Showing posts with label Technical Interview. Show all posts
Showing posts with label Technical Interview. Show all posts

Wednesday, May 06, 2009

Java Fundamental-II

1. What is a Marker Interface?

An interface with no methods. Example: Serializable, Remote, Cloneable


2. What interface do you implement to do the sorting?

Comparable


3. What is the eligibility for a object to get cloned?

It must implement the Cloneable interface


4. What is the purpose of abstract class?

It is not an instantiable class. It provides the concrete implementation for some/all the methods. So that they can reuse the concrete functionality by inheriting the abstract class.


5. What is the difference between interface and abstract class?

Abstract class defined with methods. Interface will declare only the methods. Abstract classes are very much useful when there is a some functionality across various classes. Interfaces are well suited for the classes which varies in functionality but with the same method signatures.


6. What do you mean by RMI and how it is useful?

RMI is a remote method invocation. Using RMI, you can work with remote object. The function calls are as though you are invoking a local variable. So it gives you a impression that you are working really with a object that resides within your own JVM though it is somewhere.


7. What is the protocol used by RMI?

RMI-IIOP


8. What is a hashCode?

hash code value for this object which is unique for every object.


9. What is a thread?

Thread is a block of code which can execute concurrently with other threads in the JVM.


10. What is the algorithm used in Thread scheduling?

Fixed priority scheduling.


11. What is hash-collision in Hashtable and how it is handled in Java?

Two different keys with the same hash value. Two different entries will be kept in a single hash bucket to avoid the collision.


12. What are the different driver types available in JDBC?

1. A JDBC-ODBC bridge 2. A native-API partly Java technology-enabled driver 3. A net-protocol fully Java technology-enabled driver 4. A native-protocol fully Java technology-enabled driver For more information: Driver Description


13. Is JDBC-ODBC bridge multi-threaded?

No


14. Does the JDBC-ODBC Bridge support multiple concurrent open statements per connection?

No


15. What is the use of serializable?

To persist the state of an object into any perminant storage device.


16. What is the use of transient?

It is an indicator to the JVM that those variables should not be persisted. It is the users responsibility to initialize the value when read back from the storage.


17. What are the different level lockings using the synchronization keyword?

Class level lock Object level lock Method level lock Block level lock

Thursday, April 30, 2009

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.

Tuesday, April 21, 2009

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.

Monday, April 20, 2009

Operating System-I

1. What are the basic functions of an operating system? - Operating system controls and coordinates the use of the hardware among the various applications programs for various uses. Operating system acts as resource allocator and manager. Since there are many possibly conflicting requests for resources the operating system must decide which requests are allocated resources to operating the computer system efficiently and fairly. Also operating system is control program which controls the user programs to prevent errors and improper use of the computer. It is especially concerned with the operation and control of I/O devices.

2. Why paging is used? - Paging is solution to external fragmentation problem which is to permit the logical address space of a process to be noncontiguous, thus allowing a process to be allocating physical memory wherever the latter is available.

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

4. What resources are used when a thread created? How do they differ from those when a process is created? - When a thread is created the threads does not require any new resources to execute the thread shares the resources like memory of the process to which they belong to. The benefit of code sharing is that it allows an application to have several different threads of activity all within the same address space. Whereas if a new process creation is very heavyweight because it always requires new address space to be created and even if they share the memory then the inter process communication is expensive when compared to the communication between the threads.

5. What is virtual memory? - Virtual memory is hardware technique where the system appears to have more memory that it actually does. This is done by time-sharing, the physical memory and storage parts of the memory one disk when they are not actively being used.

6. What is Throughput, Turnaround time, waiting time and Response time? - Throughput – number of processes that complete their execution per time unit. Turnaround time – amount of time to execute a particular process. Waiting time – amount of time a process has been waiting in the ready queue. Response time – amount of time it takes from when a request was submitted until the first response is produced, not output (for time-sharing environment).

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

8. What is the important aspect of a real-time system or Mission Critical Systems? - A real time operating system has well defined fixed time constraints. Process must be done within the defined constraints or the system will fail. An example is the operating system for a flight control computer or an advanced jet airplane. Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems. Real-Time systems may be either hard or soft real-time. Hard real-time: Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM), Conflicts with time-sharing systems, not supported by general-purpose operating systems. Soft real-time: Limited utility in industrial control of robotics, Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.

9. What is the difference between Hard and Soft real-time systems? - A hard real-time system guarantees that critical tasks complete on time. This goal requires that all delays in the system be bounded from the retrieval of the stored data to the time that it takes the operating system to finish any request made of it. A soft real time system where a critical real-time task gets priority over other tasks and retains that priority until it completes. As in hard real time systems kernel delays need to be bounded.

10. What is the cause of thrashing? How does the system detect thrashing? Once it detects thrashing, what can the system do to eliminate this problem? - Thrashing is caused by under allocation of the minimum number of pages required by a process, forcing it to continuously page fault. The system can detect thrashing by evaluating the level of CPU utilization as compared to the level of multiprogramming. It can be eliminated by reducing the level of multiprogramming.

11. What is multi tasking, multi programming, multi threading? - Multi programming: Multiprogramming is the technique of running several programs at a time using timesharing. It allows a computer to do several things at the same time. Multiprogramming creates logical parallelism. The concept of multiprogramming is that the operating system keeps several jobs in memory simultaneously. The operating system selects a job from the job pool and starts executing a job, when that job needs to wait for any i/o operations the CPU is switched to another job. So the main idea here is that the CPU is never idle. Multi tasking: Multitasking is the logical extension of multiprogramming .The concept of multitasking is quite similar to multiprogramming but difference is that the switching between jobs occurs so frequently that the users can interact with each program while it is running. This concept is also known as time-sharing systems. A time-shared operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of time-shared system. Multi threading: An application typically is implemented as a separate process with several threads of control. In some situations a single application may be required to perform several similar tasks for example a web server accepts client requests for web pages, images, sound, and so forth. A busy web server may have several of clients concurrently accessing it. If the web server ran as a traditional single-threaded process, it would be able to service only one client at a time. The amount of time that a client might have to wait for its request to be serviced could be enormous. So it is efficient to have one process that contains multiple threads to serve the same purpose. This approach would multithread the web-server process, the server would create a separate thread that would listen for client requests when a request was made rather than creating another process it would create another thread to service the request. To get the advantages like responsiveness, Resource sharing economy and utilization of multiprocessor architectures multithreading concept can be used.
12. What is hard disk and what is its purpose? - Hard disk is the secondary storage device, which holds the data in bulk, and it holds the data on the magnetic medium of the disk.Hard disks have a hard platter that holds the magnetic medium, the magnetic medium can be easily erased and rewritten, and a typical desktop machine will have a hard disk with a capacity of between 10 and 40 gigabytes. Data is stored onto the disk in the form of files.

13. What is fragmentation? Different types of fragmentation? - Fragmentation occurs in a dynamic memory allocation system when many of the free blocks are too small to satisfy any request. External Fragmentation: External Fragmentation happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. If too much external fragmentation occurs, the amount of usable memory is drastically reduced. Total memory space exists to satisfy a request, but it is not contiguous. Internal Fragmentation: Internal fragmentation is the space wasted inside of allocated memory blocks because of restriction on the allowed sizes of allocated blocks. Allocated memory may be slightly larger than requested memory; this size difference is memory internal to a partition, but not being use.

Search Aptipedia