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{{Infobox programming language
| name = Java
| logo = [[File:Java programming language logo.svg|259x259px]]
| paradigm = [[Programming paradigm#Multi-paradigm|Multi-paradigm]]: [[Object-oriented]] ([[Class-based programming|class-based]]), [[Structured programming|structured]], [[imperative programming|imperative]], [[Generic programming|generic]], [[Reflection (computer programming)|reflective]], [[Concurrent computing|concurrent]]
| year = {{Start date and age|1995|5|23}}<ref>{{cite web | url=https://www.forbes.com/sites/oracle/2015/05/20/javas-20-years-of-innovation/ | title=Java's 20 Years of Innovation | publisher=Forbes | date=May 20, 2015 | accessdate=March 18, 2016 | author=Binstock, Andrew}}</ref>
| designer = [[James Gosling]]
| developer = [[Sun Microsystems]] (now owned by [[Oracle Corporation]])
| typing = [[type system|Static, strong, safe]], [[Nominal type system|nominative]], [[manifest typing|manifest]]
| implementations = [[OpenJDK]], [[GNU Compiler for Java]] (GCJ), [[:Category:Java virtual machine|many others]]
| influenced_by = [[Ada (programming language)|Ada 83]], [[C++]],<ref>{{cite web | url=https://books.google.com/books?id=0rUtBAAAQBAJ&lpg=PA133&pg=PA133#v=onepage&q&f=true|title=Cracking The Java Programming Interview :: 2000+ Java Interview Que/Ans |author=Harry. H. Chaudhary |accessdate=May 29, 2016 |date=July 28, 2014}}</ref> [[C Sharp (programming language)|C#]],<ref>Java 5.0 added several new language features (the [[foreach loop|enhanced for loop]], [[Object type (object-oriented programming)#Autoboxing|autoboxing]], [[variadic function|varargs]] and [[Java annotation|annotations]]), after they were introduced in the similar (and competing) [[C Sharp (programming language)|C#]] language. [http://www.barrycornelius.com/papers/java5/] [http://www.levenez.com/lang/]</ref> [[Eiffel (programming language)|Eiffel]],<ref>{{cite web |author1=Gosling, James |author2=McGilton, Henry |title=The Java Language Environment |date=May 1996 |url=http://www.oracle.com/technetwork/java/langenv-140151.html }}</ref> [[Generic Java]], [[Mesa (programming language)|Mesa]],<ref>{{cite web |author1=Gosling, James |author2=Joy, Bill |author3=Steele, Guy |author4=Bracha, Gilad |title=The Java Language Specification, 2nd Edition |url= http://java.sun.com/docs/books/jls/second_edition/html/intro.doc.html#237601 }}</ref> [[Modula-3]],<ref>{{cite web |url=http://www.computerworld.com.au/index.php/id;1422447371;pp;3;fp;4194304;fpid;1 |title=The A-Z of Programming Languages: Modula-3 |publisher=Computerworld.com.au |accessdate=2010-06-09 }}</ref> [[Oberon (programming language)|Oberon]],<ref>[[Niklaus Wirth]] stated on a number of public occasions, e.g. in a lecture at the Polytechnic Museum, Moscow in September 2005 (several independent first-hand accounts in Russian exist, e.g. one with an audio recording: {{cite web |author=Filippova, Elena|title=Niklaus Wirth's lecture at the Polytechnic Museum in Moscow|date=September 22, 2005|url=http://www.delphikingdom.com/asp/viewitem.asp?catalogid=1155}}), that the Sun Java design team licensed the Oberon compiler sources a number of years prior to the release of Java and examined it: a (relative) compactness, type safety, garbage collection, no multiple inheritance for classes{{snd}} all these key overall design features are shared by Java and Oberon.</ref> [[Objective-C]],<ref>[[Patrick Naughton]] cites [[Objective-C]] as a strong influence on the design of the Java programming language, stating that notable direct derivatives include Java interfaces (derived from Objective-C's [[Objective-C#Protocols|protocol]]) and primitive wrapper classes. [http://cs.gmu.edu/~sean/stuff/java-objc.html]</ref> [[UCSD Pascal]],<ref>{{cite web |url=http://www.fscript.org/prof/javapassport.pdf |quote=The project went ahead under the name "green" and the language was based on an old model of [[UCSD Pascal]], which makes it possible to generate interpretive code |title=History of Java |work=Java Application Servers Report |author=TechMetrix Research |year=1999 }}</ref><ref>{{cite web |url=http://queue.acm.org/detail.cfm?id=1017013 |title=A Conversation with James Gosling – ACM Queue |publisher=Queue.acm.org |date=August 31, 2004 |accessdate=2010-06-09 }}</ref> [[Object Pascal]]<ref>In the summer of 1996, Sun was designing the precursor to what is now the event model of the AWT and the JavaBeans TM component architecture. Borland contributed greatly to this process. We looked very carefully at Delphi Object Pascal and built a working prototype of bound method references in order to understand their interaction with the Java programming language and its APIs.[https://web.archive.org/web/20120627043929/http://java.sun.com/docs/white/delegates.html White Paper About Microsoft's "Delegates"]</ref>
| influenced = [[Ada (programming language)|Ada 2005]], [[BeanShell]], [[C Sharp (programming language)|C#]], [[Chapel (programming language)|Chapel]],<ref name="chplspec">{{cite web|title=Chapel spec (Acknowledgements)|url=http://chapel.cray.com/spec/spec-0.98.pdf|date=October 1, 2015|accessdate=2016-01-14|publisher=Cray Inc}}</ref> [[Clojure]], [[ECMAScript]], [[Fantom (programming language)|Fantom]], [[Gambas]],<ref name="gambas">{{cite web | url=http://gambaswiki.org/wiki/doc/intro?nh&l=en | title=Gambas Documentation Introduction | publisher=Gambas Website| accessdate=2017-10-09}}</ref> [[Groovy (programming language)|Groovy]], [[Hack (programming language)|Hack]],<ref>{{cite web |url=http://www.infoworld.com/article/2610885/facebook-q-a--hack-brings-static-typing-to-php-world.html |title=Facebook Q&A: Hack brings static typing to PHP world |publisher=InfoWorld |date=March 26, 2014 |accessdate=2015-01-11 }}</ref> [[Haxe (programming language)|Haxe]], [[J Sharp|J#]], [[JavaScript]], [[Kotlin (programming language)|Kotlin]], [[PHP]], [[Python (programming language)|Python]], [[Scala (programming language)|Scala]], [[Seed7]], [[Vala (programming language)|Vala]]
| dialects = [[Generic Java]], [[Pizza (programming language)|Pizza]]
| license = [[GNU General Public License]], [[Java Community Process]]
| website = {{url|oracle.com/java/}}
| file_ext = .java, [[Java class file|.class]], [[JAR (file format)|.jar]]
| wikibooks = Java Programming
}}

'''Java''' is a general-purpose [[Programming language|computer programming language]] that is [[concurrent computing|concurrent]], [[Class-based programming|class-based]], [[Object-oriented programming|object-oriented]],{{sfn|Gosling|Joy|Steele|Bracha|2014|p=1}} and specifically designed to have as few implementation dependencies as possible. It is intended to let application developers "[[write once, run anywhere]]" (WORA),<ref>{{cite web
| url=http://www.computerweekly.com/Articles/2002/05/02/186793/write-once-run-anywhere.htm
| title=Write once, run anywhere?
| date=May 2, 2002
| publisher=[[Computer Weekly]]
| accessdate=2009-07-27}}</ref> meaning that [[compiler|compiled]] Java code can run on all platforms that support Java without the need for recompilation.<ref name="design_goals">{{cite web
| url=http://www.oracle.com/technetwork/java/intro-141325.html
| title=1.2 Design Goals of the Java™ Programming Language
| publisher=Oracle |date=January 1, 1999 |accessdate=2013-01-14
}}</ref> Java applications are typically compiled to [[Java bytecode|bytecode]] that can run on any [[Java virtual machine]] (JVM) regardless of [[computer architecture]]. As of 2016, Java is one of the most [[Measuring programming language popularity|popular programming languages in use]],<ref>{{cite web |url=https://www.wired.com/2013/01/java-no-longer-a-favorite/|title=Is Java Losing Its Mojo? |quote=Java is on the wane, at least according to one outfit that keeps on eye on the ever-changing world of computer programming languages. For more than a decade, it has dominated the [[TIOBE index|TIOBE]] Programming Community Index, and is back on top –  a snapshot of software developer enthusiasm that looks at things like internet search results to measure how much buzz different languages have. But lately, Java has been slipping. |first=Robert |last=McMillan |date=August 1, 2013 |publisher=[[wired.com]]}}</ref><ref>[http://redmonk.com/sogrady/2015/01/14/language-rankings-1-15/ RedMonk Index] on redmonk.com (Stephen O'Grady, January 2015)</ref><ref name="languagepopularity2013">{{cite web |url=http://www.langpop.com/ |publisher=langpop.com |title=Programming Language Popularity |accessdate=2015-04-02 |quote="Normalized Comparison: 1st C, 2nd Java, 3rd PHP" |date=October 25, 2013}}</ref><ref>{{cite web |url=http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html |title=TIOBE Programming Community Index |year=2015 |accessdate=2015-04-03 }}</ref> particularly for client-server web applications, with a reported 9 million developers.<ref>{{Cite web|url=http://www.oracle.com/technetwork/articles/java/afterglow2013-2030343.html|title=JavaOne 2013 Review: Java Takes on the Internet of Things|website=www.oracle.com|access-date=2016-06-19}}</ref> Java was originally developed by [[James Gosling]] at [[Sun Microsystems]] (which has since been [[Sun acquisition by Oracle|acquired by Oracle Corporation]]) and released in 1995 as a core component of Sun Microsystems' [[Java (software platform)|Java platform]]. The language derives much of its [[Syntax (programming languages)|syntax]] from [[C (programming language)|C]] and [[C++]], but it has fewer [[low-level programming language|low-level]] facilities than either of them.

The original and [[reference implementation]] Java [[compiler]]s, virtual machines, and [[library (computing)|class libraries]] were originally released by Sun under proprietary licenses. As of May 2007, in compliance with the specifications of the [[Java Community Process]], Sun [[Software relicensing|relicensed]] most of its Java technologies under the [[GNU General Public License]]. Others have also developed alternative implementations of these Sun technologies, such as the [[GNU Compiler for Java]] (bytecode compiler), [[GNU Classpath]] (standard libraries), and [[IcedTea]]-Web (browser plugin for applets).

The latest version is [[Java version history|Java 9]], released on September 21, 2017,<ref>{{Cite web|url=https://adtmag.com/articles/2017/09/21/java-releases.aspx|title=Java SE 9 and Java EE 8 Released Today|last=Waters|first=John K.|date=September 21, 2017|website=ADTMag|archive-url=https://web.archive.org/web/20170921233334/https://adtmag.com/articles/2017/09/21/java-releases.aspx|archive-date=September 21, 2017|dead-url=no|access-date=}}</ref> and is one of the two versions currently supported for free by Oracle. Versions earlier than Java 8 are supported by companies on a commercial basis; e.g. by Oracle back to Java 6 as of October 2017 (while they still "highly recommend that you uninstall"{{fact|date=November 2017}} pre-Java 8 from at least Windows computers).

==History==
{{See also|Java (software platform)#History}}
[[File:Duke (Java mascot) waving.svg|thumb|upright|Duke, the Java mascot]]
[[File:James Gosling 2008.jpg|thumb|[[James Gosling]], the creator of Java (2008)]]
[[File:Tiobeindex.png|thumb|The [[TIOBE index|TIOBE]] [[Measuring programming language popularity|programming language popularity index]] graph from 2002 to 2015. Over the course of a decade Java (blue) and C (black) competing for the top position.]]<!--Outdated, Java is number one since it seems May 13, 2015.-->

[[James Gosling]], Mike Sheridan, and [[Patrick Naughton]] initiated the Java language project in June 1991.<ref>{{cite web |url=http://java.sun.com/features/1998/05/birthday.html  |title=Java technology: The early years |last=Byous |first=Jon |date=c. 1998 |work=Sun Developer Network |publisher=[[Sun Microsystems]] |accessdate=2005-04-22|archiveurl=https://web.archive.org/web/20050420081440/http://java.sun.com/features/1998/05/birthday.html |archivedate=April 20, 2005}}</ref> Java was originally designed for interactive television, but it was too advanced for the digital cable television industry at the time.<ref>Object-oriented programming {{cite web |url=http://www.java.com/en/javahistory/ |title=The History of Java Technology |date=c. 1995 |work=Sun Developer Network |accessdate=2010-04-30 }}</ref> The language was initially called ''[[Oak (programming language)|Oak]]'' after an [[oak]] tree that stood outside Gosling's office. Later the project went by the name ''Green'' and was finally renamed ''Java'', from [[Java coffee]].<ref>"[http://www.javaworld.com/jw-10-1996/jw-10-javaname.html So why did they decide to call it Java?]", Kieron Murphy, JavaWorld.com, 10/04/96</ref> Gosling designed Java with a C/C++-style syntax that system and application programmers would find familiar.<ref>Kabutz, Heinz; [http://www.artima.com/weblogs/viewpost.jsp?thread=7555 ''Once Upon an Oak'']. Artima. Retrieved April 29, 2007.</ref>

[[Sun Microsystems]] released the first public implementation as Java 1.0 in 1995.<ref name="oraclejavahistory">{{cite web | url=http://www.oracle.com/technetwork/java/javase/overview/javahistory-index-198355.html | title=The History of Java Technology | accessdate=October 6, 2012}}</ref> It promised "Write Once, Run Anywhere" (WORA), providing no-cost run-times on popular [[Computing platform|platforms]]. Fairly secure and featuring configurable security, it allowed network- and file-access restrictions. Major [[web browser]]s soon incorporated the ability to run ''[[Java applet]]s'' within web pages, and Java quickly became popular. The Java 1.0 compiler was re-written [[Bootstrapping (compilers)|in Java]] by [[Arthur van Hoff]] to comply strictly with the Java 1.0 language specification.<ref>{{cite book | url=https://books.google.com/books?id=rXGMFYXFDwMC | title= Object-oriented Programming with Java: Essentials and Applications | publisher=Tata McGraw-Hill Education | page=34}}</ref> With the advent of ''Java 2'' (released initially as J2SE 1.2 in December 1998 – 1999), new versions had multiple configurations built for different types of platforms. ''J2EE'' included technologies and APIs for enterprise applications typically run in server environments, while ''J2ME'' featured APIs optimized for mobile applications. The desktop version was renamed ''J2SE''. In 2006, for marketing purposes, Sun renamed new ''J2'' versions as ''[[Java Platform, Enterprise Edition|Java EE]]'', ''[[Java Platform, Micro Edition|Java ME]]'', and ''[[Java Platform, Standard Edition|Java SE]]'', respectively.

In 1997, Sun Microsystems approached the [[ISO/IEC JTC 1]] standards body and later the [[Ecma International]] to formalize Java, but it soon withdrew from the process.<ref>{{cite web|url=http://www.open-std.org/JTC1/SC22/JSG/|title=JSG – Java Study Group|work=open-std.org}}</ref><ref>{{cite web | url=http://csdl2.computer.org/comp/proceedings/hicss/2001/0981/05/09815015.pdf |title=Why Java™ Was – Not – Standardized Twice}}</ref><ref>{{cite web|url=http://www.zdnet.com/news/what-is-ecma-and-why-microsoft-cares/298821 |title=What is ECMA—and why Microsoft cares}}</ref> Java remains a [[de facto standard|''de facto'' standard]], controlled through the [[Java Community Process]].<ref>{{cite web |url=http://www.jcp.org/en/home/index |title=Java Community Process website |publisher=Jcp.org |date=May 24, 2010 |accessdate=2010-06-09 }}</ref> At one time, Sun made most of its Java implementations available without charge, despite their [[proprietary software]] status. Sun generated revenue from Java through the selling of licenses for specialized products such as the Java Enterprise System.

On November 13, 2006, Sun released much of its Java virtual machine (JVM) as [[free and open-source software]], (FOSS), under the terms of the [[GNU General Public License]] (GPL). On May 8, 2007, Sun finished the process, making all of its JVM's core code available under [[free software]]/open-source distribution terms, aside from a small portion of code to which Sun did not hold the copyright.<ref>{{cite web |url=http://grnlight.net/index.php/programming-articles/115-javaone-sun-the-bulk-of-java-is-open-sourced |title=JAVAONE: Sun – The bulk of Java is open sourced |publisher=GrnLight.net |accessdate=2014-05-26}}</ref>

Sun's vice-president Rich Green said that Sun's ideal role with regard to Java was as an "evangelist".<ref>{{cite web
|url=http://onjava.com/pub/a/onjava/2002/04/17/evangelism.html
|title=Sun's Evolving Role as Java Evangelist
|publisher=[[O'Reilly Media]]}}</ref> Following [[Oracle Corporation]]'s acquisition of Sun Microsystems in 2009–10, Oracle has described itself as the "steward of Java technology with a relentless commitment to fostering a community of participation and transparency".<ref>{{cite web
 |url=http://www.oracle.com/us/technologies/java/index.html 
 |title=Oracle and Java 
 |work=oracle.com 
 |publisher=Oracle Corporation 
 |accessdate=2010-08-23 
 |quote=Oracle has been a leading and substantive supporter of Java since its emergence in 1995 and takes on the new role as steward of Java technology with a relentless commitment to fostering a community of participation and transparency. 
 |deadurl=bot: unknown 
 |archiveurl=https://web.archive.org/web/20100131091008/http://www.oracle.com/us/technologies/java/index.html 
 |archivedate=January 31, 2010 
 |df= 
}}</ref> This did not prevent Oracle from filing a lawsuit against Google shortly after that for using Java inside the Android SDK (see Google section below). Java software runs on everything from laptops to [[data center]]s, [[Video game console|game consoles]] to scientific [[supercomputer]]s.<ref>{{cite web|title=Learn About Java Technology|url=http://www.java.com/en/about/|publisher=Oracle|accessdate=November 21, 2011}}</ref> On April 2, 2010, James Gosling resigned from Oracle.<ref>{{cite web|url=http://nighthacks.com/roller/jag/entry/time_to_move_on |title=Time to move on... |last=Gosling |first=James |date=April 9, 2010 |work=On a New Road |accessdate=2011-11-16 |authorlink=James Gosling |deadurl=bot: unknown |archiveurl=https://web.archive.org/web/20101105031239/http://nighthacks.com/roller/jag/entry/time_to_move_on |archivedate=November 5, 2010 |df= }}</ref>

In January 2016, Oracle announced that Java runtime environments based on JDK 9 will discontinue the browser plugin.<ref>{{cite web|url=https://blogs.oracle.com/java-platform-group/entry/moving_to_a_plugin_free|title=Moving to a Plugin-Free Web|first=Dalibor|last=Topic|publisher=}}</ref>

===Principles===
There were five primary goals in the creation of the Java language:<ref name="design_goals"/>

<!--NOTE: THESE 5 ARE QUOTED DIRECTLY FROM THE SOURCE. DON'T REMOVE ANY OR ADD "NEW" ONES!-->
# It must be "simple, object-oriented, and familiar".
# It must be "robust and secure".
# It must be "architecture-neutral and portable".
# It must execute with "high performance".
# It must be "interpreted, threaded, and dynamic".
<!--NOTE: THESE 5 ARE QUOTED DIRECTLY FROM THE SOURCE. DON'T REMOVE ANY OR ADD "NEW" ONES!-->

===Versions===
{{Main|Java version history}}

{{As of|2017}}, both Java 8 and 9 are officially supported. Major release versions of Java, along with their release dates:

* JDK 1.0 (January 23, 1996)<ref>{{cite web|url=http://www.sun.com/smi/Press/sunflash/1996-01/sunflash.960123.10561.xml |title=JAVASOFT SHIPS JAVA 1.0 |accessdate=2008-02-05 |deadurl=yes |archiveurl=https://web.archive.org/web/20070310235103/http://www.sun.com/smi/Press/sunflash/1996-01/sunflash.960123.10561.xml |archivedate=March 10, 2007 |df= }}</ref>
* JDK 1.1 (February 19, 1997)
* J2SE 1.2 (December 8, 1998)
* J2SE 1.3 (May 8, 2000)
* J2SE 1.4 (February 6, 2002)
* J2SE 5.0 (September 30, 2004)
* Java SE 6 (December 11, 2006)
* Java SE 7 (July 28, 2011)
* Java SE 8 (March 18, 2014)
* Java SE 9 (September 21, 2017)

==Practices==

===Java platform===
{{Main|Java (software platform)|Java virtual machine}}
<!-- we apparently have two main sections for what seems to be the same thing. Merge needed? -->

One design goal of Java is portability, which means that programs written for the Java platform must run similarly on any combination of hardware and operating system with adequate runtime support.
This is achieved by compiling the Java language code to an intermediate representation called [[Java bytecode]], instead of directly to architecture-specific [[machine code]]. Java bytecode instructions are analogous to machine code, but they are intended to be executed by a [[virtual machine]] (VM) written specifically for the host hardware. [[End user]]s commonly use a [[Java virtual machine|Java Runtime Environment]] (JRE) installed on their own machine for standalone Java applications, or in a web browser for Java [[applet]]s.

Standard libraries provide a generic way to access host-specific features such as graphics, [[thread (computing)|threading]], and [[Computer network|networking]].

The use of universal bytecode makes porting simple. However, the overhead of interpreting bytecode into machine instructions made interpreted programs almost always run more slowly than native [[executable]]s. [[Just-in-time compilation|Just-in-time]] (JIT) compilers that compile bytecodes to machine code during runtime were introduced from an early stage. Java itself is platform-independent and is adapted to the particular platform it is to run on by a [[Java virtual machine]] for it, which translates the [[Java bytecode]] into the platform's machine language.<ref>{{cite web|url=http://www.programmerinterview.com/index.php/java-questions/jvm-platform-dependent/|title=Is the JVM (Java Virtual Machine) platform dependent or platform independent? What is the advantage of using the JVM, and having Java be a translated language?|publisher=Programmer Interview|accessdate=2015-01-19}}</ref>

====Implementations====
{{See also|Free Java implementations}}

[[Oracle Corporation]] is the current owner of the official implementation of the Java SE platform, following their acquisition of [[Sun Microsystems]] on January 27, 2010. This implementation is based on the original implementation of Java by Sun. The Oracle implementation is available for [[Microsoft Windows]] (still works for XP, while only later versions currently officially supported), [[macOS]], [[Linux]], and [[Solaris (operating system)|Solaris]]. Because Java lacks any formal standardization recognized by [[Ecma International]], ISO/IEC, ANSI, or other third-party standards organization, the Oracle implementation is the [[de facto standard]].

The Oracle implementation is packaged into two different distributions: The Java Runtime Environment (JRE) which contains the parts of the Java SE platform required to run Java programs and is intended for end users, and the [[Java Development Kit]] (JDK), which is intended for software developers and includes development tools such as the [[Java compiler]], [[Javadoc]], [[JAR (file format)|Jar]], and a [[debugger]].

[[OpenJDK]] is another notable Java SE implementation that is licensed under the GNU GPL. The implementation started when Sun began releasing the Java source code under the GPL. As of Java SE 7, OpenJDK is the official Java reference implementation.

The goal of Java is to make all implementations of Java compatible. Historically, Sun's trademark license for usage of the Java brand insists that all implementations be "compatible". This resulted in a legal dispute with [[Microsoft]] after Sun claimed that the Microsoft implementation did not support [[Java remote method invocation|RMI]] or [[Java Native Interface|JNI]] and had added platform-specific features of their own. Sun sued in 1997, and, in 2001, won a settlement of US$20&nbsp;million, as well as a court order enforcing the terms of the license from Sun.<ref>{{cite news |author=Niccolai, James |title=Sun, Microsoft settle Java lawsuit |url=http://www.javaworld.com/javaworld/jw-01-2001/jw-0124-iw-mssuncourt.html |work=JavaWorld |publisher=[[International Data Group]] |date=January 23, 2001 |accessdate=2008-07-09 }}</ref> As a result, Microsoft no longer ships Java with [[Microsoft Windows|Windows]].

Platform-independent Java is essential to [[Java Platform, Enterprise Edition|Java EE]], and an even more rigorous validation is required to certify an implementation. This environment enables portable server-side applications.

====Performance====
{{Main|Java performance}}

Programs written in Java have a reputation for being slower and requiring more memory than those written in C++.<ref>{{cite web |url=http://www.jelovic.com/articles/why_java_is_slow.htm |title=Why Java will always be slower than C++ |last=Jelovic |first=Dejan| accessdate=2008-02-15 }}</ref><ref>{{cite web |url=https://days2011.scala-lang.org/sites/days2011/files/ws3-1-Hundt.pdf |title=Loop Recognition in C++/Java/Go/Scala |last=Google| accessdate=2012-07-12 }}</ref> However, Java programs' execution speed improved significantly with the introduction of [[just-in-time compilation]] in 1997/1998 for [[Java version history|Java 1.1]],<ref>{{cite web |url=http://www.symantec.com/about/news/release/article.jsp?prid=19970407_03 |title=Symantec's Just-In-Time Java Compiler To Be Integrated into Sun JDK 1.1 }}</ref> the addition of language features supporting better code analysis (such as inner classes, the StringBuilder class, optional assertions, etc.), and optimizations in the Java virtual machine, such as [[HotSpot]] becoming the default for Sun's JVM in 2000. With Java 1.5, the performance was improved with the addition of the java.util.concurrent package, including [[Lock free]] implementations of the [[Java ConcurrentMap|ConcurrentMaps]] and other multi-core collections, and it was improved further Java 1.6.

Some platforms offer direct hardware support for Java; there are microcontrollers that can run Java in hardware instead of a software Java virtual machine{{citation needed|date=April 2017}}, and some [[ARM architecture|ARM]] based processors could have hardware support for executing Java bytecode through their [[Jazelle]] option, though support has mostly been dropped in current implementations of ARM.

===Automatic memory management===
Java uses an [[Garbage collection (computer science)|automatic garbage collector]] to manage memory in the [[object lifetime|object lifecycle]]. The programmer determines when objects are created, and the Java runtime is responsible for recovering the memory once objects are no longer in use. Once no references to an object remain, the [[unreachable memory]] becomes eligible to be freed automatically by the garbage collector. Something similar to a [[memory leak]] may still occur if a programmer's code holds a reference to an object that is no longer needed, typically when objects that are no longer needed are stored in containers that are still in use. If methods for a nonexistent object are called, a "null pointer exception" is thrown.<ref>{{cite web |url=http://docs.oracle.com/javase/8/docs/api/java/lang/NullPointerException.html |title=NullPointerException |publisher=Oracle |accessdate=2014-05-06 }}</ref><ref>{{cite web |url=http://www.artima.com/designtechniques/exceptions.html |title=Exceptions in Java |publisher=Artima.com |accessdate=2010-08-10 }}</ref>

One of the ideas behind Java's automatic memory management model is that programmers can be spared the burden of having to perform manual memory management. In some languages, memory for the creation of objects is implicitly allocated on the [[Stack (abstract data type)|stack]] or explicitly allocated and deallocated from the [[Memory management#DYNAMIC|heap]]. In the latter case, the responsibility of managing memory resides with the programmer. If the program does not deallocate an object, a [[memory leak]] occurs. If the program attempts to access or deallocate memory that has already been deallocated, the result is undefined and difficult to predict, and the program is likely to become unstable or crash. This can be partially remedied by the use of [[smart pointer]]s, but these add overhead and complexity. Note that garbage collection does not prevent "logical" memory leaks, ''i.e.'', those where the memory is still referenced but never used.

Garbage collection may happen at any time. Ideally, it will occur when a program is idle. It is guaranteed to be triggered if there is insufficient free memory on the heap to allocate a new object; this can cause a program to stall momentarily. Explicit memory management is not possible in Java.

Java does not support C/C++ style [[pointer (computer programming)|pointer arithmetic]], where object addresses and unsigned integers (usually long integers) can be used interchangeably. This allows the garbage collector to relocate referenced objects and ensures type safety and security.

As in C++ and some other object-oriented languages, variables of Java's [[primitive data type]]s are either stored directly in fields (for objects) or on the [[Stack-based memory allocation|stack]] (for methods) rather than on the heap, as is commonly true for non-primitive data types (but see [[escape analysis]]). This was a conscious decision by Java's designers for performance reasons.

Java contains multiple types of garbage collectors. By default, HotSpot uses the [[parallel scavenge garbage collector]].<ref>{{cite web|url=http://docs.oracle.com/javase/7/docs/technotes/guides/vm/performance-enhancements-7.html |title=Java HotSpot™ Virtual Machine Performance Enhancements |publisher=Oracle.com |accessdate=2017-04-26}}</ref> However, there are also several other garbage collectors that can be used to manage the heap. For 90% of applications in Java, the [[Concurrent mark sweep collector|Concurrent Mark-Sweep]] (CMS) garbage collector is sufficient.<ref>{{cite web|url=http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html |title=Java HotSpot VM Options |publisher=Oracle.com |date=September 7, 2010 |accessdate=2012-06-30}}</ref> Oracle aims to replace CMS with the [[Garbage-First collector]] (G1).<ref>{{cite web|url=http://docs.oracle.com/javase/7/docs/technotes/guides/vm/G1.html|title=Garbage-First Collector|website=docs.oracle.com}}</ref>

==Syntax==
{{Main|Java syntax}}

The syntax of Java is largely influenced by [[C++]]. Unlike C++, which combines the syntax for structured, generic, and object-oriented programming, Java was built almost exclusively as an object-oriented language.<ref name="design_goals"/> All code is written inside classes, and every data item is an object, with the exception of the primitive data types, (''i.e.'' integers, floating-point numbers, [[Boolean data type|boolean values]], and characters), which are not objects for performance reasons. Java reuses some popular aspects of C++ (such as printf() method).

Unlike C++, Java does not support [[operator overloading]]<ref name="msdn_operator_overloading">{{cite web | url=http://msdn.microsoft.com/en-us/library/ms228498%28v=vs.90%29.aspx | title=Operator Overloading (C# vs Java) | publisher=Microsoft| work=C# for Java Developers | accessdate=December 10, 2014}}</ref> or [[multiple inheritance]] for ''classes'', though multiple inheritance is supported for [[interface (Java)|interface]]s.<ref name="oracle_multiple_inheritance">{{cite web | url=https://docs.oracle.com/javase/tutorial/java/IandI/multipleinheritance.html | title=Multiple Inheritance of State, Implementation, and Type | publisher=Oracle | work=The Java™ Tutorials | accessdate=December 10, 2014}}</ref>

Java uses comments similar to those of C++. There are three different styles of comments: a single line style marked with two slashes (<code>//</code>), a multiple line style opened with <code>/*</code> and closed with <code>*/</code>, and the [[Javadoc]] commenting style opened with <code>/**</code> and closed with <code>*/</code>. The Javadoc style of commenting allows the user to run the Javadoc executable to create documentation for the program and can be read by some [[integrated development environment]]s (IDEs) such as [[Eclipse (software)|Eclipse]] to allow developers to access documentation within the IDE.

'''Example:'''

<source lang="java">
// This is an example of a single line comment using two slashes

/* This is an example of a multiple line comment using the slash and asterisk.
 This type of comment can be used to hold a lot of information or deactivate
 code, but it is very important to remember to close the comment. */

package fibsandlies;
import java.util.HashMap;

/**
 * This is an example of a Javadoc comment; Javadoc can compile documentation
 * from this text. Javadoc comments must immediately precede the class, method, or field being documented.
 */
public class FibCalculator extends Fibonacci implements Calculator {
    private static Map<Integer, Integer> memoized = new HashMap<Integer, Integer>();

    /*
     * The main method written as follows is used by the JVM as a starting point for the program.
     */
    public static void main(String[] args) {
        memoized.put(1, 1);
        memoized.put(2, 1);
        System.out.println(fibonacci(12)); //Get the 12th Fibonacci number and print to console
    }

    /**
     * An example of a method written in Java, wrapped in a class.
     * Given a non-negative number FIBINDEX, returns
     * the Nth Fibonacci number, where N equals FIBINDEX.
     * @param fibIndex The index of the Fibonacci number
     * @return The Fibonacci number
     */
    public static int fibonacci(int fibIndex) {
        if (memoized.containsKey(fibIndex)) {
            return memoized.get(fibIndex);
        } else {
            int answer = fibonacci(fibIndex - 1) + fibonacci(fibIndex - 2);
            memoized.put(fibIndex, answer);
            return answer;
        }
    }
}</source>

== "Hello world" example ==
The traditional [["Hello, world!" program]] can be written in Java as:<ref>{{cite web |url=http://download.oracle.com/javase/tutorial/getStarted/application/index.html |title=Lesson: A Closer Look at the "Hello World!" Application |work=The Java™ Tutorials > Getting Started |publisher=[[Oracle Corporation]] |accessdate=2011-04-14 }}</ref>
<!--
NOTE:
PLEASE *don't* change the example code; it's written in Sun's recommended style. That includes the brace style.
 -->
<source lang="java">
class HelloWorldApp {
    public static void main(String[] args) {
        System.out.println("Hello World!"); // Prints the string to the console.
    }
}
</source>

Source files must be named after the public class they contain, appending the suffix <code>.java</code>, for example, <code>HelloWorldApp.java</code>. It must first be compiled into bytecode, using a [[Java compiler]], producing a file named <code>HelloWorldApp.class</code>. Only then can it be executed, or "launched". The Java source file may only contain one public class, but it can contain multiple classes with other than public access and any number of public [[inner class]]es. When the source file contains multiple classes, make one class "public" and name the source file with that public class name.

A <code>'''class'''</code> that is not declared <code>'''public'''</code> may be stored in any .java file. The compiler will generate a class file for each class defined in the source file. The name of the class file is the name of the class, with ''.class'' appended. For class file generation, [[Class (computer programming)#Unnamed|anonymous classes]] are treated as if their name were the concatenation of the name of their enclosing class, a ''$'', and an integer.

The [[List of Java keywords|keyword]] <code>'''public'''</code> denotes that a method can be called from code in other classes, or that a class may be used by classes outside the class hierarchy. The class hierarchy is related to the name of the directory in which the .java file is located. This is called an access level modifier. Other access level modifiers include the keywords <code>'''private'''</code> and <code>'''protected'''</code>.

The keyword <code>'''static'''</code> in front of a method indicates a [[Method (computer programming)#Static methods|static method]], which is associated only with the class and not with any specific instance of that class. Only static methods can be invoked without a reference to an object. Static methods cannot access any class members that are not also static. Methods that are not designated static are instance methods and require a specific instance of a class to operate.

The keyword <code>'''void'''</code> indicates that the main method does not return any value to the caller. If a Java program is to exit with an error code, it must call System.exit() explicitly.

The method name "<code>main</code>" is not a keyword in the Java language. It is simply the name of the method the Java launcher calls to pass control to the program. Java classes that run in managed environments such as applets and [[Enterprise JavaBeans]] do not use or need a <code>main()</code> method. A Java program may contain multiple classes that have <code>main</code> methods, which means that the VM needs to be explicitly told which class to launch from.

The main method must accept an [[array data type|array]] of '''{{Javadoc:SE|java/lang|String}}''' objects. By convention, it is referenced as <code>'''args'''</code> although any other legal identifier name can be used. Since Java 5, the main method can also use [[variadic function|variable arguments]], in the form of <code>public static void main(String... args)</code>, allowing the main method to be invoked with an arbitrary number of <code>String</code> arguments. The effect of this alternate declaration is semantically identical (the <code>args</code> parameter is still an array of <code>String</code> objects), but it allows an alternative syntax for creating and passing the array.

The Java launcher launches Java by loading a given class (specified on the command line or as an attribute in a [[JAR (file format)|JAR]]) and starting its <code>public static void main(String[])</code> method. Stand-alone programs must declare this method explicitly. The <code>String[] args</code> parameter is an [[array data type|array]] of {{Javadoc:SE|java/lang|String}} objects containing any arguments passed to the class. The parameters to <code>main</code> are often passed by means of a [[command-line interface|command line]].

Printing is part of a Java standard library: The '''{{Javadoc:SE|java/lang|System}}''' class defines a public static field called '''{{Javadoc:SE|name=out|java/lang|System|out}}'''. The <code>out</code> object is an instance of the {{Javadoc:SE|java/io|PrintStream}} class and provides many methods for printing data to [[standard streams|standard out]], including '''{{Javadoc:SE|name=println(String)|java/io|PrintStream|println(java.lang.String)}}''' which also appends a new line to the passed string.

The string "Hello World!" is automatically converted to a String object by the compiler.

==Special classes==
{{Howto|section|date=January 2012}}

===Applet===
{{Main|Java applet}}

Java applets are programs that are [[Embedded system#Embedded software architectures|embedded]] in other applications, typically in a Web page displayed in a web browser.

<source lang="java">
// Hello.java
import javax.swing.JApplet;
import java.awt.Graphics;

public class Hello extends JApplet {
    public void paintComponent(final Graphics g) {
        g.drawString("Hello, world!", 65, 95);
    }
}
</source>

The <code>'''import'''</code> statements direct the [[Java compiler]] to include the '''{{Javadoc:SE|package=javax.swing|javax/swing|JApplet}}''' and '''{{Javadoc:SE|package=java.awt|java/awt|Graphics}}''' classes in the compilation. The import statement allows these classes to be referenced in the [[source code]] using the ''simple class name'' (i.e. <code>JApplet</code>) instead of the ''fully qualified class name'' (''FQCN'', i.e. <code>javax.swing.JApplet</code>).

The <code>Hello</code> class <code>'''extends'''</code> ([[Inheritance (object-oriented programming)#Subclasses and superclasses|subclasses]]) the <code>'''JApplet'''</code> (Java Applet) class; the <code>JApplet</code> class provides the framework for the host application to display and control the [[Object lifetime|lifecycle]] of the applet. The <code>JApplet</code> class is a JComponent (Java Graphical Component) which provides the applet with the capability to display a [[graphical user interface]] (GUI) and respond to user [[event-driven programming|events]].

The <code>Hello</code> class [[Method overriding|overrides]] the '''{{Javadoc:SE|name=paintComponent(Graphics)|java/awt|Container|paint(java.awt.Graphics)}}''' method (additionally indicated with the [[Java annotation|annotation]], supported as of JDK 1.5, <code>Override</code>) inherited from the {{Javadoc:SE|java/awt|Container}} [[Inheritance (object-oriented programming)#Subclasses and superclasses|superclass]] to provide the code to display the applet. The <code>paintComponent()</code> method is passed a <code>'''Graphics'''</code> object that contains the graphic context used to display the applet. The <code>paintComponent()</code> method calls the graphic context '''{{Javadoc:SE|name=drawString(String, int, int)|java/awt|Graphics|drawString(java.lang.String,%20int,%20int)}}''' method to display the '''"Hello, world!"''' string at a [[pixel]] offset of (<code>'''65, 95'''</code>) from the upper-left corner in the applet's display.

<source lang="html4strict">
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<!-- Hello.html -->
<html>
    <head>
        <title>Hello World Applet</title>
    </head>
    <body>
        <applet code="Hello.class" width="200" height="200">
        </applet>
    </body>
</html>
</source>

An applet is placed in an [[HTML]] document using the '''<code>&lt;applet&gt;</code>''' [[HTML element]]. The <code>applet</code> tag has three attributes set: '''<code>code="Hello.class"</code>''' specifies the name of the <code>JApplet</code> class and '''<code>width="200" height="200"</code>''' sets the pixel width and height of the applet. Applets may also be embedded in HTML using either the <code>object</code> or <code>embed</code> element,<ref>{{cite web |url=http://download.oracle.com/javase/1.5.0/docs/guide/plugin/developer_guide/using_tags.html |title=Using applet, object and embed Tags |publisher=oracle.com |accessdate=2010-10-14 }}</ref> although support for these elements by web browsers is inconsistent.<ref>{{cite web |url=http://download.oracle.com/javase/1.5.0/docs/guide/plugin/developer_guide/using_tags.html#mixed |title=Deploying Applets in a Mixed-Browser Environment |publisher=oracle.com |accessdate=2010-10-14 }}</ref> However, the <code>applet</code> tag is deprecated, so the <code>object</code> tag is preferred where supported.

The host application, typically a Web browser, instantiates the '''<code>Hello</code>''' applet and creates an {{Javadoc:SE|java/applet|AppletContext}} for the applet. Once the applet has initialized itself, it is added to the AWT display hierarchy. The <code>paintComponent()</code> method is called by the AWT [[event dispatching thread]] whenever the display needs the applet to draw itself.

===Servlet===
{{Main|Java Servlet}}

[[Java Servlet]] technology provides Web developers with a simple, consistent mechanism for extending the functionality of a Web server and for accessing existing business systems. Servlets are [[server-side]] Java EE components that generate responses (typically [[HTML]] pages) to requests (typically [[Hypertext Transfer Protocol|HTTP]] requests) from [[client (computing)|clients]]. A servlet can almost be thought of as an applet that runs on the server side—without a face.

<source lang="java">
// Hello.java
import java.io.*;
import javax.servlet.*;

public class Hello extends GenericServlet {
    public void service(final ServletRequest request, final ServletResponse response)
    throws ServletException, IOException {
        response.setContentType("text/html");
        final PrintWriter pw = response.getWriter();
        try {
            pw.println("Hello, world!");
        } finally {
            pw.close();
        }
    }
}
</source>

The '''<code>import</code>''' statements direct the Java compiler to include all the public classes and [[interface (Java)|interfaces]] from the '''{{Javadoc:SE|package=java.io|java/io}}''' and '''{{Javadoc:EE|package=javax.servlet|javax/servlet}}''' packages in the compilation.  Packages make Java well suited for large scale applications.

The <code>'''Hello'''</code> class <code>'''extends'''</code> the '''{{Javadoc:EE|javax/servlet|GenericServlet}}''' class; the <code>GenericServlet</code> class provides the interface for the [[server (computing)|server]] to forward requests to the servlet and control the servlet's lifecycle.

The <code>Hello</code> class overrides the '''{{Javadoc:EE|name=service(ServletRequest, ServletResponse)|javax/servlet|Servlet|service(javax.servlet.ServletRequest,javax.servlet.ServletResponse)}}''' method defined by the {{Javadoc:EE|javax/servlet|Servlet}} [[Interface (Java)|interface]] to provide the code for the service request handler. The <code>service()</code> method is passed: a '''{{Javadoc:EE|javax/servlet|ServletRequest}}''' object that contains the request from the client and a '''{{Javadoc:EE|javax/servlet|ServletResponse}}''' object used to create the response returned to the client. The <code>service()</code> method declares that it <code>'''throws'''</code> the [[exception handling|exceptions]] {{Javadoc:EE|javax/servlet|ServletException}} and {{Javadoc:SE|java/io|IOException}} if a problem prevents it from responding to the request.

The '''{{Javadoc:EE|name=setContentType(String)|javax/servlet|ServletResponse|setContentType(java.lang.String)}}''' method in the response object is called to set the [[MIME]] content type of the returned data to '''"text/html"'''. The '''{{Javadoc:EE|name=getWriter()|javax/servlet|ServletResponse|getWriter()}}''' method in the response returns a '''{{Javadoc:SE|java/io|PrintWriter}}''' object that is used to write the data that is sent to the client. The '''{{Javadoc:SE|name=println(String)|java/io|PrintWriter|println(java.lang.String)}}''' method is called to write the '''"Hello, world!"''' string to the response and then the '''{{Javadoc:SE|name=close()|java/io|PrintWriter|close()}}''' method is called to close the print writer, which causes the data that has been written to the stream to be returned to the client.

===JavaServer Pages===
{{Main|JavaServer Pages}}

JavaServer Pages (JSP) are [[server-side]] Java EE components that generate responses, typically [[HTML]] pages, to [[Hypertext Transfer Protocol|HTTP]] requests from [[client (computing)|clients]]. JSPs embed Java code in an HTML page by using the special [[delimiter]]s <code><%</code> and <code>%></code>. A JSP is compiled to a Java ''servlet'', a Java application in its own right, the first time it is accessed. After that, the generated servlet creates the response.

===Swing application===
{{Main|Swing (Java)}}

[[Swing (Java)|Swing]] is a graphical user interface [[library (computing)|library]] for the Java SE platform. It is possible to specify a different look and feel through the [[pluggable look and feel]] system of Swing. Clones of [[Microsoft Windows|Windows]], [[GTK+]], and [[Motif (software)|Motif]] are supplied by Sun. [[Apple Inc.|Apple]] also provides an [[Aqua (user interface)|Aqua]] look and feel for [[macOS]]. Where prior implementations of these looks and feels may have been considered lacking, Swing in Java SE 6 addresses this problem by using more native [[Graphical control element|GUI widget]] drawing routines of the underlying platforms.

This example Swing application creates a single window with "Hello, world!" inside:

<source lang="java">
// Hello.java (Java SE 5)
import javax.swing.*;

public class Hello extends JFrame {
    public Hello() {
        super("hello");
        super.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        super.add(new JLabel("Hello, world!"));
        super.pack();
        super.setVisible(true);
    }

    public static void main(final String[] args) {
        new Hello();
    }
}
</source>

The first '''<code>import</code>''' includes all the public classes and interfaces from the '''{{Javadoc:SE|package=javax.swing|javax/swing}}''' package.

The <code>'''Hello'''</code> class <code>'''extends'''</code> the '''{{Javadoc:SE|javax/swing|JFrame}}''' class; the <code>JFrame</code> class implements a [[window (computing)|window]] with a [[title bar]] and a close [[Graphical control element|control]].

The <code>'''Hello()'''</code> [[constructor (object-oriented programming)|constructor]] initializes the frame by first calling the superclass constructor, passing the parameter <code>"hello"</code>, which is used as the window's title. It then calls the '''{{Javadoc:SE|name=setDefaultCloseOperation(int)|javax/swing|JFrame|setDefaultCloseOperation(int)}}''' method inherited from <code>JFrame</code> to set the default operation when the close control on the title bar is selected to '''{{Javadoc:SE|javax/swing|WindowConstants|EXIT_ON_CLOSE}}'''{{snd}} this causes the <code>JFrame</code> to be disposed of when the frame is closed (as opposed to merely hidden), which allows the Java virtual machine to exit and the program to terminate. Next, a '''{{Javadoc:SE|javax/swing|JLabel}}''' is created for the string '''"Hello, world!"''' and the '''{{Javadoc:SE|name=add(Component)|java/awt|Container|add(java.awt.Component)}}''' method inherited from the {{Javadoc:SE|java/awt|Container}} superclass is called to add the label to the frame. The '''{{Javadoc:SE|name=pack()|java/awt|Window|pack()}}''' method inherited from the {{Javadoc:SE|java/awt|Window}} superclass is called to size the window and lay out its contents.

The <code>'''main()'''</code> method is called by the Java virtual machine when the program starts. It [[Object (computer science)|instantiates]] a new '''<code>Hello</code>''' frame and causes it to be displayed by calling the '''{{Javadoc:SE|name=setVisible(boolean)|java/awt|Component|setVisible(boolean)}}''' method inherited from the {{Javadoc:SE|java/awt|Component}} superclass with the boolean parameter <code>'''true'''</code>. Once the frame is displayed, exiting the <code>main</code> method does not cause the program to terminate because the AWT [[event dispatching thread]] remains active until all of the Swing top-level windows have been disposed.

===Generics===
{{Main|Generics in Java}}

In 2004, [[generic programming|generics]] were added to the Java language, as part of J2SE 5.0. Prior to the introduction of generics, each variable declaration had to be of a specific type. For container classes, for example, this is a problem because there is no easy way to create a container that accepts only specific types of objects. Either the container operates on all subtypes of a class or interface, usually <code>Object</code>, or a different container class has to be created for each contained class. Generics allow compile-time type checking without having to create many container classes, each containing almost identical code. In addition to enabling more efficient code, certain runtime exceptions are prevented from occurring, by issuing compile-time errors. If Java prevented all runtime type errors (<code>ClassCastException</code>'s) from occurring, it would be [[type safety|type safe]].

In 2016, the type system was shown not to be safe at all, it was proven [[soundness|unsound]].<ref>{{cite web|url=https://raw.githubusercontent.com/namin/unsound/master/doc/unsound-oopsla16.pdf|title=Java and Scala's Type Systems are Unsound}}</ref>

==Criticism==
{{Main|Criticism of Java}}

Criticisms directed at Java include the implementation of generics,<ref>{{cite web
 |last=Arnold 
 |first=Ken 
 |title=Generics Considered Harmful 
 |url=https://weblogs.java.net/blog/arnold/archive/2005/06/generics_consid_1.html 
 |publisher=java.net 
 |accessdate=September 10, 2015 
 |deadurl=bot: unknown 
 |archiveurl=https://web.archive.org/web/20071010002142/http://weblogs.java.net/blog/arnold/archive/2005/06/generics_consid_1.html 
 |archivedate=October 10, 2007 
 |df= 
}}. More comments to the original article available at earlier archive snapshots like .</ref> speed,<ref>{{cite web
|last=Jelovic |first=Dejan
|title=Why Java Will Always Be Slower than C++
|url=http://www.jelovic.com/articles/why_java_is_slow.htm
|publisher=www.jelovic.com
|accessdate=October 17, 2012}}</ref> the handling of unsigned numbers,<ref>{{cite web
|last=Owens |first=Sean R.
|url=http://darksleep.com/player/JavaAndUnsignedTypes.html
|archiveurl=https://web.archive.org/web/20090220171410/http://darksleep.com/player/JavaAndUnsignedTypes.html
|archivedate=February 20, 2009 |title=Java and unsigned int, unsigned short, unsigned byte, unsigned long, etc. (Or rather, the lack thereof)
|accessdate=2011-07-04 }}</ref> the implementation of floating-point arithmetic,<ref>{{cite web
|last=Kahan |first=William
|title=How Java's Floating-Point Hurts Everyone Everywhere
|url=http://www.cs.berkeley.edu/~wkahan/JAVAhurt.pdf
|publisher=Electrical Engineering & Computer Science, University of California at Berkeley
|accessdate=June 4, 2011 }}</ref> and a history of security vulnerabilities in the primary Java VM implementation [[HotSpot]].<ref>{{cite web
|url=http://blogs.technet.com/b/mmpc/archive/2010/10/18/have-you-checked-the-java.aspx
|title=Have you checked the Java?}}
</ref>

==Use outside the Java platform==
The Java programming language requires the presence of a software platform in order for compiled programs to be executed. Oracle supplies the [[Java platform]] for use with Java. The [[Android SDK]] is an alternative software platform, used primarily for developing [[Android application]]s.

===Android===
[[File:Android 6.0-en.png|thumb|upright|The [[Android (operating system)|Android]] operating system makes extensive use of Java-related technology.]]

The Java language is a key pillar in [[Android (operating system)|Android]], an [[open source]] [[mobile operating system]]. Although Android, built on the [[Linux kernel]], is written largely in C, the [[Android software development#SDK|Android SDK]] uses the Java language as the basis for Android applications. The bytecode language supported by the Android SDK is incompatible with Java bytecode and runs on its own virtual machine, optimized for low-memory devices such as [[smartphone]]s and [[tablet computer]]s.
Depending on the Android version, the bytecode is either interpreted by the [[Dalvik virtual machine]] or compiled into native code by the [[Android Runtime]].

Android does not provide the full Java SE standard library, although the Android SDK does include an independent implementation of a large subset of it. It supports Java 6 and some Java 7 features, offering an implementation compatible with the standard library ([[Apache Harmony]]).

====Controversy====
{{See also|Oracle America, Inc. v. Google, Inc.}}
The use of Java-related technology in Android led to a legal dispute between Oracle and Google. On May 7, 2012, a San Francisco jury found that if APIs could be copyrighted, then Google had infringed Oracle's copyrights by the use of Java in Android devices.<ref>{{cite web|last=Mullin|first=Joe|title=Google guilty of infringement in Oracle trial; future legal headaches loom|url=https://arstechnica.com/tech-policy/news/2012/05/jury-rules-google-violated-copyright-law-google-moves-for-mistrial.ars|work=Law & Disorder|publisher=Ars Technica|accessdate=May 8, 2012}}</ref> District Judge [[William Haskell Alsup]] ruled on May 31, 2012, that APIs cannot be copyrighted,<ref>
{{cite web
| title = Google wins crucial API ruling, Oracle's case decimated
| url = https://arstechnica.com/tech-policy/2012/05/google-wins-crucial-api-ruling-oracles-case-decimated/
| author = Joe Mullin
| work = Ars Technica
| date = May 31, 2012
| accessdate = 2012-06-01
 }}
</ref> but this was reversed by the United States Court of Appeals for the Federal Circuit in May 2014.<ref name="cnet appeals">{{cite news | url=http://www.cnet.com/news/court-sides-with-oracle-over-android-in-java-patent-appeal/ | title=Court sides with Oracle over Android in Java patent appeal | work=CNET | date=May 9, 2014 | accessdate=2014-05-10 | author=Rosenblatt, Seth}}</ref> On May 26, 2016, the district court decided in favor of Google, ruling the copyright infringement of the Java API in Android constitutes fair use.<ref>{{cite news|last1=Mullin|first1=Joe|title=Google beats Oracle—Android makes "fair use" of Java APIs|url=https://arstechnica.com/tech-policy/2016/05/google-wins-trial-against-oracle-as-jury-finds-android-is-fair-use/|accessdate=May 26, 2016|publisher=Ars Technica|date=May 26, 2016}}</ref>

==Class libraries==
{{Refimprove section|date=December 2014}}
{{Main|Java Class Library}}

The [[Java Class Library]] is the [[standard library]], developed to support application development in Java. It is controlled by [[Sun Microsystems]] in cooperation with others through the [[Java Community Process]] program. Companies or individuals participating in this process can influence the design and development of the APIs. This process has been a subject of controversy.{{when|date=December 2014}} The class library contains features such as:

* The core libraries, which include:
** IO/NIO
** Networking
** [[Reflection (computer programming)|Reflection]]
** [[Concurrent computing|Concurrency]]
** [[Generics in Java|Generics]]
** Scripting/Compiler
** [[Functional programming]] (Lambda, Streaming)
** [[Java collections framework|Collection libraries]] that implement [[data structure]]s such as [[List (abstract data type)|lists]], [[associative array|dictionaries]], [[tree structure|trees]], [[Set (abstract data type)|sets]], [[Queue (abstract data type)|queues]] and [[double-ended queue]], or [[Stack (abstract data type)|stacks]]<ref name="collections">{{cite web | url=http://docs.oracle.com/javase/8/docs/technotes/guides/collections/overview.html | title=Collections Framework Overview | publisher=Oracle | work=Java Documentation | accessdate=December 18, 2014}}</ref>
** [[XML]] Processing (Parsing, Transforming, Validating) libraries
** [[Computer security|Security]]<ref name="security">{{cite web | url=http://docs.oracle.com/javase/8/docs/technotes/guides/security/overview/jsoverview.html | title=Java™ Security Overview | publisher=Oracle | work=Java Documentation | accessdate=December 18, 2014}}</ref>
** [[Internationalization and localization]] libraries<ref name="i18n">{{cite web | url=http://docs.oracle.com/javase/tutorial/i18n/ | title=Trail: Internationalization | publisher=Oracle | work=The Java™ Tutorials | accessdate=December 18, 2014}}</ref>
* The integration libraries, which allow the application writer to communicate with external systems. These libraries include:
** The [[Java Database Connectivity]] (JDBC) [[Application programming interface|API]] for database access
** [[Java Naming and Directory Interface]] (JNDI) for lookup and discovery
** [[Java remote method invocation|RMI]] and [[Common Object Request Broker Architecture|CORBA]] for distributed application development
** [[Java Management Extensions|JMX]] for managing and monitoring applications
* [[User interface]] libraries, which include:
** The (heavyweight, or [[Native (computing)|native]]) [[Abstract Window Toolkit]] (AWT), which provides [[graphical user interface|GUI]] components, the means for laying out those components and the means for handling events from those components
** The (lightweight) [[Swing (Java)|Swing]] libraries, which are built on AWT but provide (non-native) implementations of the AWT widgetry
** APIs for audio capture, processing, and playback
** [[JavaFX]]
* A platform dependent implementation of the Java virtual machine that is the means by which the bytecodes of the Java libraries and third party applications are executed
* Plugins, which enable [[Java applet|applets]] to be run in web browsers
* [[Java Web Start]], which allows Java applications to be efficiently distributed to [[end user]]s across the Internet
* Licensing and documentation

==Documentation==
{{Main|Javadoc}}

Javadoc is a comprehensive documentation system, created by [[Sun Microsystems]], used by many Java developers{{by whom|date=September 2015}}. It provides developers with an organized system for documenting their code. Javadoc comments have an extra asterisk at the beginning, i.e. the delimiters are <code>/**</code> and <code>*/</code>, whereas the normal multi-line comments in Java are set off with the delimiters <code>/*</code> and <code>*/</code>.<ref name="javadoc_comments">{{cite web | url=http://www.oracle.com/technetwork/articles/java/index-137868.html | title=How to Write Doc Comments for the Javadoc Tool | publisher=Oracle | work=Oracle Technology Network | accessdate=December 18, 2014}}</ref>

==Editions==
{{See also|Free Java implementations#Class library}}
{{Java platforms}}

Sun has defined and supports four editions of Java targeting different application environments and segmented many of its [[application programming interface|APIs]] so that they belong to one of the platforms. The platforms are:

* [[Java Card]] for smartcards.<ref name="java_card">{{cite web | url=http://www.oracle.com/technetwork/java/embedded/javacard/overview/index.html | title=Java Card Overview | publisher=Oracle | work=Oracle Technology Network | accessdate=December 18, 2014}}</ref>
* [[Java Platform, Micro Edition]] (Java ME) – targeting environments with limited resources.<ref name="java_me">{{cite web | url=http://www.oracle.com/technetwork/java/embedded/javame/index.html | title=Java Platform, Micro Edition (Java ME) | publisher=Oracle | work=Oracle Technology Network | accessdate=December 18, 2014}}</ref>
* [[Java Platform, Standard Edition]] (Java SE) – targeting workstation environments.<ref name="java_se">{{cite web | url=http://www.oracle.com/technetwork/java/javase/overview/index.html | title=Java SE | publisher=Oracle | work=Oracle Technology Network | accessdate=December 18, 2014}}</ref>
* [[Java Platform, Enterprise Edition]] (Java EE) – targeting large distributed enterprise or Internet environments.<ref name="java_ee">{{cite web | url=http://www.oracle.com/technetwork/java/javaee/overview/index.html | title=Java Platform, Enterprise Edition (Java EE) | publisher=Oracle | work=Oracle Technology Network | accessdate=December 18, 2014}}</ref>

The [[Class (computer programming)|classes]] in the Java APIs are organized into separate groups called [[Java package|packages]]. Each package contains a set of related [[Interface (Java)|interfaces]], classes, and [[exception handling|exceptions]]. Refer to the separate platforms for a description of the packages available. {{off topic paragraph}}

Sun also provided an edition called [[PersonalJava]] that has been superseded by later, standards-based Java ME configuration-profile pairings.

==See also==
{{Portal|Java|Computer programming}}
{{Wikipedia books|Programming for Students}}

* [[Dalvik (software)|Dalvik]] – used in old Android versions, replaced by non-JIT [[Android Runtime]]
* [[JavaOne]]
* [[Java.net#Javapedia|Javapedia]]
* [[List of Java virtual machines]]
* [[List of Java APIs]]
* [[List of JVM languages]]
* [[Graal (compiler)|Graal]], a project aiming to implement a high performance Java dynamic compiler and interpreter
* [[Spring Framework]]

===Comparison of Java with other languages===
* [[Comparison of programming languages]]
* [[Comparison of Java and C++]]
* [[Comparison of C Sharp and Java|Comparison of C# and Java]]

==Notes==
{{Reflist|30em}}

==References==
{{refbegin}}
* {{cite book|last1=Gosling|first1=James|last2=Joy|first2=Bill|last3=Steele|first3=Guy|last4=Bracha|first4=Gilad|last5=Buckley|first5=Alex|title=The Java® Language Specification|date=2014|edition=Java SE 8|url=https://docs.oracle.com/javase/specs/jls/se8/jls8.pdf|ref=harv}}
* {{cite book |last1=Gosling |first1=James |last2=Joy |first2=Bill |authorlink2=Bill Joy |last3=Steele |first3=Guy L., Jr. |authorlink3=Guy L. Steele, Jr. |first4=Gilad |last4=Bracha |authorlink4=Gilad Bracha |title=The Java Language Specification |url=http://java.sun.com/docs/books/jls/index.html |edition=3rd |year=2005 |publisher=Addison-Wesley |isbn=0-321-24678-0 }}
* {{cite book |last1=Lindholm |first1=Tim |last2=Yellin |first2=Frank |title=The Java Virtual Machine Specification |url=http://java.sun.com/docs/books/vmspec/2nd-edition/html/VMSpecTOC.doc.html |edition=2nd |year=1999 |publisher=Addison-Wesley |isbn=0-201-43294-3 }}
{{refend}}

==External links==
{{Sister project links|wikt=Java|commons=Category:Java (programming language)|v=Java|s=no|b=Subject:Java programming language}}
{{wikiversity|Java Platform, Enterprise Edition/Java EE Tutorial}}
{{Java (software platform)}}
{{Sun Microsystems}}
{{Oracle}}
{{Programming languages}}
{{FOSS}}

{{Authority control}}

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