What Is Java?

In discussing Java, it is important to distinguish between the Java programming language, the Java Virtual Machine, and the Java platform. The Java programming language is the language in which Java applications, applets, servlets, and components are written. When a Java program is compiled, it is converted to byte codes that are the portable machine language of a CPU architecture known as the Java Virtual Machine (also called the Java VM or JVM). The JVM can be implemented directly in hardware, but it is usually implemented in the form of a software program that interprets and executes byte codes.

The Java Programming Language

The Java programming language is a state-of-the-art, object-oriented language that has a syntax similar to that of C. The language designers strove to make the Java language powerful, but, at the same time, they tried to avoid the overly complex features that have bogged down other object-oriented languages like C++. By keeping the language simple, the designers also made it easier for programmers to write robust, bug-free code. As a result of its elegant design and next-generation features, the Java language has proved popular with programmers, who typically find it a pleasure to work with Java after struggling with more difficult, less powerful languages.

Java 5.0, includes a number of new language features, most notably generic types, which increase both the complexity and the power of the language. Most experienced Java programmers have welcomed the new features, despite the added complexity they bring.
Java 6.0 Beta the latest version of the Java language,

 The Java Virtual Machine

The Java Virtual Machine, or Java interpreter, is the crucial piece of every Java installation. By design, Java programs are portable, but they are only portable to platforms to which a Java interpreter has been ported. Sun ships VM implementations for its own Solaris operating system and for Microsoft Windows and Linux platforms. Many other vendors, including Apple and various commercial Unix vendors, provide Java interpreters for their platforms. The Java VM is not only for desktop systems, however. It has been ported to set-top boxes and handheld devices that run Windows CE and PalmOS.

Although interpreters are not typically considered high-performance systems, Java VM performance has improved dramatically since the first versions of the language. The latest releases of Java run remarkably fast. Of particular note is a VM technology called just-in-time (JIT) compilation whereby Java byte codes are converted on the fly into native platform machine language, boosting execution speed for code that is run repeatedly

The Java Platform

The Java platform is just as important as the Java programming language and the Java Virtual Machine. All programs written in the Java language rely on the set of predefined classes[2] that comprise the Java platform. Java classes are organized into related groups known as packages. The Java platform defines packages for functionality such as input/output, networking, graphics, user-interface creation, security, and much more.