Java Fundmental-VII

1. Do I need to use synchronized on setValue(int)?

Ans : It depends whether the method affects method local variables, class static or instance variables. If only method local variables are changed, the value is said to be confined by the method and is not prone to threading issues.
2. Do I need to use synchronized on setValue(int)?

Ans : It depends whether the method affects method local variables, class static or instance variables. If only method local variables are changed, the value is said to be confined by the method and is not prone to threading issues.
3. What is the SwingUtilities.invokeLater(Runnable) method for?

Ans : The static utility method invokeLater(Runnable) is intended to execute a new runnable thread from a Swing application without disturbing the normal sequence of event dispatching from the Graphical User Interface (GUI). The method places the runnable object in the queue of Abstract Windowing Toolkit (AWT) events that are due to be processed and returns immediately. The runnable object’s run() method is only called when it reaches the front of the queue. The deferred effect of the invokeLater(Runnable) method ensures that any necessary updates to the user interface can occur immediately, and the runnable work will begin as soon as those high priority events are dealt with. The invoke later method might be used to start work in response to a button click that also requires a significant change to the user interface, perhaps to restrict other activities, while the runnable thread executes.
4. What is the volatile modifier for?

Ans : The volatile modifier is used to identify variables whose values should not be optimized by the Java Virtual Machine, by caching the value for example. The volatile modifier is typically used for variables that may be accessed or modified by numerous independent threads and signifies that the value may change without synchronization.
5. Which class is the wait() method defined in?

Ans : The wait() method is defined in the Object class, which is the ultimate superclass of all others. So the Thread class and any Runnable implementation inherit this method from Object. The wait() method is normally called on an object in a multi-threaded program to allow other threads to run. The method should should only be called by a thread that has ownership of the object’s monitor, which usually means it is in a synchronized method or statement block.
6. Which class is the wait() method defined in?

Ans : I get incompatible return type for my thread’s getState( ) method! - It sounds like your application was built for a Java software development kit before Java 1.5. The Java API Thread class method getState() was introduced in version 1.5. Your thread method has the same name but different return type. The compiler assumes your application code is attempting to override the API method with a different return type, which is not allowed, hence the compilation error.
7. What is a working thread?

Ans : A working thread, more commonly known as a worker thread is the key part of a design pattern that allocates one thread to execute one task. When the task is complete, the thread may return to a thread pool for later use. In this scheme a thread may execute arbitrary tasks, which are passed in the form of a Runnable method argument, typically execute(Runnable). The runnable tasks are usually stored in a queue until a thread host is available to run them. The worker thread design pattern is usually used to handle many concurrent tasks where it is not important which finishes first and no single task needs to be coordinated with another. The task queue controls how many threads run concurrently to improve the overall performance of the system. However, a worker thread framework requires relatively complex programming to set up, so should not be used where simpler threading techniques can achieve similar results.
8. What is a green thread?

Ans : A green thread refers to a mode of operation for the Java Virtual Machine (JVM) in which all code is executed in a single operating system thread. If the Java program has any concurrent threads, the JVM manages multi-threading internally rather than using other operating system threads. There is a significant processing overhead for the JVM to keep track of thread states and swap between them, so green thread mode has been deprecated and removed from more recent Java implementations. Current JVM implementations make more efficient use of native operating system threads.
9. What are native operating system threads?

Ans : Native operating system threads are those provided by the computer operating system that plays host to a Java application, be it Windows, Mac or GNU/Linux. Operating system threads enable computers to run many programs simultaneously on the same central processing unit (CPU) without clashing over the use of system resources or spending lots of time running one program at the expense of another. Operating system thread management is usually optimised to specific microprocessor architecture and features so that it operates much faster than Java green thread processing.

Java Fundamental-VI

1. 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.


2. What is the difference between the Boolean & operator and the && operator?
- If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.


3. How many times may an object's finalize() method be invoked by the garbage collector?
An object's finalize() method may only be invoked once by the garbage collector.


4. 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.


5. What is the argument type of a program s main() method?
A program's main() method takes an argument of the String[] type.


6. Which Java operator is right associative?
The = operator is right associative.


7. Can a double value be cast to a byte?
Yes, a double value can be cast to a byte.


8. What is the difference between a break statement and a continue statement?
A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.


9. 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.


10. What is the advantage of the event-delegation model over the earlier event-inheritance model?
The event-delegation model has two advantages over the event-inheritance model. First, it enables event handling to be handled by objects other than the ones that generate the events (or their containers). This allows a clean separation between a component s design and its use. The other advantage of the event-delegation model is that 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 repeatedly process unhandled events, as is the case of the event-inheritance model.

Java Fundamental-V

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1. What is the use of preparedstatement?

Preparedstatements are precompiled statements. It is mainly used to speed up the process of inserting/updating/deleting especially when there is a bulk processing.


2. What is callable statement? Tell me the way to get the callable statement?

Callablestatements are used to invoke the stored procedures. You can obtain the callablestatement from Connection using the following methods prepareCall(String sql) prepareCall(String sql, int resultSetType, int resultSetConcurrency)


3. In a statement, I am executing a batch. What is the result of the execution?

It returns the int array. The array contains the affected row count in the corresponding index of the SQL.


4. Can a abstract method have the static qualifier?

No


5.. What are the different types of qualifier and what is the default qualifier?

public, protected, private, package (default)


6. What is the super class of Hashtable?

Dictionary

Java Fundamental-IV

1. 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

2. What do you understand by JTA and JTS?

Answer: JTA stands for Java Transaction API and JTS stands for Java Transaction Service. JTA provides a standard interface which allows the developers to demarcate transactions in a manner that is independent of the transaction manager implementation. The J2EE SDK uses the JTA transaction manager to implement the transaction. The code developed by developers does not calls the JTS methods directly, but only invokes the JTA methods. Then JTA internally invokes the JTS routines. JTA is a high level transaction interface used by the application code to control the transaction.

Java Fundamental-III

1. When should the method invokeLater()be used?

This method is used to ensure that Swing components are updated through the event-dispatching thread.

2. How can a subclass call a method or a constructor defined in a superclass?

Use the following syntax: super.myMethod(); To call a constructor of the superclass, just write super(); in the first line of the subclass’s constructor.

3. What’s the difference between a queue and a stack?

Stacks works by last-in-first-out rule (LIFO), while queues use the FIFO rule.

4. You can create an abstract class that contains only abstract methods. On the other hand, you can create an interface that declares the same methods. So can you use abstract classes instead of interfaces?

Sometimes. But your class may be a descendent of another class and in this case the interface is your only option.

5. What comes to mind when you hear about a young generation in Java?

Garbage collection.

6. What comes to mind when someone mentions a shallow copy in Java?

Object cloning.

7. If you’re overriding the method equals() of an object, which other method you might also consider?

hashCode()

8. You are planning to do an indexed search in a list of objects. Which of the two Java collections should you use: ArrayList or LinkedList?

ArrayList

9. How would you make a copy of an entire Java object with its state?

Have this class implement Cloneable interface and call its method clone().

10. How can you minimize the need of garbage collection and make the memory use more effective?

Use object pooling and weak object references.

11. There are two classes: A and B. The class B need to inform a class A when some important event has happened. What Java technique would you use to implement it?

If these classes are threads I’d consider notify() or notifyAll(). For regular classes you can use the Observer interface.

12. What access level do you need to specify in the class declaration to ensure that only classes from the same directory can access it?

You do not need to specify any access level, and Java will use a default package access level

13. 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 descriptor

14. 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.

15. 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.

16. 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

17. 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.

18. 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

Database System-I

1.What is foreign Key? What is its purpose?

A non key attribute, whose value are derived from the primary key of some other table, is known as foreign key in the current table.The table in which this non-key attribute i.e. foreign key attribute exists, is called a foreign table.

2.Define the terms  Tuple and  Attribute

Tuples: The rows of tables (relations) are generally referred to as tuples. Attribute: The columns of tables are generally referred to as attribute.

3.What do you understand by the terms Cardinality and Degree of the table?

Degree: The number of attributes in a relation determines the degree of a relation. A relation having 3 attributes is said to be a relation of degree 3.

Cardinality: The number of rows in a relation is known as Cardinality.

4.What is the main function of DBA.

The DBA must be a manager, more than a technician-seeking to meet the needs of people who use the data. Since many user may share the same data resource, the DBA must be prepared to meet the need and objective.

5.Write a query on the customers table whose output will exclude all customers with a rating <=100, unless they are located in Shimla.

SELECT *  FROM customers  WHERE rating >100 OR city =’Shimla’ ;

6.Write a query that selects all orders except those zeros or NULLs in  the amount field.

SELECT * FROM Orders  WHERE amt < >0  AND (amt IS NOT NULL) ;

7.Write a query that lists customers in descending order of rating. Output the rating field first, followed by the customer’s name and number.

SELECT rating, cust-name, cust-num FROM customers ORDER BY rating DESC;

8.Write a command that puts the following values, in their given order, into the salesman table: cust-name-Manisha, city-Manali, comm.- NULL, cust-num-1901.

INSERT INTO salesman (city, cust-name, comm.,cust-num)VALUES(‘Manisha’,NULL,1901) ;

9.What are DDL and DML?

The DDL provides statements for the creation and deletion of tables and indexes.

The DML provides statements to enter, update, delete data and perform complex queries on these tables.

10.What is the difference between Where and Having Clause?

The HAVING clause places the condition on group but WHERE clause places the condition on individual rows

11.What do you understand by constraints?

Constraints are used to enforce rules at table level when ever row is inserted, updated/deleted from table.

Constraints can be defined to one of the Two level.

Column Level: Reference to a single column. can be defined any type of integrity.

Table Level: References one or more columns and is defined separately from definition of the columns in the table.

12.Write some features of SQL?

Recovery ad Concurrency:- Concurrency is concerned with the manner in which multiple user operate upon the Database.

Security: The Security can be maintained by view mechanism.

Integrity Constraints-> Integrity constraints are enforced by the system.

13.Write various database objects available in SQL?

Table: A Table is used to store Data

View: A view is the temporary table created using Original table.

Sequence:   Sequences are used to generate Primary key value.

Index:  They are used to improve queries.

Synonym: They give alternative names to objects.     

14.Write the rules to name an objects?

The maximum length must be 30 character long.

The Object name  should not contain quotation mark.

The name must start with letter.

The use of $ and # is discouraged in the object name.

A name must not be a reserved name.

15.What are group Functions?

The aggregate functions are group functions. They return result based on groups of rows. The group functions are

AVG(), COUNT(), MAX(),  MIN(), SUM()

16.What are  column alias?

In many  cases heading table may not be descriptive and hence it difficult to understand. In  such case we use columns alias It will change column heading with column alias.

Computer Network-IV

Q.1 What is protocol? How many types of protocols are there?

Ans. When computers communicate each other, there needs to be a common set of rules and instructions that each computer follows. A specific set of communication rules is called a protocol.

Some protocol: PPP, HTTP, SLIP, FTP, TCP/IP

Q.2 What is the difference between Networking and Remote Networking?

Ans. The main difference between Networking and Remote Networking, is the network which we use in offices or other places locally such LAN or INTERNET and remote networking is one which we use TERMINAL Services to communicate with the remote users such WAN.

Q.3 What is point-to-point protocol?

Ans. A communication protocol used to connect computer to remote networking services include Internet Service Providers. In networking, the Point-to-Point protocol is commonly used to establish a direct connection between two nodes. Its primary use has been to connect computers using a phone line.

Computer Network-III

1. What is packet filter?
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.

2. What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.

3. What is multicast routing?
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.

Computer Network-II

1. What is Bandwidth?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth.

2. What are the types of Transmission media?
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
Guided Media:
These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
b) Unguided Media:
This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.

3. What is Project 802?
It is a project started by IEEE to set standards to enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN protocols.
It consists of the following:
802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.
Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.

Operating System-IV

1. Describe the Buddy system of memory allocation.

Free memory is maintained in linked lists, each of equal sized blocks. Any such block is of size 2^k. When some memory is required by a process, the block size of next higher order is chosen, and broken into two. Note that the two such pieces differ in address only in their kth bit. Such pieces are called buddies. When any used block is freed, the OS checks to see if its buddy is also free. If so, it is rejoined, and put into the original free-block linked-list.

Operating System-III

1. What is an Operating System (OS)?

An operating system is basically software that makes everything in the computer work together smoothly and efficiently. Basically, it controls the "overall" activity of a computer.

Operating systems have three basic jobs they must do:

•Control Hardware - The operating system controls all the parts of the computer and attempts to get everything working together.

•Run Applications - Another job the OS does is run application software. This would include Microsoft Office, WinZip, games, etc.

•Manage Data and Files - The OS makes it easy for you to organize your computer. Through the OS you are able to do a number of things to data including copy, move, delete, and rename it. This makes it much easier to find and organize what you have.

Operating System-II

1. What is DRAM? In which form does it store data? - DRAM is not the best, but it’s cheap, does the job, and is available almost everywhere you look. DRAM data resides in a cell made of a capacitor and a transistor. The capacitor tends to lose data unless it’s recharged every couple of milliseconds, and this recharging tends to slow down the performance of DRAM compared to speedier RAM types.

UNIX O/S Tutorial-III

1. What is the difference between Swapping and Paging?
Swapping:
Whole process is moved from the swap device to the main memory for execution. Process size must be less than or equal to the available main memory. It is easier to implementation and overhead to the system. Swapping systems does not handle the memory more flexibly as compared to the paging systems.
Paging:

UNIX O/S Tutorial-II

1. Brief about the initial process sequence while the system boots up.
While booting, special process called the 'swapper' or 'scheduler' is created with Process-ID 0. The swapper manages memory allocation for processes and influences CPU allocation. The swapper inturn creates 3 children:
the process dispatcher,
vhand and
dbflush
with IDs 1,2 and 3 respectively.
This is done by executing the file /etc/init. Process dispatcher gives birth to the shell. Unix keeps track of all the processes in an internal data structure called the Process Table (listing command is ps -el).

UNIX O/S Tutorial

1. How are devices represented in UNIX?

All devices are represented by files called special files that are located in/dev directory. Thus, device files and other files are named and accessed in the same way. A 'regular file' is just an ordinary data file in the disk. A 'block special file' represents a device with characteristics similar to a disk (data transfer in terms of blocks). A 'character special file' represents a device with characteristics similar to a keyboard (data transfer is by stream of bits in sequential order).

2. What is 'inode'?

All UNIX files have its description stored in a structure called 'inode'. The inode contains info about the file-size, its location, time of last access, time of last modification, permission and so on. Directories are also represented as files and have an associated inode. In addition to descriptions about the file, the inode contains pointers to the data blocks of the file. If the file is large, inode has indirect pointer to a block of pointers to additional data blocks (this further aggregates for larger files). A block is typically 8k.

Inode consists of the following fields:

 File owner identifierØ

 File typeØ

 File access permissionsØ

 File access timesØ

 Number of linksØ

 File sizeØ

 Location of the file dataØ

3. Brief about the directory representation in UNIX

A Unix directory is a file containing a correspondence between filenames and inodes. A directory is a special file that the kernel maintains. Only kernel modifies directories, but processes can read directories. The contents of a directory are a list of filename and inode number pairs. When new directories are created, kernel makes two entries named '.' (refers to the directory itself) and '..' (refers to parent directory).

System call for creating directory is mkdir (pathname, mode).

4. What are the Unix system calls for I/O?

 open(pathname,flag,mode) - open fileØ

 creat(pathname,mode) - create fileØ

 close(filedes) - close an open fileØ

 read(filedes,buffer,bytes) - read data from an open fileØ

 write(filedes,buffer,bytes) - write data to an open fileØ

 lseek(filedes,offset,from) - position an open fileØ

 dup(filedes) - duplicate an existing file descriptorØ

 dup2(oldfd,newfd) - duplicate to a desired file descriptorØ

 fcntl(filedes,cmd,arg) - change properties of an open fileØ

 ioctl(filedes,request,arg) - change the behaviour of an open fileØ

The difference between fcntl anf ioctl is that the former is intended for any open file, while the latter is for device-specific operations.

5. How do you change File Access Permissions?

Every file has following attributes:

 owner's user ID ( 16 bit integer )Ø

 owner's group ID ( 16 bit integer )Ø

 File access mode wordØ

'r w x -r w x- r w x'

(user permission-group permission-others permission)

r-read, w-write, x-execute

To change the access mode, we use chmod(filename,mode).

Example 1:

To change mode of myfile to 'rw-rw-r--' (ie. read, write permission for user - read,write permission for group - only read permission for others) we give the args as:

chmod(myfile,0664) .

Each operation is represented by discrete values

'r' is 4

'w' is 2

'x' is 1

Therefore, for 'rw' the value is 6(4+2).

Example 2:

To change mode of myfile to 'rwxr--r--' we give the args as:

chmod(myfile,0744).

6. What are links and symbolic links in UNIX file system?

A link is a second name (not a file) for a file. Links can be used to assign more than one name to a file, but cannot be used to assign a directory more than one name or link filenames on different computers.

Symbolic link 'is' a file that only contains the name of another file.Operation on the symbolic link is directed to the file pointed by the it.Both the limitations of links are eliminated in symbolic links.

Commands for linking files are:

Link ln filename1 filename2

Symbolic link ln -s filename1 filename2

7. What is a FIFO?

FIFO are otherwise called as 'named pipes'. FIFO (first-in-first-out) is a special file which is said to be data transient. Once data is read from named pipe, it cannot be read again. Also, data can be read only in the order written. It is used in interprocess communication where a process writes to one end of the pipe (producer) and the other reads from the other end (consumer).

8. How do you create special files like named pipes and device files?

The system call mknod creates special files in the following sequence.

1. kernel assigns new inode,

2. sets the file type to indicate that the file is a pipe, directory or special file,

3. If it is a device file, it makes the other entries like major, minor device numbers.

For example:

If the device is a disk, major device number refers to the disk controller and minor device number is the disk.

9. Discuss the mount and unmount system calls

The privileged mount system call is used to attach a file system to a directory of another file system; the unmount system call detaches a file system. When you mount another file system on to your directory, you are essentially splicing one directory tree onto a branch in another directory tree. The first argument to mount call is the mount point, that is , a directory in the current file naming system. The second argument is the file system to mount to that point. When you insert a cdrom to your unix system's drive, the file system in the cdrom automatically mounts to /dev/cdrom in your system.

10. How does the inode map to data block of a file?

Inode has 13 block addresses. The first 10 are direct block addresses of the first 10 data blocks in the file. The 11th address points to a one-level index block. The 12th address points to a two-level (double in-direction) index block. The 13th address points to a three-level(triple in-direction)index block. This provides a very large maximum file size with efficient access to large files, but also small files are accessed directly in one disk read.

11. What is a shell?

A shell is an interactive user interface to an operating system services that allows an user to enter commands as character strings or through a graphical user interface. The shell converts them to system calls to the OS or forks off a process to execute the command. System call results and other information from the OS are presented to the user through an interactive interface. Commonly used shells are sh,csh,ks etc.

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