What is meant by cookies ? Explain ?

A Cookie is a small bit of textual information send by an website to the browser with some information about the user. The browser sends it back to the webserver upon subsequent visits of the user to that particular website.

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Can we send object using Sockets ?

Sure. Why not? Socket I/O is exposed at streams. We can send/receive objects to/from streams using serialization.


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What is difference in between Java Class and Bean ?

A Bean can have associated support classes: a BeanInfo class providing information about the bean, its properties and its events, and also property editors and a graphical customizer.

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What is bean ? Where it can be used ?

A JavaBean is basically a Java class which satisfies a few simple rules (it must have a no-arg constructor, properties have getters and setters; actually, you can get around the last rule by supplying a BeanInfo object for your bean). JavaBeans were originally conceived for graphical application builder tools, but that emphasis has shifted considerably and they're now used almost everywhere.

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Where the CardLayout is used ?

CardLayout manages two or more components that share the same display space. It lets you use one container (usually a panel) to display one out of many possible component children (like flipping cards on a table). A program can use this layout to show a different child component to different users. For example, the interface shown to an administrator might have additional functionality from the interface shown to a regular user. With card layout, our program can show the appropriate interface depending on the type of user using the program. Another typical use of card layout would be to let end user toggle among different displays and choose the one they prefer. In this case, the program must provide a GUI for the user to make the selection.

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What are 4 drivers available in JDBC ?

Type 1: JDBC-ODBC Bridge
The type 1 driver, JDBC-ODBC Bridge, translates all JDBC calls into ODBC (Open DataBase Connectivity) calls and sends them to the ODBC driver. As such, the ODBC driver, as well as, in many cases, the client database code, must be present on the client machine. May be used when an ODBC driver has already been installed on client machine and performance is not an issue.
Type 2: Native-API/partly Java driver
JDBC driver type 2 -- the native-API/partly Java driver -- converts JDBC calls into database-specific calls for databases such as SQL Server, Informix, Oracle, or Sybase. The type 2 driver communicates directly with the database server; therefore it requires that some binary code be present on the client machine. Can be used when application is not for internet.
Type 3: Net-protocol/all-Java driver
JDBC driver type 3 -- the net-protocol/all-Java driver -- follows a three-tiered approach whereby the JDBC database requests are passed through the network to the middle-tier server. The middle-tier server then translates the request (directly or indirectly) to the database-specific native-connectivity interface to further the request to the database server. If the middle-tier server is written in Java, it can use a type 1 or type 2 JDBC driver to do this.Type 3 drivers are best suited for environments that need to provide connectivity to a variety of DBMS servers and heterogeneous databases and that require significantly high levels of concurrently connected users where performance and scalability are major concerns.
Type 4: Native-protocol/all-Java driver
The native-protocol/all-Java driver (JDBC driver type 4) converts JDBC calls into the vendor-specific database management system (DBMS) protocol so that client applications can communicate directly with the database server. Level 4 drivers are completely implemented in Java to achieve platform independence and eliminate deployment administration issues. Useful for Internet-related applications.


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Why do you Canvas ?

The Canvas class of java.awt is used to provide custom drawing and event handling. It provides a general GUI component for drawing images and text on the screen. It does not support any drawing methods of its own, but provides access to a Graphics object through its paint() method. The paint() method is invoked upon the creation and update of a canvas so that the Graphics object associated with a Canvas object can be updated.


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What is Difference between AWT and Swing ?

Swing provides a richer set of components than AWT. They are 100% Java-based. AWT on the other hand was developed with the mind set that if a component or capability of a component weren’t available on one platform, it wouldn’t be available on any platform. Due to the peer-based nature of AWT, what might work on one implementation might not work on another, as the peer-integration might not be as robust. There are a few other advantages to Swing over AWT:


Swing provides both additional components and added functionality to AWT-replacement components
Swing components can change their appearance based on the current "look and feel" library that's being used.
Swing components follow the Model-View-Controller (MVC) paradigm, and thus can provide a much more flexible UI.
Swing provides "extras" for components, such as:
Icons on many components
Decorative borders for components
Tool tips for components
Swing components are lightweight (less resource intensive than AWT)
Swing provides built-in double buffering
Swing provides paint debugging support for when you build your own components

Swing also has a few disadvantages:


It requires Java 2 or a separate JAR file
If you're not very careful when programming, it can be slower than AWT (all components are drawn)
Swing components that look like native components might not act exactly like native components.



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What is JFC ?

Java Foundation Classes include:


Standard AWT 1.1
Accessibility interface
Lightweight components: which are user interface components that do not subclass an existing AWT interface element. They do not use native interface elements as provided by the underlying windowing system. This means that they are less limiting than standard AWT components.
Java look and feel
Support for native look and feel
Services such as Java2D and Drag and Drop.


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What is the base class for all swing components ?

JComponent (except top-level containers)

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What is JNI ?

JNI is an acronym of Java Native Interface. Using JNI we can call functions which are written in other languages from Java. Following are its advantages and disadvantages:
Advantages:


You want to use your existing library which was previously written in other language.
You want to call Windows API function.
For the sake of execution speed.
You want to call API function of some server product which is in c or c++ from java client.

Disadvantages:

You can’t say write once run anywhere.
Difficult to debug runtime error in native code.
Potential security risk.
You can’t call it from Applet.


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What is JAR file ?

JavaARchive files are a big glob of Java classes, images, audio, etc., compressed to make one simple, smaller file to ease Applet downloading. Normally when a browser encounters an applet, it goes and downloads all the files, images, audio, used by the Applet separately. This can lead to slower downloads.


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What are statements in JAVA ?

Statements are equivalent to sentences in natural languages. A statement forms a complete unit of execution. The following types of expressions can be made into a statement by terminating the expression with a semicolon ( :


Assignment expressions
Any use of ++ or --
Method calls
Object creation expressions

These kinds of statements are called expression statements.
In addition to these kinds of expression statements, there are two other kinds of statements. A declaration statement declares a variable. A control flow statement regulates the order in which statements get executed. The for loop and the if statement are both examples of control flow statements.


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When is update method called ?

Whenever a screen needs redrawing (e.g., upon creation, resizing, validating) the update method is called. By default, the update method clears the screen and then calls the paint method, which normally contains all the drawing code.


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What is the order of method invocation in an Applet ?

public void init() : Initialization method called once by browser.
public void start() : Method called after init() and contains code to start processing. If the user leaves the page and returns without killing the current browser session, the start () method is called without being preceded by init ().
public void stop() : Stops all processing started by start (). Done if user moves off page.
public void destroy() : Called if current browser session is being terminated. Frees all resources used by applet.


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How will you initialize an Applet ?

Write my initialization code in the applets init method or applet constructor.



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What is the use of Servlets ?

Servlets may be used at different levels on a distributed framework. The following are some examples of servlet usage:


To accept form input and generate HTML Web pages dynamically.
As part of middle tiers in enterprise networks by connecting to SQL databases via JDBC.
In conjunction with applets to provide a high degree of interactivity and dynamic Web content generation.
For collaborative applications such as online conferencing.
A community of servlets could act as active agents which share data with each other.
Servlets could be used for balancing load among servers which mirror the same content.
Protocol support is one of the most viable uses for servlets. For example, a file service can start with NFS and move on to as many protocols as desired; the transfer between the protocols would be made transparent by servlets. Servlets could be used for tunneling over HTTP to provide chat, newsgroup or other file server functions.


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How do you communicate in between Applets & Servlets ?

We can use the java.net.URLConnection and java.net.URL classes to open a standard HTTP connection and "tunnel" to the web server. The server then passes this information to the servlet in the normal way. Basically, the applet pretends to be a web browser, and the servlet doesn't know the difference. As far as the servlet is concerned, the applet is just another HTTP client.


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Explain RMI Architecture?

RMI uses a layered architecture, each of the layers could be enhanced or replaced without affecting the rest of the system. The details of layers can be summarised as follows:


Application Layer: The client and server program
Stub & Skeleton Layer: Intercepts method calls made by the client/redirects these calls to a remote RMI service.
Remote Reference Layer: Understands how to interpret and manage references made from clients to the remote service objects.
Transport layer: Based on TCP/IP connections between machines in a network. It provides basic connectivity, as well as some firewall penetration strategies.

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What is the difference between C++ & Java?

Well as Bjarne Stroustrup says "..despite the syntactic similarities, C++ and Java are very different languages. In many ways, Java seems closer to Smalltalk than to C++..". Here are few I discovered:


Java is multithreaded
Java has no pointers
Java has automatic memory management (garbage collection)
Java is platform independent (Stroustrup may differ by saying "Java is a platform" )
Java has built-in support for comment documentation
Java has no operator overloading
Java doesn’t provide multiple inheritance
There are no destructors in Java.



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What do you know about the garbage collector?

Garbage collector is a runtime component of Java which sits on top of the heap: memory area from which Java objects are created and periodically scans it for objects which are eligible to be reclaimed when there are no references to these objects in the program. There is simply no way to force garbage collection, but you can suggest your intention of getting the object garbage collecetd to Java Virtual Machine by calling

code:
--------------------------------------------------------------------------------

System.gc().





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