Jikes is an open source Java compiler from IBM that adheres strictly to the Java specification and promises an "extremely fast" compilation. Although Sun Microsystems, the inventor of Java, offers its own proprietary compiler, IBM's compiler uses the open source idea, meaning that anyone can acquire IBM's Jikes source code for free and redistribute it with modifications (if these adhere to the Java specifications). Jikes is included as part of several different variations of Linux, including the popular version from Red Hat.
IBM says that Jikes adheres to both the Java Language Specification and the Java Virtual Machine Specification, and does not support subsets, supersets, or other variations of the language. In addition to fast compilation, Jikes analyzes source code that is being compiled for dependencies on other source code files that may be needed. Jikes is available for most major operating system platforms. IBM points out that Jikes is not a Java development environment, but just a Java compiler.