Web Browsers

Web Browser: 
As pointed out earlier, the Internet is a vast sea of information represented in many formats and stored on many computers. A large portion of the Internet is organized as the World Wide Web which uses hypertext. Web browsers are used to navigate through the information found on the net. They allow us to retrieve the information spread across the Internet and display it using the hypertext markup language (I-ITML). Examples of Web browsers, among others, include:

• Hot Java

• Netscape Navigator

• Internet Explorer

Java And World Wide Web

Java And Web:

World Wide Web (\\*WW) is an open-ended information retrieval system designed to be used in the Internet's distributed environment. This system contains what are known as Web pages that provide both information and controls. Unlike a menu-driven system where we are guided

through a particular direction using a decision tree structure, the Web system is open-ended and we can navigate to a new document in any direction as shown in Fig. . This is made possible with the help of a language called Hypertext Markup Language (HTML). Web pages contain HTML tags that enable us to find, retrieve, manipulate and display documents worIchvide.
Java was meant to be used in distributed environments such as Internet. Since, both the Web and Java share the same philosophy, Java could be easily incorporated into the Web system. Before Java, the World Wide Web was limited to the display of still images and texts. However, the incorporation ofJava into Web pages has made it capable of supporting animation. graphics, games, and a wide range of special effects. With the support of Java, the Web has become more interactive and dynamic. On the other hand, with the support of Web, we can run a Java program on someone else's computer across the Internet.

Java communicates with a Web page through a special tag called <APPLET>. Figure  illustrates this process. The figure shows the following communication steps:
1. The user sends a request for an HTML document to the remote computer's Web server. The Web server is a program that accepts a request, processes the request, and sends the required document.
2. The HTNIL document is returned to the user's browser. The document contains the APPLET tag, which identifies the applet.
3. The corresponding applet bytecode is transferred to the user's computer. This bytecode had been previously created by the Java compiler using the Java source code file for that applet.
4. The Java-enabled browser on the user's computer interprets the bytecodes and provides output.
5. The user may have further interaction with the applet but with no further downloading from the provider's Web server. This is because the bytecode contains all the information necessary to interpret the applet.

Java And Internet

Java And Internet:
Java is strongly associated with the Internet because of the fact that the first application program written in Java was HotJava. a Web browser to run applets on Internet. Internet users can use Jas -a to create applet programs and run them locally using a "Jas -a-enabled browser'. such as HotJava. They can also use a Java-enabled browser to download an applet located on a computer any, there in the Internet and run it on his local computer . In fact, Java applets have made the Internet a true extension of the storage system of the local computer.
Internet users can also set up their Web sites containing Java applets that could be used by other remote users of Internet. The ability of Java applets to hitch a ride on the Information Superhighway has made Java a unique programming language for the Internet. In fact, due to this, Java is popularly known as Internet language.

Java Differ From C And C++

Although java was modeled after C and C++ languages, it differ from C and C++ in many ways, java does not incorporate a number of features available in C and C++. For the benefit of C and C+ + programmers, we point out here a few major differences between C/C+ + and Java languages.

Java and C

Java is a lot like C but the major difference between Java and C is that Java is an object-oriented language and has mechanism to define classes and objects. In an effort to builds simple and safe language. the Java team did not include some of the C features in Java.
• Java does not include the C unique statement keywords goto, sizeof, and typedef.
• Java does not contain the data types struct, union and enum.
• Java does not define the type modifiers keywords auto, extern, register, signed, and unsigned.
• Java does not support an explicit pointer type.
• Java does not have a preprocessor and therefore we cannot use # define, # include, and # ifdef statements.
• Java does not support any mechanism for defining variable arguments to functions.
• Java requires that the functions with no arguments must be declared with empty parenthesis and not with the void keyword as done in C.
• Java adds new operators such as instanceof and > > >.
• Java adds labelled break and continue statements.
• Java adds many features required for object-oriented programming.

Java and C+ +

Java is a true object-oriented language while C+ + is basically C with object-oriented extension. That is what exactly the increment operator ++ indicates. C++ has maintained backward compatibility with C. It is therefore possible to write an old style C program and run it successfully under C+ +. Java appears to be similar to C+ + when we consider only the "extension" part of C+ +. However, some object-oriented features of C++ make the C++ code extremely difficult to follow and maintain.
Listed below are some major C+ + features that were intentionally omitted from Java or significantly modified.
• Java does not support operator overloading.
• Java does not have template classes as in C+ +.
• Java does not support multiple inheritance of classes. This is accomplished using a new feature called -interface".
• Java does not support global variables. Every variable and method is declared within a class and forms part of that class.
• Java does not use pointers.
• Java has replaced the destructor function with a finalize( ) function.
• There are no header files in Java.

Java also adds some new features. While C+ + is a superset of C. Java is neither a superset nor a subset of C or C++. Java may be considered as a first cousin of C++ and a second cousin of C as illustrated in Fig.. A more detailed discussion on the differences between C+ + and Java is available in Appendix C.