Java Applets

 Why Applets? 

Applet (from the word Application) is a cute little application which runs under a parent program.   

Java is a programming language, by Sun Microsystems, and influenced heavily by C/C++.  Java is an attempt to make cross-platform computing easier/more functional.  

The idea is summed up with the phrase 'Write Once, Run Anywhere', though in practice this turns out to be a little more complex than it sounds.   

The VM

In order to run Java, you must install the Java Runtime Environment, or Virtual Machine (which is essentially a computer program which pretends to be a whole computer).  The Java VM must be written for each individual operating system, but then any OS which has a Java VM going can run a Java program.  

So, it's not really Write Once, Run Anywhere so much as Write Once, Run Anywhere That Has A Java VM.  

Applets in your Browser

This article is in the Web Development section because of the capability to embed a Java applet into a web page.  When you go to a page with an embedded applet (and you have the environment to run it), the code from the applet is downloaded into your computer and then executed on the VM.  

This allows programmers to include programs inside their web pages.  

Security

To help make this practice more secure, the Java VM imposes a set of rules to help prohibit programs from executing malicous code, but as a proprietary platform, you basically have to trust that Sun knows what it is doing when providing the security rules.  Cool stuff, but use with caution, yeah?  

Versus Flash

Adobe Flash (formerly Macromedia Flash) has been giving Java a run for its money in recent years (at least in the area of embedded applets in web pages).  

Flash tends to be lighter and faster loading than Java.  

Conversely, Java has many uses outside of webpages (which go beyond the scope of this article).