container?- Containers are the interface between a component and the low-level platform specific functionality that supports the component. Before a Web,

enterprise bean, or application client component can be executed, it must be assembled

into a J2EE application and deployed into its container.10.

What are container services?- A container is a runtime support of a system-level

entity. Containers provide components with services such as lifecycle management,

security, deployment, and threading.11.What is the web container?- Servlet and JSP containers are collectively referred to as

Web containers. It manages the execution of JSP page and servlet components for J2EE

applications. Web components and their container run on the J2EE server.

12.What is Enterprise JavaBeans (EJB) container?- It manages the execution of

enterprise beans for J2EE applications.Enterprise beans and their container run on the J2EE server.

13.What is Applet container?- IManages the execution of applets. Consists of a Web

browser and Java Plugin running on the client together.

14.How do we package J2EE components?- J2EE components are packaged separately

and bundled into a J2EE application for deployment. Each component, its related files

such as GIF and HTML files or server-side utility classes, and a deployment descriptor

are assembled into a module and added to the J2EE application. A J2EE application is

composed of one or more enterprise bean,Web, or application client component modules.


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The final enterprise solution can use one J2EE application or be made up of two or more

J2EE applications, depending on design requirements. A J2EE application and each of itsmodules has its own deployment descriptor. A deployment descriptor is an XML

document with an .xml extension that describes a components deployment settings.15.

What is a thin client?- A thin client is a lightweight interface to the application that

does not have such operations like query databases, execute complex business rules, or

connect to legacy applications.

16.What are types of J2EE clients?- Following are the types of J2EE clients:

o Applets

o Application clients

o Java Web Start-enabled rich clients, powered by Java Web Start technology.o

Wireless clients, based on Mobile Information Device Profile (MIDP) technology.17.

What is deployment descriptor?- A deployment descriptor is an Extensible Markup

Language (XML) text-based file with an .xml extension that describes a components

deployment settings. A J2EE application and each of its modules has its own deploymentdescriptor. For example, an enterprise bean module deployment descriptor declares

transaction attributes and security authorizationsfor an enterprise bean. Because deployment descriptor information is declarative, it can

be changed without modifying the bean source code. At run time, the J2EE server reads

the deployment descriptor and acts upon the component accordingly.

18.What is the EAR file?- An EAR file is a standard JAR file with an .ear extension,named from Enterprise ARchive file. A J2EE application with all of its modules is

delivered in EAR file.

19.What is JTA and JTS?- JTA is the abbreviation for the Java Transaction API. JTS is

the abbreviation for the Jave Transaction Service. JTA provides a standard interface and

allows you to demarcate transactions in a manner that is independent of the transactionmanager implementation. The J2EE SDK implements the transaction manager with JTS.

But your code doesnt call the JTS methods directly. Instead, it invokes the JTA methods,

which then call the lower-level JTS routines. Therefore, JTA is a high level transactioninterface that your application uses to control transaction. and JTS is a low level

transaction interface and ejb uses behind the scenes (client code doesnt directly interact

with JTS. It is based on object transaction service(OTS) which is part of CORBA.20.What is JAXP?- JAXP stands for Java API for XML. XML is a language for

representing and describing text-based data which can be read and handled by any

program or tool that uses XML APIs. It provides standard services to determine the type

of an arbitrary piece of data, encapsulate access to it, discover the operations available on

it, and create the appropriate JavaBeans component to perform those operations.21.

What is J2EE Connector?- The J2EE Connector API is used by J2EE tools vendors

and system integrators to create resource adapters that support access to enterprise

information systems that can be plugged into any J2EE product. Each type of database or

EIS has a different resource adapter. Note: A resource adapter is a software component

that allows J2EE application components to access and interact with the underlying

resource manager. Because a resource adapter is specific to its resource manager, there is

typically a different resource adapter for each type of database or enterprise information

system.


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22.What is JAAP?- The Java Authentication and Authorization Service (JAAS) provides a

way for a J2EE application to authenticate and authorize a specific user or group of usersto run it. It is a standard Pluggable Authentication Module (PAM) framework that

extends the Java 2 platform security architecture to support user-based authorization.23.

What is Java Naming and Directory Service?- The JNDI provides naming and

directory functionality. It provides applications with methods for performing standard

directory operations, such as associating attributes with objects and searching for objects

using their attributes. Using JNDI, a J2EE application can store and retrieve any type of

named Java object. Because JNDI is independent of any specific implementations,

applications can use JNDI to access multiple naming and directory services, including

existing naming and

directory services such as LDAP, NDS, DNS, and NIS.

References

http://www.oracle.comhttp://www.naukri.com

http://www.timesjob.comhttp://www.techinterviews.com

Thanks to Mr. Sachin Rastogi for his great contribution.

Documents

Java J2EE Faqs