A Java compiler is a compiler for the Java programming language. The most common form of output from a Java compiler is Java class files containing platform-neutral Java bytecode. There exist also compilers emitting optimized native machine code for a particular hardware/operating system combination.

Most Java-to-bytecode compilers, Jikes being a well known exception, do virtually no optimization, leaving this until run time to be done by the JRE^{[citation needed]}.

The Java Virtual Machine (JVM) loads the class files and either interprets the bytecode or just-in-time compiles it to machine code and then possibly optimizes it using dynamic compilation.

The very first Java compiler developed by Sun Microsystems was written in C using some libraries from C++.^{[citation needed]}

A standard on how to interact with Java compilers programmatically was specified in JSR 199.

Major Java compilers

As of 2010, the following are major Java compilers:^{[citation needed]}

• javac, included in JDK from Sun Microsystems, open-sourced since 13 November 2006.
• GNU Compiler for Java, a part of the GNU Compiler Collection, which compiles C, Fortran, Pascal and other programming languages besides Java. It can also generate native code using the back-end of GCC.
• ECJ, the Eclipse Compiler for Java, is an open source incremental compiler used by the Eclipse project.

How to compile and run Java in terminal (mac) or windows

Open terminal or command prompt to get to the directory you are working in. So if your folder is C:\desktop\testJAVA you need to be in this folder to use the commands, not in e.g. C:\ folder only.

To get to the directory use cd command. e.g.

cd desktop cd foldername

To compile the Java file type in

javac filename.java

This produces a class file

To run this class file type java followed by the filename without the extension of .class

e.g. java filename

Java decompilers

A Java decompiler tries to reverse the process of compiling, that is it tries to decompile Java bytecode files (*.class) back to Java source files (*.java).

• DJ Java Decompiler [1] (Uses JAD) 10 use trial version
• JAD, written in C++, free for non-commercial use.
• JD [2], younger project, includes GUI, optional Eclipse-plugin.
• JODE, decompiler and optimizer, open-source.
• Mocha, one of the first decompilers for Java.
• AndroChef Java Decompiler [3] 10 use trial version

External links

• Sun's OpenJDK javac page
• JSR 199 Java Compiler API Java Specification Request for invoking the Java compiler from a Java program
• A Formal Introduction to the Compilation of Java, Stephan Diehl, "Software - Practice and Experience", Vol. 28(3), pages 297-327, March 1998.