young mind

A young man was getting ready to graduate college. For many months he had admired a beautiful sports car in a dealer's showroom, and knowing his father could well afford it, he told him that was all he wanted. 
As Graduation Day approached, the young man awaited signs that his father had purchased the car. Finally, on the morning  of his graduation his father called him into his private study. His father told him how proud he was to have such a fine son, and  told him how much he loved him. He handed his son a beautiful wrapped gift box. 
Curious, but somewhat disappointed the young man opened the box and found a lovely, leather-bound Bible. Angrily, he raised his voice at his father and said, "With all your money you give  me  a Bible?" and stormed out of the house, leaving the holy book. Many years passed and the young man was very successful in business. 
    

He had a beautiful home and wonderful family, but realized his father was very old, and thought perhaps he should go to him. He had not seen him since that graduation day. Before he could make arrangements, he received a telegram telling him his father had passed away, and willed all of his possessions to his son. He needed   to come home immediately and take care things. When he arrived at his father's house, sudden sadness and regret filled his heart. 
He began to search his father's important papers and saw the still new Bible, just as he had left it years ago. With tears, he opened the Bible and began to turn the pages. As he read those   words, a car key dropped from an envelope taped behind the Bible.

It  had a tag with the dealer's name, the same dealer who had the sports  car he had desired. On the tag was the date of his graduation

and the words...PAID IN FULL. 
How many times do we miss God's blessings because they are not packaged as we expected?

Question on oracle and sql

How to display ename, dname even if there no employees working in a
particular department(use outer join). (Oracle DB) (SQL)
Answer
Select ename, dname from emp e, dept d where e.deptno (+)=
d.deptno;

Question How to display employee name and his manager name. (Oracle DB) (SQL)
Answer Select e.ename, m.ename from emp e, emp m where e.mgr=m.empno;

Question
How to display the department name along with total salary in each
department. (Oracle DB) (SQL)
Answer Select deptno, sum(sal) from emp group by deptno;

Question How to display the department name and total number of employees in
each department. (Oracle DB) (SQL)
Answer select deptno,count(*) from emp group by deptno;

Question How to display the current date and time (Oracle DB) (SQL)
Answer select to_char(sysdate,'month mon dd yy yyyy hh:mi:ss') from dual;

Question How to delete the rows of employees who are working in the company for
more than 2 years. (Oracle DB) (SQL)
Answer delete from emp where floor(sysdate-hiredate)>2*365;

Question
How to provide a commission to employees who are not earning any
commission. (Oracle DB) (SQL)
Answer update emp set comm=300 where comm is null;

Question Write a query, If any employee has commission his commission should be
incremented by 10% of his salary. (Oracle DB) (SQL)
Answer update emp set comm=comm*10/100 where comm is not null;

Question
How to display employee name and department name for each employee.
(Oracle DB) (SQL)
Answer select ename,dname from emp e, dept d where e.deptno=d.deptno;

Question How to display employee number, name and location of the department
in which he is working. (Oracle DB) (SQL)
Answer Select empno, ename, loc from emp e, dept d where e.deptno=d.deptno;

Question
I want to give a validation saying that sal cannot be greater 10,000(note
give a name to this column). How to do this? (Oracle DB) (SQL)
Answer alter table emp add constraint emp_sal_check check (sal<10000);

Question
How to add column called as mgr to your emp table. This column should
be related to empno. Give a
command to add this constraint (Oracle DB) (SQL)
Answer
Alter table emp add mgr number (5);
Alter table emp add constraint emp_mgr foreign key (empno);

Question
How to add dept no column to your emp table. This dept no column
should be related to deptno column of
dept table (Oracle DB) (SQL)
Answer
Alter table emp add deptno number (3);
Alter table emp1 add constraint emp1_deptno foreign key(deptno)
references dept(deptno);

Question
How to create table called as new emp. Using single command create this
table as well as to get data
into this table (use create table as) (Oracle DB) (SQL)
Answer create table newemp as select *from emp;

Question How to create table called as newemp. This table should contain only
empno,ename, dname (Oracle DB) (SQL)
Answer create table newemp as select empno,ename,dname from emp e , dept d
where e.deptno=d.deptno;

Question How to create table emp with only one column empno (Oracle DB) (SQL)
Answer Create table emp (empno number(5));

Question How to add this column to emp table ename Varchar(20). (Oracle
DB) (SQL)
Answer alter table emp add ename varchar2(20) not null;

Question
How to add primary key constraint after the table has been created?
(Oracle DB) (SQL)
Answer alter table emp add constraint emp_empno primary key (empno);

Question How to increase the length of ename column to 30 characters. (Oracle
DB) (SQL)
Answer alter table emp modify ename varchar2(30);

Question How to add salary column to emp table. (Oracle DB) (SQL)
Answer alter table emp add sal number(7,2);

java

1. What is the difference between procedural and object-oriented programs?-l

 a) In procedural program, programming logic follows certain procedures and the instructions are executed one after another. In OOP program, unit of program is object, which is nothing but combination of data and code. b) In procedural program, data is exposed to the whole program whereas in OOPs program, it is accessible with in the object and which in turn assures the security of the code.

Ø      What are Encapsulation, Inheritance and Polymorphism?-

Encapsulation is the mechanism that binds together code and data it manipulates and keeps both safe from outside interference and misuse. Inheritance is the process by which one object acquires the properties of another object. Polymorphism is the feature that allows one interface to be used for general class actions.

Ø      What is the difference between Assignment and Initialization?-

Assignment can be done as many times as desired whereas initialization can be done only once.

Ø      What is OOPs?-

Object oriented programming organizes a program around its data, i. e. , objects and a set of well-defined interfaces to that data. An object-oriented program can be characterized as data controlling access to code.

Ø      What are Class, Constructor and Primitive data types?-

Class is a template for multiple objects with similar features and it is a blue print for objects. It defines a type of object according to the data the object can hold and the operations the object can perform. Constructor is a special kind of method that determines how an object is initialized when created. Primitive data types are 8 types and they are: byte, short, int, long, float, double, boolean, char.

Ø      What is an Object and how do you allocate memory to it?-

Object is an instance of a class and it is a software unit that combines a structured set of data with a set of operations for inspecting and manipulating that data. When an object is created using new operator, memory is allocated to it.

Ø      What is the difference between constructor and method?-

Constructor will be automatically invoked when an object is created whereas method has to be called explicitly.

Ø      What are methods and how are they defined?-

Methods are functions that operate on instances of classes in which they are defined. Objects can communicate with each other using methods and can call methods in other classes. Method definition has four parts. They are name of the method, type of object or primitive type the method returns, a list of parameters and the body of the method. A method’s signature is a combination of the first three parts mentioned above.

Ø      What is the use of bin and lib in JDK?-

Bin contains all tools such as javac, appletviewer, awt tool, etc., whereas lib contains API and all packages.

Ø      What is casting?-

Casting is used to convert the value of one type to another.

Ø      How many ways can an argument be passed to a subroutine and explain them?-

An argument can be passed in two ways. They are passing by value and passing by reference. Passing by value: This method copies the value of an argument into the formal parameter of the subroutine. Passing by reference: In this method, a reference to an argument (not the value of the argument) is passed to the parameter.







Ø      What is the difference between an argument and a parameter?-

While defining method, variables passed in the method are called parameters. While using those methods, values passed to those variables are called arguments.

Ø      What are different types of access modifiers?-

public: Any thing declared as public can be accessed from anywhere. private: Any thing declared as private can’t be seen outside of its class. protected: Any thing declared as protected can be accessed by classes in the same package and subclasses in the other packages. default modifier : Can be accessed only to classes in the same package.

Ø      What is final, finalize() and finally?-

final : final keyword can be used for class, method and variables. A final class cannot be subclassed and it prevents other programmers from subclassing a secure class to invoke insecure methods. A final method can’t be overridden. A final variable can’t change from its initialized value. finalize() : finalize() method is used just before an object is destroyed and can be called just prior to garbage collection. finally : finally, a key word used in exception handling, creates a block of code that will be executed after a try/catch block has completed and before the code following the try/catch block. The finally block will execute whether or not an exception is thrown. For example, if a method opens a file upon exit, then you will not want the code that closes the file to be bypassed by the exception-handling mechanism. This finally keyword is designed to address this contingency.

Ø      What is UNICODE?-

Unicode is used for internal representation of characters and strings and it uses 16 bits to represent each other.





Ø      What is Garbage Collection and how to call it explicitly?-

When an object is no longer referred to by any variable, java automatically reclaims memory used by that object. This is known as garbage collection. System. gc() method may be used to call it explicitly.

Ø      What is finalize() method?-

finalize () method is used just before an object is destroyed and can be called just prior to garbage collection.

Ø      What are Transient and Volatile Modifiers?-

Transient: The transient modifier applies to variables only and it is not stored as part of its object’s Persistent state. Transient variables are not serialized. Volatile: Volatile modifier applies to variables only and it tells the compiler that the variable modified by volatile can be changed unexpectedly by other parts of the program.

Ø      What is method overloading & method overriding?-

Method overloading: When a method in a class having the same method name with different arguments is said to be method overloading. Method overriding : When a method in a class having the same method name with same arguments is said to be method overriding.

Ø      What is diff. between overloading & overriding?-

a)    In overloading, there is a relationship between methods available in the same class whereas in overriding, there is relationship between a superclass method and subclass method. b) Overloading does not block inheritance from the superclass whereas overriding blocks inheritance from the superclass. c) In overloading, separate methods share the same name whereas in overriding, subclass method replaces the superclass. d) Overloading must have different method signatures whereas overriding must have same signature.







Ø      What is meant by Inheritance and what are its advantages?-

Inheritance is the process of inheriting all the features from a class. The advantages of inheritance are reusability of code and accessibility of variables and methods of the super class by subclasses.

Ø      What is the difference between this() and super()?-

this() can be used to invoke a constructor of the same class whereas super() can be used to invoke a super class constructor.



Ø      What is the difference between superclass and subclass?-

A super class is a class that is inherited whereas sub class is a class that does the inheriting.

Ø      What modifiers may be used with top-level class?-

public, abstract and final can be used for top-level class.

Ø      What are inner class and anonymous class?-

Inner class : classes defined in other classes, including those defined in methods are called inner classes. An inner class can have any accessibility including private. Anonymous class : Anonymous class is a class defined inside a method without a name and is instantiated and declared in the same place and cannot have explicit constructors.

Ø      What is a package?-

A package is a collection of classes and interfaces that provides a high-level layer of access protection and name space management.

Ø      What is a reflection package?-

java. lang. reflect package has the ability to analyze itself in runtime.





Ø      What is interface and its use?-

Interface is similar to a class which may contain method’s signature only but not bodies and it is a formal set of method and constant declarations that must be defined by the class that implements it. Interfaces are useful for: a)Declaring methods that one or more classes are expected to implement b)Capturing similarities between unrelated classes without forcing a class relationship. c)Determining an object’s programming interface without revealing the actual body of the class.

Ø      What is an abstract class?-

An abstract class is a class designed with implementation gaps for subclasses to fill in and is deliberately incomplete.

Ø      What is the difference between Integer and int?-

a) Integer is a class defined in the java. lang package, whereas int is a primitive data type defined in the Java language itself. Java does not automatically convert from one to the other. b) Integer can be used as an argument for a method that requires an object, whereas int can be used for calculations.

Ø      What is a cloneable interface and how many methods does it contain?-

It is not having any method because it is a TAGGED or MARKER interface.

Ø      What is the difference between abstract class and interface?-

a)    All the methods declared inside an interface are abstract whereas abstract class must have at least one abstract method and others may be concrete or abstract. b) In abstract class, key word abstract must be used for the methods whereas interface we need not use that keyword for the methods. c) Abstract class must have subclasses whereas interface can’t have subclasses.







Ø      Can you have an inner class inside a method and what variables can you access?-

Yes, we can have an inner class inside a method and final variables can be accessed.

Ø      What is the difference between String and String Buffer?-

a) String objects are constants and immutable whereas StringBuffer objects are not. b) String class supports constant strings whereas StringBuffer class supports growable and modifiable strings.

Ø      What is the difference between Array and vector?-

Array is a set of related data type and static whereas vector is a growable array of objects and dynamic.

Ø      What is the difference between exception and error?-

The exception class defines mild error conditions that your program encounters. Exceptions can occur when trying to open the file, which does not exist, the network connection is disrupted, operands being manipulated are out of prescribed ranges, the class file you are interested in loading is missing. The error class defines serious error conditions that you should not attempt to recover from. In most cases it is advisable to let the program terminate when such an error is encountered.

Ø      What is the difference between process and thread?-

Process is a program in execution whereas thread is a separate path of execution in a program.

Ø      What is multithreading and what are the methods for inter-thread communication and what is the class in which these methods are defined?-

Multithreading is the mechanism in which more than one thread run independent of each other within the process. wait (), notify () and notifyAll() methods can be used for inter-thread communication and these methods are in Object class. wait() : When a thread executes a call to wait() method, it surrenders the object lock and enters into a waiting state. notify() or notifyAll() : To remove a thread from the waiting state, some other thread must make a call to notify() or notifyAll() method on the same object.

Ø      What is the class and interface in java to create thread and which is the most advantageous method?-

Thread class and Runnable interface can be used to create threads and using Runnable interface is the most advantageous method to create threads because we need not extend thread class here.

Ø      What are the states associated in the thread?-

Thread contains ready, running, waiting and dead states.

Ø      What is synchronization?-

Synchronization is the mechanism that ensures that only one thread is accessed the resources at a time.

Ø      When you will synchronize a piece of your code?-

When you expect your code will be accessed by different threads and these threads may change a particular data causing data corruption.

Ø      What is deadlock?-

When two threads are waiting each other and can’t precede the program is said to be deadlock.

Ø      What is daemon thread and which method is used to create the daemon thread?-

Daemon thread is a low priority thread which runs intermittently in the back ground doing the garbage collection operation for the java runtime system. setDaemon method is used to create a daemon thread.

Ø      Are there any global variables in Java, which can be accessed by other part of your program?-

No, it is not the main method in which you define variables. Global variables is not possible because concept of encapsulation is eliminated here.

Ø      What is an applet?-

Applet is a dynamic and interactive program that runs inside a web page displayed by a java capable browser.

Ø      What is the difference between applications and applets?-

a)Application must be run on local machine whereas applet needs no explicit installation on local machine. b)Application must be run explicitly within a java-compatible virtual machine whereas applet loads and runs itself automatically in a java-enabled browser. d)Application starts execution with its main method whereas applet starts execution with its init method. e)Application can run with or without graphical user interface whereas applet must run within a graphical user interface.

Ø      How does applet recognize the height and width?-

Using getParameters() method.

Ø      When do you use codebase in applet?-

When the applet class file is not in the same directory, codebase is used.

Ø      What is the lifecycle of an applet?-

init() method - Can be called when an applet is first loaded start() method - Can be called each time an applet is started. paint() method - Can be called when the applet is minimized or maximized. stop() method - Can be used when the browser moves off the applet’s page. destroy() method - Can be called when the browser is finished with the applet.

Ø      How do you set security in applets?-

using setSecurityManager() method

Ø      What is an event and what are the models available for event handling?-

An event is an event object that describes a state of change in a source. In other words, event occurs when an action is generated, like pressing button, clicking mouse, selecting a list, etc. There are two types of models for handling events and they are: a) event-inheritance model and b) event-delegation model

Ø      What are the advantages of the model over the event-inheritance model?-

The event-delegation model has two advantages over the event-inheritance model. They are: a)It enables event handling by objects other than the ones that generate the events. This allows a clean separation between a component’s design and its use. b)It performs much better in applications where many events are generated. This performance improvement is due to the fact that the event-delegation model does not have to be repeatedly process unhandled events as is the case of the event-inheritance.

Ø      What is source and listener?-

source : A source is an object that generates an event. This occurs when the internal state of that object changes in some way. listener : A listener is an object that is notified when an event occurs. It has two major requirements. First, it must have been registered with one or more sources to receive notifications about specific types of events. Second, it must implement methods to receive and process these notifications.

Ø      What is adapter class?-

An adapter class provides an empty implementation of all methods in an event listener interface. Adapter classes are useful when you want to receive and process only some of the events that are handled by a particular event listener interface. You can define a new class to act listener by extending one of the adapter classes and implementing only those events in which you are interested. For example, the MouseMotionAdapter class has two methods, mouseDragged()and mouseMoved(). The signatures of these empty are exactly as defined in the MouseMotionListener interface. If you are interested in only mouse drag events, then you could simply extend MouseMotionAdapter and implement mouseDragged() .

Ø      What is meant by controls and what are different types of controls in AWT?-

Controls are components that allow a user to interact with your application and the AWT supports the following types of controls: Labels, Push Buttons, Check Boxes, Choice Lists, Lists, Scrollbars, Text Components. These controls are subclasses of Component.

Ø      What is the difference between choice and list?-

A Choice is displayed in a compact form that requires you to pull it down to see the list of available choices and only one item may be selected from a choice. A List may be displayed in such a way that several list items are visible and it supports the selection of one or more list items.

Ø      What is the difference between scrollbar and scrollpane?-

A Scrollbar is a Component, but not a Container whereas Scrollpane is a Conatiner and handles its own events and perform its own scrolling.

Ø      What is a layout manager and what are different types of layout managers available in java AWT?-

A layout manager is an object that is used to organize components in a container. The different layouts are available are FlowLayout, BorderLayout, CardLayout, GridLayout and GridBagLayout.

Ø      How are the elements of different layouts organized?-

FlowLayout: The elements of a FlowLayout are organized in a top to bottom, left to right fashion. BorderLayout: The elements of a BorderLayout are organized at the borders (North, South, East and West) and the center of a container. CardLayout: The elements of a CardLayout are stacked, on top of the other, like a deck of cards. GridLayout: The elements of a GridLayout are of equal size and are laid out using the square of a grid. GridBagLayout: The elements of a GridBagLayout are organized according to a grid. However, the elements are of different size and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.

Ø      Which containers use a Border layout as their default layout?-

Window, Frame and Dialog classes use a BorderLayout as their layout.



Ø      Which containers use a Flow layout as their default layout?-

Panel and Applet classes use the FlowLayout as their default layout.

Ø      What are wrapper classes?-

Wrapper classes are classes that allow primitive types to be accessed as objects.

Ø      What are Vector, Hashtable, LinkedList and Enumeration?-

Vector : The Vector class provides the capability to implement a growable array of objects. Hashtable : The Hashtable class implements a Hashtable data structure. A Hashtable indexes and stores objects in a dictionary using hash codes as the object’s keys. Hash codes are integer values that identify objects. LinkedList: Removing or inserting elements in the middle of an array can be done using LinkedList. A LinkedList stores each object in a separate link whereas an array stores object references in consecutive locations. Enumeration: An object that implements the Enumeration interface generates a series of elements, one at a time. It has two methods, namely hasMoreElements() and nextElement(). HasMoreElemnts() tests if this enumeration has more elements and nextElement method returns successive elements of the series.

Ø      What is the difference between set and list?-

Set stores elements in an unordered way but does not contain duplicate elements, whereas list stores elements in an ordered way but may contain duplicate elements.

Ø      What is a stream and what are the types of Streams and classes of the Streams?-

A Stream is an abstraction that either produces or consumes information. There are two types of Streams and they are: Byte Streams: Provide a convenient means for handling input and output of bytes. Character Streams: Provide a convenient means for handling input & output of characters. Byte Streams classes: Are defined by using two abstract classes, namely InputStream and OutputStream. Character Streams classes: Are defined by using two abstract classes, namely Reader and Writer.

Ø      What is the difference between Reader/Writer and InputStream/Output Stream?-

The Reader/Writer class is character-oriented and the InputStream/OutputStream class is byte-oriented.

Ø      What is an I/O filter?-

An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.

Ø      What is serialization and deserialization?-

Serialization is the process of writing the state of an object to a byte stream. Deserialization is the process of restoring these objects.

Ø      What is JDBC?-

JDBC is a set of Java API for executing SQL statements. This API consists of a set of classes and interfaces to enable programs to write pure Java Database applications.

Ø      What are drivers available?-

a) JDBC-ODBC Bridge driver b) Native API Partly-Java driver c) JDBC-Net Pure Java driver d) Native-Protocol Pure Java driver

Ø      What is the difference between JDBC and ODBC?-

a)    OBDC is for Microsoft and JDBC is for Java applications. b) ODBC can’t be directly used with Java because it uses a C interface. c) ODBC makes use of pointers which have been removed totally from Java. d) ODBC mixes simple and advanced features together and has complex options for simple queries. But JDBC is designed to keep things simple while allowing advanced capabilities when required. e) ODBC requires manual installation of the ODBC driver manager and driver on all client machines. JDBC drivers are written in Java and JDBC code is automatically installable, secure, and portable on all platforms. f) JDBC API is a natural Java interface and is built on ODBC. JDBC retains some of the basic features of ODBC.



Ø      What are the types of JDBC Driver Models and explain them?-

There are two types of JDBC Driver Models and they are: a) Two tier model and b) Three tier model Two tier model: In this model, Java applications interact directly with the database. A JDBC driver is required to communicate with the particular database management system that is being accessed. SQL statements are sent to the database and the results are given to user. This model is referred to as client/server configuration where user is the client and the machine that has the database is called as the server. Three tier model: A middle tier is introduced in this model. The functions of this model are: a) Collection of SQL statements from the client and handing it over to the database, b) Receiving results from database to the client and c) Maintaining control over accessing and updating of the above.

Ø      What are the steps involved for making a connection with a database or how do you connect to a database?

a) Loading the driver : To load the driver, Class. forName() method is used. Class. forName(”sun. jdbc. odbc. JdbcOdbcDriver”); When the driver is loaded, it registers itself with the java. sql. DriverManager class as an available database driver. b) Making a connection with database: To open a connection to a given database, DriverManager. getConnection() method is used. Connection con = DriverManager. getConnection (”jdbc:odbc:somedb”, “user”, “password”); c) Executing SQL statements : To execute a SQL query, java. sql. statements class is used. createStatement() method of Connection to obtain a new Statement object. Statement stmt = con. createStatement(); A query that returns data can be executed using the executeQuery() method of Statement. This method executes the statement and returns a java. sql. ResultSet that encapsulates the retrieved data: ResultSet rs = stmt. executeQuery(”SELECT * FROM some table”); d) Process the results : ResultSet returns one row at a time. Next()
 method of ResultSet object can be called to move to the next row. The getString() and getObject() methods are used for retrieving column values: while(rs. next()) { String event = rs. getString(”event”); Object count = (Integer) rs. getObject(”count”);

Ø      What type of driver did you use in project?-

JDBC-ODBC Bridge driver (is a driver that uses native(C language) libraries and makes calls to an existing ODBC driver to access a database engine).

Ø      What are the types of statements in JDBC?-

Statement: to be used createStatement() method for executing single SQL statement PreparedStatement — To be used preparedStatement() method for executing same SQL statement over and over. CallableStatement — To be used prepareCall() method for multiple SQL statements over and over.

Ø      What is stored procedure?-

Stored procedure is a group of SQL statements that forms a logical unit and performs a particular task. Stored Procedures are used to encapsulate a set of operations or queries to execute on database. Stored procedures can be compiled and executed with different parameters and results and may have any combination of input/output parameters.

Ø      How to create and call stored procedures?-

To create stored procedures: Create procedure procedurename (specify in, out and in out parameters) BEGIN Any multiple SQL statement; END; To call stored procedures: CallableStatement csmt = con. prepareCall(”{call procedure name(?,?)}”); csmt. registerOutParameter(column no. , data type); csmt. setInt(column no. , column name) csmt. execute();

Ø      What is servlet?-

Servlets are modules that extend request/response-oriented servers, such as java-enabled web servers. For example, a servlet might be responsible for taking data in an HTML order-entry form and applying the business logic used to update a company’s order database.

Ø      What are the classes and interfaces for servlets?-

There are two packages in servlets and they are javax. servlet and

Ø      What is the difference between an applet and a servlet?-

a)    Servlets are to servers what applets are to browsers. b) Applets must have graphical user interfaces whereas servlets have no graphical user interfaces.



Ø      What is the difference between doPost and doGet methods?-

a)    doGet() method is used to get information, while doPost() method is used for posting information. b) doGet() requests can’t send large amount of information and is limited to 240-255 characters. However, doPost()requests passes all of its data, of unlimited length. c) A doGet() request is appended to the request URL in a query string and this allows the exchange is visible to the client, whereas a doPost() request passes directly over the socket connection as part of its HTTP request body and the exchange are invisible to the client.



Ø      What is the life cycle of a servlet?-

 Each Servlet has the same life cycle: a) A server loads and initializes the servlet by init () method. b) The servlet handles zero or more client’s requests through service() method. c) The server removes the servlet through destroy() method.

Ø      Who is loading the init() method of servlet?-  Web server



Ø      What are the different servers available for developing and deploying Servlets?-

a) Java Web Server b) JRun g) Apache Server h) Netscape Information Server i) Web Logic

Ø      How many ways can we track client and what are they?-

The servlet API provides two ways to track client state and they are: a) Using Session tracking and b) Using Cookies.

Ø      What is session tracking and how do you track a user session in servlets?-

Session tracking is a mechanism that servlets use to maintain state about a series requests from the same user across some period of time. The methods used for session tracking are: a) User Authentication - occurs when a web server restricts access to some of its resources to only those clients that log in using a recognized username and password. b) Hidden form fields - fields are added to an HTML form that are not displayed in the client’s browser. When the form containing the fields is submitted, the fields are sent back to the server. c) URL rewriting - every URL that the user clicks on is dynamically modified or rewritten to include extra information. The extra information can be in the form of extra path information, added parameters or some custom, server-specific URL change. d) Cookies - a bit of information that is sent by a web server to a browser and which can later be read back from that browser. e) HttpSession- places a limit on the number of sessions that can exist in
 memory. This limit is set in the session. maxresidents property.

Ø      What is Server-Side Includes (SSI)?-

Server-Side Includes allows embedding servlets within HTML pages using a special servlet tag. In many servlets that support servlets, a page can be processed by the server to include output from servlets at certain points inside the HTML page. This is accomplished using a special internal SSINCLUDE, which processes the servlet tags. SSINCLUDE servlet will be invoked whenever a file with an. shtml extension is requested. So HTML files that include server-side includes must be stored with an . shtml extension.

Ø      What are cookies and how will you use them?-

Cookies are a mechanism that a servlet uses to have a client hold a small amount of state-information associated with the user. a) Create a cookie with the Cookie constructor: public Cookie(String name, String value) b) A servlet can send a cookie to the client by passing a Cookie object to the addCookie() method of HttpServletResponse: public void HttpServletResponse. addCookie(Cookie cookie) c) A servlet retrieves cookies by calling the getCookies() method of HttpServletRequest: public Cookie[ ] HttpServletRequest. getCookie().

Ø      Is it possible to communicate from an applet to servlet and how many ways and how?-

Yes, there are three ways to communicate from an applet to servlet and they are: a) HTTP Communication(Text-based and object-based) b) Socket Communication c) RMI Communication



Ø      What is connection pooling?-

With servlets, opening a database connection is a major bottleneck because we are creating and tearing down a new connection for every page request and the time taken to create connection will be more. Creating a connection pool is an ideal approach for a complicated servlet. With a connection pool, we can duplicate only the resources we need to duplicate rather than the entire servlet. A connection pool can also intelligently manage the size of the pool and make sure each connection remains valid. A number of connection pool packages are currently available. Some like DbConnectionBroker are freely available from Java Exchange Works by creating an object that dispenses connections and connection Ids on request. The ConnectionPool class maintains a Hastable, using Connection objects as keys and Boolean values as stored values. The Boolean value indicates whether a connection is in use or not. A program calls getConnection() method of the ConnectionPool for getting Connection object it
 can use; it calls returnConnection() to give the connection back to the pool.

Ø      Why should we go for interservlet communication?-

Servlets running together in the same server communicate with each other in several ways. The three major reasons to use interservlet communication are: a) Direct servlet manipulation - allows to gain access to the other currently loaded servlets and perform certain tasks (through the ServletContext object) b) Servlet reuse - allows the servlet to reuse the public methods of another servlet. c) Servlet collaboration - requires to communicate with each other by sharing specific information (through method invocation)

Ø      Is it possible to call servlet with parameters in the URL?-

Yes. You can call a servlet with parameters in the syntax as (?Param1 = xxx || m2 = yyy).

Ø      What is Servlet chaining?-

Servlet chaining is a technique in which two or more servlets can cooperate in servicing a single request. In servlet chaining, one servlet’s output is piped to the next servlet’s input. This process continues until the last servlet is reached. Its output is then sent back to the client.



Ø      How do servlets handle multiple simultaneous requests?-

The server has multiple threads that are available to handle requests. When a request comes in, it is assigned to a thread, which calls a service method (for example: doGet(), doPost() and service()) of the servlet. For this reason, a single servlet object can have its service methods called by many threads at once.

Ø      What is the difference between TCP/IP and UDP?-

TCP/IP is a two-way communication between the client and the server and it is a reliable and there is a confirmation regarding reaching the message to the destination. It is like a phone call. UDP is a one-way communication only between the client and the server and it is not a reliable and there is no confirmation regarding reaching the message to the destination. It is like a postal mail.

Ø      What is Inet address?-

Every computer connected to a network has an IP address. An IP address is a number that uniquely identifies each computer on the Net. An IP address is a 32-bit number.

Ø      What is Domain Naming Service(DNS)?-

It is very difficult to remember a set of numbers(IP address) to connect to the Internet. The Domain Naming Service(DNS) is used to overcome this problem. It maps one particular IP address to a string of characters. For example, www. mascom. com implies com is the domain name reserved for US commercial sites, mascom is the name of the company and www is the name of the specific computer, which is mascom’s server.

Ø      What is URL?-

URL stands for Uniform Resource Locator and it points to resource files on the Internet. URL has four components: http://www. address. com:80/index.html, where http - protocol name, address - IP address or host name, 80 - port number and index.html - file path.





Ø      What is RMI and steps involved in developing an RMI object?-

Remote Method Invocation (RMI) allows java object that executes on one machine and to invoke the method of a Java object to execute on another machine. The steps involved in developing an RMI object are: a) Define the interfaces b) Implementing these interfaces c) Compile the interfaces and their implementations with the java compiler d) Compile the server implementation with RMI compiler e) Run the RMI registry f) Run the application

Ø      What is RMI architecture?-

RMI architecture consists of four layers and each layer performs specific functions: a) Application layer - contains the actual object definition. b) Proxy layer - consists of stub and skeleton. c) Remote Reference layer - gets the stream of bytes from the transport layer and sends it to the proxy layer. d) Transportation layer - responsible for handling the actual machine-to-machine communication.

Ø      what is UnicastRemoteObject?-

All remote objects must extend UnicastRemoteObject, which provides functionality that is needed to make objects available from remote machines.

Ø      Explain the methods, rebind() and lookup() in Naming class?-

rebind() of the Naming class(found in java. rmi) is used to update the RMI registry on the server machine. Naming. rebind(”AddSever”, AddServerImpl); lookup() of the Naming class accepts one argument, the rmi URL and returns a reference to an object of type AddServerImpl.

Ø      What is a Java Bean?-

A Java Bean is a software component that has been designed to be reusable in a variety of different environments.





Ø      What is a Jar file?-

Jar file allows to efficiently deploying a set of classes and their associated resources. The elements in a jar file are compressed, which makes downloading a Jar file much faster than separately downloading several uncompressed files. The package java. util. zip contains classes that read and write jar files.

Ø      What is BDK?-

BDK, Bean Development Kit is a tool that enables to create, configure and connect a set of set of Beans and it can be used to test Beans without writing a code.

Ø      What is JSP?-

JSP is a dynamic scripting capability for web pages that allows Java as well as a few special tags to be embedded into a web file (HTML/XML, etc). The suffix traditionally ends with .jsp to indicate to the web server that the file is a JSP files. JSP is a server side technology - you can’t do any client side validation with it. The advantages are: a) The JSP assists in making the HTML more functional. Servlets on the other hand allow outputting of HTML but it is a tedious process. b) It is easy to make a change and then let the JSP capability of the web server you are using deal with compiling it into a servlet and running it.

Ø      What are JSP scripting elements?-

JSP scripting elements lets to insert Java code into the servlet that will be generated from the current JSP page. There are three forms: a) Expressions of the form <%= expression %> that are evaluated and inserted into the output, b) Scriptlets of the formthat are inserted into the servlet’s service method, and c) Declarations of the form <%! Code %>that are inserted into the body of the servlet class, outside of any existing methods.

Ø      What are JSP Directives?-

A JSP directive affects the overall structure of the servlet class. It usually has the following form:<%@ directive attribute=”value” %> However, you can also combine multiple attribute settings for a single directive, as follows:<%@ directive attribute1=”value1&#8243; attribute 2=”value2&#8243; . . . attributeN =”valueN” %> There are two main types of directive: page, which lets to do things like import classes, customize the servlet superclass, and the like; and include, which lets to insert a file into the servlet class at the time the JSP file is translated into a servlet

Ø      What are Predefined variables or implicit objects?-

To simplify code in JSP expressions and scriptlets, we can use eight automatically defined variables, sometimes called implicit objects. They are request, response, out, session, application, config, pageContext, and page.

Ø      What are JSP ACTIONS?-

JSP actions use constructs in XML syntax to control the behavior of the servlet engine. You can dynamically insert a file, reuse JavaBeans components, forward the user to another page, or generate HTML for the Java plugin. Available actions include: jsp:include - Include a file at the time the page is requested. jsp:useBean - Find or instantiate a JavaBean. jsp:setProperty - Set the property of a JavaBean. jsp:getProperty - Insert the property of a JavaBean into the output. jsp:forward - Forward the requester to a newpage. Jsp: plugin - Generate browser-specific code that makes an OBJECT or EMBED

Ø      How do you pass data (including JavaBeans) to a JSP from a servlet?-

(1)            Request Lifetime: Using this technique to pass beans, a request dispatcher (using either “include” or forward”) can be called. This bean will disappear after processing this request has been completed. Servlet: request. setAttribute(”theBean”, myBean); RequestDispatcher rd = getServletContext(). getRequestDispatcher(”thepage. jsp”); rd. forward(request, response); JSP PAGE:<jsp: useBean id=”theBean” scope=”request” class=”. . . . . ” />

(2)            Session Lifetime: Using this technique to pass beans that are relevant to a particular session (such as in individual user login) over a number of requests. This bean will disappear when the session is invalidated or it times out, or when you remove it. Servlet: HttpSession session = request. getSession(true); session. putValue(”theBean”, myBean); /* You can do a request dispatcher here, or just let the bean be visible on the next request */ JSP Page:<jsp:useBean id=”theBean” scope=”session” class=”. . . ” />

(3)             Application Lifetime: Using this technique to pass beans that are relevant to all servlets and JSP pages in a particular app, for all users. For example, I use this to make a JDBC connection pool object available to the various servlets and JSP pages in my apps. This bean will disappear when the servlet engine is shut down, or when you remove it. Servlet: GetServletContext(). setAttribute(”theBean”, myBean); JSP PAGE:<jsp:useBean id=”theBean” scope=”application” class=”. . . ” />



Ø      How can I set a cookie in JSP?-

response. setHeader(”Set-Cookie”, “cookie string”); To give the response-object to a bean, write a method setResponse (HttpServletResponse response) - to the bean, and in jsp-file:<% bean. setResponse (response); %>

Ø      How can I delete a cookie with JSP?-

Say that I have a cookie called “foo, ” that I set a while ago & I want it to go away. I simply: <% Cookie killCookie = new Cookie(”foo”, null); KillCookie. setPath(”/”); killCookie. setMaxAge(0); response. addCookie(killCookie); %>

Ø      How are Servlets and JSP Pages related?-

JSP pages are focused around HTML (or XML) with Java codes and JSP tags inside them. When a web server that has JSP support is asked for a JSP page, it checks to see if it has already compiled the page into a servlet. Thus, JSP pages become servlets and are transformed into pure Java and then compiled, loaded into the server and executed.

So you think you are ready for the IT industry.Then try answering these questions

1.      What are the basic functions of an operating system?

2.      Explain briefly about, processor, assembler, compiler, loader, linker and the functions executed by them.

3.      What are the difference phases of software development? Explain briefly?

4.      Differentiate between RAM and ROM?

5.      What is DRAM? In which form does it store data?

6.      What is cache memory?

7.      What is hard disk and what is its purpose?

8.      Differentiate between Complier and Interpreter?

9.      What are the different tasks of Lexical analysis?

10.  What are the different functions of Syntax phase, Sheduler?

11.  What are the main difference between Micro-Controller and Micro- Processor?

12.  Describe different job scheduling in operating systems.

13.  What is a Real-Time System ?

14.  What is the difference between Hard and Soft real-time systems ?

15.  What is a mission critical system ?

16.  What is the important aspect of a real-time system ?

17.   If two processes which shares same system memory and system clock in a distributed system, What is it called?

18.  What is the state of the processor, when a process is waiting for some event to occur?

19.  What do you mean by deadlock?

20.  Explain the difference between microkernel and macro kernel.

21.  Give an example of microkernel.

22.  When would you choose bottom up methodology?

23.  When would you choose top down methodology?

24.  Write a small dc shell script to find number of FF in the design.

25.  Why paging is used ?

26.  Which is the best page replacement algorithm and Why? How much time is spent usually in each phases and why?

27.  Difference between Primary storage and secondary storage?

28.  What is multi tasking, multi programming, multi threading?

29.  Difference between multi threading and multi tasking?

30.  What is software life cycle?

31.  Demand paging, page faults, replacement algorithms, thrashing, etc.

32.  Explain about paged segmentation and segment paging

33.  While running DOS on a PC, which command would be used to duplicate the entire diskette?

j2ee

1.    What makes J2EE suitable for distributed multitiered Applications?
- The J2EE platform uses a multitiered 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:

§                  Client-tier components run on the client machine.

§                  Web-tier components run on the J2EE server.

§                  Business-tier components run on the J2EE server.

§                  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 other components. The J2EE specification defines the following J2EE components:

A.  Application clients and applets are client components.

B.   Java Servlet and JavaServer Pages technology components are web components.

C.   Enterprise JavaBeans components (enterprise beans) are business components.

D.   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, or finance, 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 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 application client 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 or between 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 design and 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. 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 its modules has its own deployment descriptor. A deployment descriptor is an XML document with an .xml extension that describes a component’s 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:

§                  Applets

§                  Application clients

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

§                  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 component’s deployment settings. A J2EE application and each of its modules has its own deployment descriptor. For example, an enterprise bean module deployment descriptor declares transaction attributes and security authorizations
for 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 transaction manager implementation. The J2EE SDK implements the transaction manager with JTS. But your code doesn’t 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 transaction interface that your application uses to control transaction. and JTS is a low level transaction interface and ejb uses behind the scenes (client code doesn’t 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.

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 users to 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.

24. 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 cooperative, synergistic platform, suitable for development teams, independent developers, and everyone between.

25. 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 delegates requests 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 application’s 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 and presentation components; Model: System state and a business logic JavaBeans.

Question: What is J2EE?
Answer: J2EE Stands for Java 2 Enterprise Edition. J2EE is an environment for developing and deploying enterprise applications. J2EE specification is defined by Sun Microsystems Inc. The J2EE platform is one of the best platform for the development and deployment of enterprise applications. The J2EE platform is consists of a set of services, application programming interfaces (APIs), and protocols, which provides the functionality necessary for developing multi-tiered, web-based applications. You can download the J2EE SDK and development tools from http://java.sun.com/.

Question: What do you understand by a J2EE module?
Answer: A J2EE module is a software unit that consists of one or more J2EE components of the same container type along with one deployment descriptor of that type. J2EE specification defines four types of modules:
a) EJB
b) Web
c) application client and
d) resource adapter
  
In the J2EE applications modules can be deployed as stand-alone units. Modules can also be assembled into J2EE applications.
   

Question: Tell me something about J2EE component?
Answer: J2EE component is a self-contained functional software unit supported by a container and configurable at deployment time. The J2EE specification defines the following J2EE components:

• Application clients and applets are components that run on the client.
• Java servlet and JavaServer Pages (JSP) technology components are Web components that run on the server.
• Enterprise JavaBeans (EJB) components (enterprise beans) are business components that run on the server. J2EE components are written in the Java programming language and are compiled in the same way as any program in the language. The difference between J2EE components and "standard" Java classes is that J2EE components are assembled into a J2EE application, verified to be well formed and in compliance with the J2EE specification, and deployed to production, where they are run and managed by the J2EE server or client container.

Source: J2EE v1.4 Glossary
    

Question: What are the contents of web module?
Answer: A web module may contain:
a) JSP files
b) Java classes
c) gif and html files and
d) web component deployment descriptors
  

Question: Differentiate between .ear,  .jar and .war files.
Answer: These files are simply zipped file using java jar tool. These files are created for different purposes. Here is the description of these files:
.jar files: These files are with the .jar extenstion. The .jar files contains the libraries, resources and accessories files like property files.
.war files: These files are with the .war extension. The war file contains the web application that can be deployed on the any servlet/jsp container. The .war file contains jsp, html, javascript and other files for necessary for the development of web applications.
.ear files: The .ear file contains the EJB modules of the application.
  

Question: What is the difference between Session Bean and Entity Bean?
Answer:
Session Bean: Session is one of the EJBs and it represents a single client inside the Application Server. Stateless session is easy to develop and its efficient. As compare to entity beans session beans require few server resources.

A session bean is similar to an interactive session and is not shared; it can have only one client, in the same way that an interactive session can have only one user. A session bean is not persistent and it is destroyed once the session terminates.
 
Entity Bean: An entity bean represents persistent global data from the database. Entity beans data are stored into database.
    

Question: Why J2EE is suitable for the development distributed multi-tiered enterprise applications?
Answer: The J2EE platform consists of multi-tiered distributed application model. J2EE applications allows the developers to design and implement the business logic into components according to business requirement. J2EE architecture allows the development of multi-tired applications and the developed applications can be installed on different machines depending on the tier in the multi-tiered J2EE environment . The J2EE application parts are:

a) Client-tier components run on the client machine.
b) Web-tier components run on the J2EE server.
c) Business-tier components run on the J2EE server and the
d) Enterprise information system (EIS)-tier software runs on the EIS servers
    

Question: Why do understand by a container?
Answer: Normally, thin-client multi-tiered applications are hard to write because they involve many lines of intricate code to handle transaction and state management, multithreading, resource pooling, and other complex low-level details. The component-based and platform-independent J2EE architecture makes J2EE applications easy to write because business logic is organized into reusable components. In addition, the J2EE server provides underlying services in the form of a container for every component type. Because you do not have to develop these services yourself, you are free to concentrate on solving the business problem at hand (Source: http://java.sun.com/j2ee/1.3/docs/tutorial/doc/Overview4.html ).

In short containers are the interface between a component and the low-level platform specific functionality that supports the component. The application like Web, enterprise bean, or application client component must be assembled and deployed on the J2EE container before executing.
  

Question: What are the services provided by a container?
Answer: The services provided by container are as follows:
a) Transaction management for the bean
b) Security for the bean
c) Persistence of the bean
d) Remote access to the bean
e) Lifecycle management of the bean
f) Database-connection pooling
g) Instance pooling for the bean
   

Question: What are types of J2EE clients?
Answer: J2EE clients are the software that access the services components installed on the J2EE container. Following are the J2EE clients:
a) Applets
b) Java-Web Start clients
c) Wireless clients
d) Web applications

1. What do you understand by the term J2EE?
J2EE is a specification. provides middleware services.
EJB JDBC JNDI JMS JavaMail JTA Servlets JSPs Connectors JAAS

EJB : is Server Side component architecture for developing distributed applications.
Developers need to concentrate only on business logic.
The middleware services are provided by appserver.
(transaction management,persistence, threading,concurreny )


Session Beans : Model processes
Entity Beans : Model data
Message Driven beans : Similar to session beans. Invoked only by sending messages.

2. Diff between RMI and EJB

EJB uses RMI technology.
We have to declare the middleware services needed by the EJB in a descriptor.
The Appserver will generate stubs for the same.

RMI : one has to write the middleware services. (txn mgmt, persitence.)

EJB cannot be invoked directly by remote clients because there are not network enabled.
Location transparency.


3. How many tiers does an J2EE application have? Explain multi-tier applications?

4. What is a web component?
A web componenet is a software entity which runs on a web server, handles requests and generates dynamic web content.

5. What is a web container?
Runtime environment for servlets and jsp
Manages lifecycle of instances
Supports HTTP

6. Should web container always be a part of web server?
No.

7.What are servlets?
8. What are JSP’s?
9.What are web services?
10.Explain SOA?
11. Explain EJB containers?
12.What is the purpose of init() in servlet class?

13. Can servlets have constructors? Can they be used for initializing servlets instead of init()
Yes. But we shouldn’t. Reason being init has access to servlet config and servlet context object , constructors won’t.

14.Name JSP scripting elements?
declarations, scriptlets, expressions.

15.What is SingleThreadModel ?
16. How to implement a thread-safe JSP page? What directive should be added?

‹ %@ page isThreadSafe="false" %

17 .How can we include static files within a JSP page?
Answer: using the JSP include directive.

18.Distinguish between servletconfig and servlet context?
19.What is the difference in between doPost and doGet methods ?
20.Why does EJB needs two interface( Home and Remote Interface) ?
21.Explain deployment descriptors?
22.Why cant we invoke methods on ejbs directly ?
23.Explain clustering and fault tolerance
24.How would you go about analyzing performance of the application

Application performance testing

When performance testing a Web application, several requirements must be
determined either through interpretation of data from an existing application that
performs similar work. Those requirements are:

User base
What is the expected number of users that will access this application? This is
generally expressed in hits per month, day, hour, or minute depending on
volumes.

Total concurrent users

During a peak interval, what is the maximum possible number of users
accessing the application at the same time.

Peak request rate
How many pages will need to be served per second?