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Core Java Interview Questions with Answers -2

November 20th, 2007

16. How does Java handle integer overflows and underflows?

It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

17. What is the Vector class?

The Vector class provides the capability to implement a growable array of objects

18. What modifiers may be used with an inner class that is a member of an outer class?

A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.

19. What is an Iterator interface?

The Iterator interface is used to step through the elements of a Collection.

20. What is the difference between the >> and >>> operators?

The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out.

21. Which method of the Component class is used to set the position and size of a component?

setBounds()

22. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?

Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.

23What is the difference between yielding and sleeping?

When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.

24. Which java.util classes and interfaces support event handling?

The EventObject class and the EventListener interface support event processing.

25. Is sizeof a keyword?

The sizeof operator is not a keyword.

26. What are wrapped classes?

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

27. Does garbage collection guarantee that a program will not run out of memory?

Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection

28. What restrictions are placed on the location of a package statement within a source code file?

A package statement must appear as the first line in a source code file (excluding blank lines and comments).

29. Can an object’s finalize() method be invoked while it is reachable?

An object’s finalize() method cannot be invoked by the garbage collector while the object is still reachable. However, an object’s finalize() method may be invoked by other objects.

30. What is the immediate superclass of the Applet class?

Panel

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Core Java Interview Questions with Answers

November 19th, 2007

Core Java Interview Questions with Answers

1.what is a transient variable?

A transient variable is a variable that may not be serialized.

2.which containers use a border Layout as their default layout?

The window, Frame and Dialog classes use a border layout as their default layout.

3.Why do threads block on I/O?

Threads block on i/o (that is enters the waiting state) so that other threads may execute while the i/o Operation is performed.

4. How are Observer and Observable used?

Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.

5. What is synchronization and why is it important?

With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object’s value. This often leads to significant errors.

6. Can a lock be acquired on a class?

Yes, a lock can be acquired on a class. This lock is acquired on the class’s Class object.

7. What’s new with the stop(), suspend() and resume() methods in JDK 1.2?

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

8. Is null a keyword?

The null value is not a keyword.

9. What is the preferred size of a component?

The preferred size of a component is the minimum component size that will allow the component to display normally.

10. What method is used to specify a container’s layout?

The setLayout() method is used to specify a container’s layout.

11. Which containers use a FlowLayout as their default layout?

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

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

When a thread terminates its processing, it enters the dead state.

13. What is the Collections API?

The Collections API is a set of classes and interfaces that support operations on collections of objects.

14. Which characters may be used as the second character of an identifier, but not as the first character of an identifier?

The digits 0 through 9 may not be used as the first character of an identifier but they may be used after the first character of an identifier.

15. What is the List interface?

The List interface provides support for ordered collections of objects.

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to be continued……

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Custom Networking

November 18th, 2007

Custom Networking

The Java platform is highly regarded in part because of its suitability for writing programs that use and interact with the resources on the Internet and the World Wide Web. In fact, Java-compatible browsers use this ability of the Java platform to the extreme to transport and run applets over the Internet.
This trail walks you through the complexities of writing Java applications and applets that can be used on the Internet.

Overview of Networking has two sections. The first describes the networking capabilities of the Java platform that you may already be using without realizing that you are using the network. The second provides a brief overview of networking to familiarize you with terms and concepts that you should understand before reading how to use URLs, sockets, and datagrams.

Working With URLs discusses how your Java programs can use URLs to access information on the Internet. A URL (Uniform Resource Locator) is the address of a resource on the Internet. Your Java programs can use URLs to connect to and retrieve information over a network. This lesson provides a more complete definition of a URL and shows you how to create and parse a URL, how to open a connection to a URL, and how to read from and write to that connection.

All About Sockets explains how to use sockets so that your programs can communicate with other programs on the network. A socket is one endpoint of a two-way communication link between two programs running on the network. This lesson shows you how a client can connect to a standard server, the Echo server, and communicate with it via a socket. It then walks you through the details of a complete client/server example, which shows you how to implement both the client side and the server side of a client/server pair.

All About Datagrams takes you step by step through a simple client/server example that uses datagrams to communicate. It then challenges you to rewrite the example using multicast socket instead.

Programmatic Access to Network Parameters explains why you might want to access network interface parameters and how to do so. It gives examples of how to list all the IP addresses assigned to the machine as well as other useful information such as whether the interface is running.

Working With Cookies discusses how cookies are used to create a session between a client and server, and how you can take advantage of cookies in your HTTP URL connections.