A platform is the hardware or software environment in which a program runs. We've already mentioned some of the most popular platforms like Microsoft Windows, Linux, Solaris OS, and Mac OS. Most platforms can be described as a combination of the operating system and underlying hardware. The Java platform differs from most other platforms in that it's a software-only platform that runs on top of other hardware-based platforms.

Java is an object-oriented programming language. But what are objects? An object is a self-contained entity which has its own private collection of properties (ie. data) and methods (ie. operations) that encapsulate functionality into a reusable and dynamically loaded structure. After a class definition has been created as a prototype, it can be used as a template for creating new classes that add functionality. Objects are programing units of a particular class. Dynamic loading implies that applications can request new objects of a particular class to be supplied on an 'as needed' basis. Objects provide the extremely useful benefit of reusable code that minimizes development time.

In the formula in Figure 1, pi is a named constant whose value is shown.  Constants in programming mean pretty much the same thing that they mean in algebraic formulas. That is, the value of a constant never changes.
The terms a and r in the formula in Figure 1 are variables.  Going further, your algebra teacher may have told you that a is the dependent variable while r is an independent variable. That is to say, the value of the area is dependent on the value that you assign to the radius before you calculate the area.
Variables also mean pretty much the same thing in programming that they mean in algebraic formulas.  Every variable has a name (such as a or r) and the value of the variable can change.  In programming, this means that the value can change as the program executes over time.

The Windows X86 release is a self extracting archive. You will need about six megabytes of free disk space to install the JDK. Execute the file by double-clicking on it in the File Manager or by selecting Run... from the Program Manager's File menu and typing the path to the file. This will unpack the archive. The full path is unimportant, but for simplicity's sake I am going to assume you installed it from the root of your C: drive. If this is the case the files will live in C:\java. If you unpacked it somewhere else just replace C:\ by the full path to the java directory in what follows.

If you're on a shared system at a university or an Internet service provider, there's a good chance Java is already installed. Ask your local support staff how to access it. Otherwise follow these instructions.
The Unix release is a compressed tar file. You will need about nine megabytes of disk space to uncompress and untar the JDK. Double that would be very helpful. You do this with the commands:
% uncompress JDK-1_0_2-solaris2-sparc.tar.Z % tar xvf JDK-1_0_2-solaris2-sparc.tar