Java compiler: Difference between revisions

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

In [[computing]], aA '''Java compiler''' is a [[computer programcompiler]] that translates programs infor the [[Java (programming language)|Java programming language]]. [[source code]] to [[Class (file format)|Java class files]].

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>

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

* [[Javac]], included in [[Java Development Kit|JDK]] from [[Sun Microsystems]].

* [[Jikes]], an [[open source]] compiler from [[IBM]], which is written in [[C++]] and uses a variant of [[static single assignment form]] for optimization.

* [[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.

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 compiler compiles the Java source code to a Java class file that contains the generated [[Java bytecode]]. The [[Java Virtual Machine]] (JVM) loads the class file 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]]. Most Java compilers, Jikes being the only exception, do virtually no [[Optimization (computer science)|optimization]], leaving this until [[runtime]] to be done by the [[JRE]]. Even though each compiler uses a different technique, they all generate the same class file format.

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 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>

== External links ==

== See also ==

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

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

* [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

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

* [http://java.sun.com/ Java Sun]

==References==

[[Category:Java platform|Compiler]]

{{reflist}}

[[Category:Java programming language]]

== 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.

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