Java is a full-featured programming language like C/C++, but simpler and more tightly structured. Like C++, Java is an object-oriented programming language, which is a concept I’ll expand on in the next article in this series. In basic terms, however, Java programs are written by creating a structured set of software components that interact with each other to produce the desired effect. These components are called objects, and the fundamental task of a Java developer is to determine the best object structure to achieve a system that works as required, as efficiently as possible and, wherever possible, producing components that may be reused in similar applications.
If all that sounds a little scary, don't worry; it'll all make sense once you've learned it. For now, we'll proceed in baby steps.
Java programs, instead of running directly on a computer's operating system, run on a "Java Virtual Machine" (JVM), which itself is a program that runs on the computer's operating system. Since the production of Java Virtual Machines is highly standardized, incompatibilities between different platforms are minimal. This means that, in theory, any operating system that has a JVM (pretty much all major operating systems these days) can run any Java program, with no need to recompile the program for each platform. This leads to one of the most attractive features of the Java language: "Write Once, Run Anywhere" (WORA). The disadvantage is that Java programs tend to run slower because the Virtual Machine has to convert Java program instructions and pass them to the operating system on which it is running.
Most current Web browsers can also run Java programs that are downloaded from the Web, either using a JVM built into the browser (as in Netscape 4 and Internet Explorer browsers), or by interfacing with a standard JVM installed separately (as in Netscape 6 and Opera browsers). Java programs designed to run in Web browsers are called Java Applets. When Java was originally released, much of the marketing hype surrounding the language centred on these little programs that run in Web browsers. Over the years, however, the focus of Java on the Web has shifted to server-side applications (including Servlets and JSP), and Java applets have been replaced in many instances by more nimble technologies like Dynamic HTML Flash. Common uses of Java applets these days include Web-based chat programs and online games.
Now that you know what you’re getting yourself into, it’s time for you to get a hold of the tools you’ll need to get started with your Java development efforts.
