• Unlike most programming languages, Java source code is not compiled into native code. Instead, a Java compiler translates Java source code into an architecturally-neutral intermediate form known as bytecode.
• Instructions in this bytecode are interpreted by a Java interpreter.
• Sun provide a Software Development Kit for the Java 2 Platform (Java 2 SDK). This includes a compiler and an interpreter. Previous versions of the SDK were known as the Java Development Kit (JDK).
• The Java 2 SDK was first released in December 1998. The latest version is 1.4.2. However, some people still use versions of the JDK such as JDK 1.1.x and JDK 1.0.2 (which dates back to 1996). Whereever possible, new systems should be written using the latest version of the Java 2 SDK.
• Sun provide implementations of the Java 2 SDK for Solaris 2.x, for Windows and for Linux. All of these products can be downloaded (free of charge) from: http://java.sun.com/products/.
• Other companies provide rival products to Sun's SDK.
• Programs written for an early version of Java can be compiled by a more recent compiler. Bytecodes produced by an old compiler can be interpreted by a more recent interpreter.