Java platform

The Java™ platform is the environment for developing and managing Java applets and applications. It consists of three primary components: the Java language, the Java packages, and the Java virtual machine.

The Java language and packages are similar to C++ and its class libraries. The Java packages contain classes, which are available in any compliant Java implementation. The application programming interface (API) should be the same on any system that supports Java.

Java differs from a traditional language, like C++, in the way it compiles and runs. In a traditional programming environment, you write and compile source code of a program into object code for a specific hardware and operating system. The object code binds to other object code modules to create a running program. The code is specific for a particular set of computer hardware and does not run on other systems without being changed. This figure illustrates the traditional language deployment environment.

• Java applets and applications
  An applet is a Java program designed to be included in an HTML Web document. You can write your Java applet and include it in an HTML page, much in the same way an image is included. When you use a Java-enabled browser to view an HTML page that contains an applet, the applet's code is transferred to your system and is run by the browser's Java virtual machine.
• Java virtual machine
  The Java virtual machine is a runtime environment that you can add into a web browser or any operating system, such as IBM^® i5/OS™. The Java virtual machine runs instructions that a Java compiler generates. It consists of a bytecode interpreter and runtime that allow Java class files to run on any platform, regardless of the platform on which they were originally developed.
• Java JAR and class files
  A Java ARchive (JAR) file is a file format that combines many files into one. The Java environment differs from other programming environments in that the Java compiler does not generate machine code for a hardware-specific instruction set. Instead, the Java compiler converts Java source code into Java virtual machine instructions, which Java class files store. You can use JAR files to store class files. The class file does not target a specific hardware platform, but instead targets the Java virtual machine architecture.
• Java threads
  A thread is a single independent stream that runs within a program. Java is a multithreaded programming language, so more than one thread may be running within the Java virtual machine at one time. Java threads provide a way for a Java program to perform multiple tasks at the same time. A thread is essentially a flow of control in a program.
• Sun Microsystems, Inc. Java Development Kit
  The Java Development Kit (JDK) is software that is distributed by Sun Microsystems, Inc. for Java developers. It includes the Java interpreter, Java classes, and Java development tools: compiler, debugger, disassembler, appletviewer, stub file generator, and documentation generator.