Java Applets and the Internet Core Java

The idea here is simple: Users will download Java bytecodes from the Internet and run them on their own machines. Java programs that work on web pages are called applets. To use an applet, you only need a Java-enabled web browser, which will execute the bytecodes for you. You need not install any software. Because Sun licenses the Java source code and insists that there be no changes in the language and standard library, a Java applet should run on any browser that is advertised as Java-enabled. You get thelatest version of the program whenever you visit the web page containing the applet.

Most important, thanks to the security of the virtual machine, you need never worry about attacks from hostile code.

When the user downloads an applet, it works much like embedding an image in a webpage. The applet becomes a part of the page, and the text flows around the space usedfor the applet. The point is, the image is alive. It reacts to user commands, changes its appearance, and sends data between the computer presenting the applet and the computer serving it.

a good example of a dynamic web page that carries out sophisticated calculations. The Jmol applet displays molecular structures. By using the mouse, you can rotate and zoom each molecule to better understand its structure. This kind of direct manipulation is not achievable with static web pages, but applets make it possible.

The Jmol applet

The Jmol applet

When applets first appeared, they created a huge amount of excitement. Many people believe that the lure of applets was responsible for the astonishing popularity of Java. However, the initial excitement soon turned into frustration. Various versions of Netscape and Internet Explorer ran different versions of Java, some of which were seriously outdated. This sorry situation made it increasingly difficult to develop applets that took advantage of the most current Java version. Today, most web pages simply use JavaScript or Flash when dynamic effects are desired in the browser. Java, on the other hand, has become the most popular language for developing the server-side applications that produce web pages and carry out the backend logic.

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Core Java Topics