What you need to run Java programs is:

• a compiler to translate the Java source code into byte code
• a copy of the libraries which provide, for example, GUI facilities
• an interpreter which interprets the Java byte code to execute the program

If you write a Java program, you either write an applet or an application. Therefore there are 2 types of interpreter - one type interprets applets (sometimes called an applet viewer) and the other type interprets applications.

All these facilities are often bundled up into an integrated software development environment. These usually also provide an editor and a debugger. They also often provide a browser for looking at the contents of the library.

There are a number of commercially available software development environments for Java. The major ones are:

• Borland JBuilder - go here for how to use JBuilder 5.
• Microsoft J++, but it looks like it is being phased out. Instead Microsoft are offering a language called Visual J# .NET, which seems to be Java for its .NET platform

You can often get these for free. For example, PC magazines sometimes issue a free CD that holds slightly out-of-date versions of packages.

Alternatively it may be better to use a free package:

• Sun's Java Software Development Kit (SDK) - a command line interface to the compiler and interpreter. See the Sun Microsystems web site for Java . A problem: this is a large download.
• Japa - an integrated software development environment for beginners, available free for download. This is simple, small and easy to use. It has a GUI. It is also a small download. Windows platforms only. It has been developed by Mike Parr. It works in conjunction with Sun's Java SDK (which must also be downloaded), but an older and much smaller version of the SDK is available on the Japa site. This is really good.
• Java Junction - if you still need it.
• BlueJ - is also an integrated software development environment for beginners, available free for download. This also is simple, small (about 1.3 megabytes) and easy to use. It works in conjunction with Sun's Java SDK (which must be separately downloaded) and is available for Windows, Mac OS and as a portable Java program for any machine that supports Java.

It can be difficult to keep track of the way that Sun (who maintain Java) refer to different versions of Java. The current mainstream version is called Java 2. But within that name are various releases - Java 1.2, 1.2.2 etc. Java 1.2 actually became the first version of Java 2 when Sun reckoned that Java had become sufficiently stable to relaunch it as Java 2.