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{{Short description|Program compiler for Java programming language}}

A '''Java compiler''' is a [[compiler]] for the [[Java (programming language)|Java programming language]]. The most common form of output from a Java compiler are [[Class (file format)|Java class files]] containing platform-neutral [[Java bytecode]]. There exist also compilers emitting optimized [[Machine code|native machine code]] for a particular hardware/[[operating system]] combination.

A '''Java compiler''' is a [[compiler]] for the [[Java (programming language)|Java programming language]].

Some Java compilers output optimized [[machine code]] for a particular hardware/[[operating system]] combination, called a ''[[Computing platform|___domain specific]]'' ''[[computer system]]''. An example would be the now discontinued [[GNU Compiler for Java]].<ref>{{Cite web|title=GCJ - past, present, and future|url=https://lwn.net/Articles/130796/|access-date=2021-09-24|language=en|archive-date=2019-08-02|archive-url=https://web.archive.org/web/20190802072307/https://lwn.net/Articles/130796/|url-status=live}}</ref>

Most Java-to-bytecode compilers, [[Jikes]] being a well known exception, do virtually no [[Optimization (computer science)|optimization]], leaving this until [[Run time (computing)|runtime]] to be done by the [[JRE]]{{Fact|date=April 2007}}.

The most common form of output from a Java compiler is [[Java class file]]s containing [[cross-platform]] [[intermediate representation]] (IR), called [[Java bytecode]].<ref>{{Cite web|title=The Java Virtual Machine Specification, Java SE 8 Edition, Section 1.2|url=https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-1.html#jvms-1.2|access-date=2021-09-24|language=en|archive-date=2021-09-24|archive-url=https://web.archive.org/web/20210924135604/https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-1.html#jvms-1.2|url-status=live}}</ref>

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

The [[Java Virtualvirtual Machinemachine]] (JVM) loads the class files and either [[interpreter (computing)|interprets]] the [[bytecode]] or [[just-in-time compilation|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++.{{Fact|date=February 2007}}

A standard on how to interact with Java compilers was specified in [[Java Specification Request|JSR]] 199.<ref>{{Cite web|url=https://jcp.org/en/jsr/detail?id=199|title=JSR 199: JavaTM Compiler API|access-date=2021-09-24|archive-date=2021-09-24|archive-url=https://web.archive.org/web/20210924135603/https://jcp.org/en/jsr/detail?id=199|url-status=live}}</ref>

== Major Java compilers ==

== See also ==

As of 2006, the following are major Java [[compiler]]s:

* [[List_of_compilers#Java_compilers|List of Java Compilers]]

* [[javac]], the standard Java compiler in Oracle's [[Java_Development_Kit|JDK]]

* [[javac]], included in [[Java Development Kit|JDK]] from [[Sun Microsystems]], open-sourced since 13 November 2006.

* [[GCJ]], a part of [[GNU Compiler Collection|gcc]] which compiles [[C (programming language)|C]], [[Fortran]], [[Pascal programming language|Pascal]] and other [[programming language]]s 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 (software)|Eclipse]] JDT.

* [[Jikes]], an [[open source]] compiler from [[IBM]], which is written in [[C++]] and uses a variant of [[static single assignment form]] for optimization. As of early 2007 the project is no longer being actively developed <ref>The last 1.22 version is of October 2004 [http://sourceforge.net/project/showfiles.php?group_id=128803]. The project CVS activity for the last 12 months is null [http://sourceforge.net/project/stats/detail.php?group_id=128803&ugn=jikes&type=cvs&mode=12months]</ref>.

* [[Excelsior JET]] (commercial) also compiles Java to Windows and Linux binary executables and packages them for deployment.

* [[Xcode]], developed by [[Apple Inc.]] and the primary [[Integrated development environment|IDE]] for [[Macintosh]].

== 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]] [http://www.neshkov.com/] 10 use trial version

* [[JAD (JAva Decompiler)|JAD]], written in [[C++]], free for non-commercial use.

* [[JD Java Decompiler|JD]] [http://java.decompiler.free.fr/], younger project, includes GUI, optional Eclipse-plugin.

* [[JODE]] [http://jode.sourceforge.net/], decompiler and optimizer, open-source.

==References==

{{reflist}}

{{refs}}

==External links==

* [http://openjdk.java.net/groups/compiler/ Sun's OpenJDK javac page]

* Stephan Diehl, [http://people.cis.ksu.edu/~hatcliff/605/XC/java-comp.pdf.gz "A Formal Introduction to the Compilation of Java"], ''Software - Practice and Experience'', Vol. '''28'''(3), pages 297-327, March 1998.

* [http://jikes.sourceforge.net/ Jikes homepage]

* [http://www.jcp.org/en/jsr/detail?id=199 JSR 199] Java Compiler API [[Java Specification Request]] for invoking the Java compiler from a Java program

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