Java Fundamental-I

1. How could Java classes direct program messages to the system console, but error messages, say to a file?

The class System has a variable out that represents the standard output, and the variable err that represents the standard error device. By default, they both point at the system console. This how the standard output could be re-directed:

Stream st =

new Stream (new

FileOutputStream ("techinterviews_com.txt"));

System.setErr(st);

System.setOut(st);


2. What’s the difference between an interface and an abstract class?

An abstract class may contain code in method bodies, which is not allowed in an interface. With abstract classes, you have to inherit your class from it and Java does not allow multiple inheritance. On the other hand, you can implement multiple interfaces in your class.


3. Why would you use a synchronized block vs. synchronized method?

Synchronized blocks place locks for shorter periods than synchronized methods.


4. Explain the usage of the keyword transient?

This keyword indicates that the value of this member variable does not have to be serialized with the object. When the class will be de-serialized, this variable will be initialized with a default value of its data type (i.e. zero for integers).


5. How can you force garbage collection?

You can’t force GC, but could request it by calling System.gc(). JVM does not guarantee that GC will be started immediately.


6. How do you know if an explicit object casting is needed?

If you assign a superclass object to a variable of a subclass’s data type, you need to do explicit casting. For example:

Object a;Customer b; b = (Customer) a;

When you assign a subclass to a variable having a supeclass type, the casting is performed automatically.


7. What’s the difference between the methods sleep() and wait()

The code sleep(1000); puts thread aside for exactly one second. The code wait(1000), causes a wait of up to one second. A thread could stop waiting earlier if it receives the notify() or notifyAll() call. The method wait() is defined in the class Object and the method sleep() is defined in the class Thread.


8. Can you write a Java class that could be used both as an applet as well as an application?

Yes. Add a main() method to the applet.


9. What’s the difference between constructors and other methods?

Constructors must have the same name as the class and can not return a value. They are only called once while regular methods could be called many times.



10. Can you call one constructor from another if a class has multiple constructors

Yes. Use this() syntax.


11. Explain the usage of Java packages.

This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. Packages access level also allows you to protect data from being used by the non-authorized classes.


12. If a class is located in a package, what do you need to change in the OS environment to be able to use it?

You need to add a directory or a jar file that contains the package directories to the CLASSPATH environment variable. Let’s say a class Employee belongs to a package com.xyz.hr; and is located in the file c:/dev/com.xyz.hr.Employee.java. In this case, you’d need to add c:/dev to the variable CLASSPATH. If this class contains the method main(), you could test it from a command prompt window as follows:

c:\>java com.xyz.hr.Employee


13. What’s the difference between J2SDK 1.5 and J2SDK 5.0?

There’s no difference, Sun Microsystems just re-branded this version.


14. What would you use to compare two String variables - the operator == or the method equals()?

I’d use the method equals() to compare the values of the Strings and the = = to check if two variables point at the same instance of a String object.


15. Does it matter in what order catch statements for FileNotFoundException and IOExceptipon are written?

Yes, it does. The FileNoFoundException is inherited from the IOException. Exception’s subclasses have to be caught first.


16. Can an inner class declared inside of a method access local variables of this method?

It’s possible if these variables are final.


17. What can go wrong if you replace && with & in the following code:

String a=null;

if (a!=null && a.length()>10)

{...}

A single ampersand here would lead to a NullPointerException.


18. What’s the main difference between a Vector and an ArrayList

Java Vector class is internally synchronized and ArrayList is not.

Computer Network-I

1. What are the two types of transmission technology available?
(i) Broadcast and (ii) point-to-point

2. What is subnet?
A generic term for section of a large networks usually separated by a bridge or router.

3. Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc.
Communication means the meaning full exchange of information between two communication media.

4. What are the possible ways of data exchange?
(i) Simplex (ii) Half-duplex (iii) Full-duplex.

5. What is SAP?
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.

6. What do you meant by "triple X" in Networks?
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X"

7. What is frame relay, in which layer it comes?
Frame relay is a packet switching technology. It will operate in the data link layer.

8. What is terminal emulation, in which layer it comes?
Telnet is also called as terminal emulation. It belongs to application layer.

9. What is Beaconing?
The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.

10. What is redirector?
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.

11. What is NETBIOS and NETBEUI?
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.

12. What is RAID?
A method for providing fault tolerance by using multiple hard disk drives.

13. What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.

14. What is Brouter?
Hybrid devices that combine the features of both bridges and routers.

15. What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.

16. What is point-to-point protocol?
A communications protocol used to connect computers to remote networking services including Internet service providers.

17. How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats

18. What is attenuation?
The degeneration of a signal over distance on a network cable is called attenuation.

19. What is MAC address?
The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.

20. Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.
baud rate = bit rate / N
where N is no-of-bits represented by each signal shift.