Intro A

Programming languages on the web come and go. Stay tuned for the next language. Java seems to be destined to stay for awhile. Created by Sun Microsystems, it is a programming language similar to C++, one of today's most used languages in the industry. It is especially valuable for the Web, however, because it is platform independent. It will run the same on a Windows machine as it will on Macintosh, Sun, or Linux operating system. Another great feature of Java is that it is downloaded to the clients machine and uses the processor on that machine rather than Internet bandwidth.

Java is mainly used for 3 categories of programs: applications, servlets, and applets. Applications are stand alone programs that are often large and complex. They are created for a given need within a given industry. For example, you could use Java(or most other languages) to create a program for the banking industry that ran their ATMS. You could create a computer game to sell to high school kids who should be working on their homework :). By creating your application with Java, theoretically, you could create one program that would run on any computer operating system because Java has an "interpreter" that converts the code to each machines operating system language. Servlets are relatively new and remain on a webserver and serve out data to users. Applets are the most common Java useage form. They reside on a webserver like an html document and are downloaded to the user's machine and run inside the browser. Applet means "small application". They are easier(not easy) to write and are the only of the 3 Java uses we will be creating in this class.

Java was made popular when Netscape 2.0 added a machine language(1's and 0's) interpreter in 1995. This allowed the browser to read the compiled machine language of a Java applet. The Java applet(small application written to be executed within an web document) is downloaded with the HTML document and tagged in the HTML to run at the appropriate time. Java is an object-oriented language, meaning that everything, including text is defined as an object and given properties (data) and functions(methods). Java also organizes objects into classes to simplify the programming. Java, is however, anything but simple compared to what you have learned in the first 2 trimesters of this class.

If you're interested in learning Java, the first thing you should do is visit the Java home page at Sun Microsystems and download the Java Developer's Kit (JDK) and the documentation that goes with it. It's important to download the version that matches the operating system on which you'll be doing your development. But once it's compiled, an applet built with the JDK will run on any system for which a Java browser is available. And, of course, here's the "not a plug" again. PeachPit Press has a Java Visual Quick Start Guide. Java is a difficult enough language that the QuickStart Guide will only just get you started. It is the text we are going to be using this trimester. Your book was written for Java1 which corresponds to JDK 1.0 and it's revisions. What is now called Java2 uses more add on classes and corresponds to JDK 1.2. There is even a JDK 1.3. Newer browsers can run Java2 but as always with web development, we need to be sure our code works with all or almost all users. It is safer for now to stick with Java1 code so all users can see your work. And, as browser versions evolve, web builders will upgrade to Java2 and beyond in the future.

There are also tons of sites giving away free Java applets that you can download and insert into your webpage. Of course, our goal will be to write original applets, but you can learn a lot by looking at others' work. Some of these applets provide the source code needed to make modifications. Others do not. Most all are quite user friendly in allowing you to modify the html that starts the applet running in your user's browser. Try these sites for free Java applets:
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