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You already know how to program Java, so you'll already know about some of these things, but I want to give you an overview of what you'll find in Java 6. Just like with the previous versions of Java, the principle software product is the Java Standard Edition, also known as the Java SE. It's made up of two parts; the runtime environment is known as the JRE. It includes the libraries of executable code. These are the classes that make up the runtime libraries, and the Java Virtual Machine. Everything, in fact, that you need to run a Java program. These things are what makes Java so portable. The Java Development Kit, known as the JDK, is the compiler and debugger that can be used to develop Java programs. Actually, the JDK includes the JRE, so there is no real difference between the JDK and the SE. You'll see the names used almost interchangeably in the Sun documentation on their website, so don't let that throw you. The Java Virtual Machine is a program. There are versions of it that run on different computers, such as Apple, UNIX and Windows. The JVM, or VM if you prefer, executes compiled Java byte code so the programs are all completely portable. The JVM from Sun is also called HotSpot and it has two faces. The client VM is for platforms typically used for client applications. This version of the VM starts more quickly and uses less memory than the other. The server uses more memory but executes faster. Other than the optimizations for size or speed, the two JVMs do exactly the same thing. You can specify which JVM you want to run whenever you start the program. You can specify either the client or the server on the command line. If you don't specify, the default is the client. The examples in this course are run with the default. Actually, the example programs here are so small it doesn't really make any difference. Those are the two basic tools. I'll be showing you lots of examples of using the Java compiler and I'll be showing you lots of examples using the JVM to run programs. But there are some other tools that you need to know about. You need to at least be aware of their existence so that you'll know what you have available to you if you want to use them. This program has been around since the first days of Java. It reads the source code and uses the code and the comments it finds to generate documentation. It does an amazingly good job. The documentation that you'll be using to figure out how to apply the Java system libraries was generated using Javadoc. The really neat thing about doing it this way is that you can be sure the documentation matches the actual code. When you make a change to the code, the documentation keeps up. This is sort of a special-purpose web browser that's used in the development of Java applets. It will read the HTML of a web page and execute any Java applets found in it. If the applet viewer executes an applet successfully, any Java-enabled web browser will be able to execute it also, so you don't need to test a bunch of browsers. The jar utility can be used to create and maintain jar files, which are the files which contain libraries of executable Java code and also data files of various types, including image and audio. The files are compressed to save space and you can digitally sign them if you need to. jdb is a command-line debugger with a simple interface. There are several ways to use it, but the simplest is probably to type j-d-b on the command line to run your Java program, the same way that you would use a regular JVM. You can write native functions in C and call them from your Java program. The Java h utility reads the code of Java classes and generates C code that can be used to build the interface. Java p is a decompiler. It doesn't return the class file to its original source code, but it does extract the essentials; the class names and the method names and it can display the byte code that makes up the executable portion of the class. Extcheck has to do with installing extensions to the versions of Java you have installed on your machine. Any new extension you intend to add will be checked against any extensions that you may have already installed to make sure you get the latest version. And that's not all. I counted 25 more programs listed under tools and utilities and eight more experimental. If there is something you need, check with the Java 6 documentation because it probably exists. One of the fundamental characteristics of Java is that it is portable. You compile your program as a collection of class files and your compiled program will run on any of the several platforms. It will run on any computer that has a Java Runtime Environment installed. Sun provides a JRE for its Solaris operating system, as well as for Linux and Windows. Other companies provide Java Runtime Environments. You'll find them on Macintosh and AIX and many others, including cell phones and DVD players and so on. Java is everywhere.