View source for Java (programming language)

{{Redirect|Java language|the natural language from the Indonesian island of Java|Javanese language}}
{{Distinguish|JavaScript}}
{{pp-pc1|small=yes|expiry=07:35, 1 February 2015 (UTC)}}
{{Infobox programming language
| name = Java
| logo = [[File:Java logo and wordmark.svg|100px]]
| paradigm = [[multi-paradigm programming language|multi-paradigm]]: [[object-oriented programming|object-oriented]], [[structured programming|structured]], [[imperative programming|imperative]],  [[functional programming|functional]], [[generic programming|generic]], [[reflective programming|reflective]], [[Concurrent programming|concurrent]]
| year = {{Start date|1995}}<ref name="oraclejavahistory"/>
| designer = [[James Gosling]] and<br>[[Sun Microsystems]]
| developer = [[Oracle Corporation]]
| written_in = c++
| latest release version = Java Standard Edition 8 Update 20 (1.8.0_20)
| latest release date    = {{Start date and age|2014|08|19}}
| latest preview version = 
| latest preview date    = <!-- {{Start date and age|YYYY|MM|DD}} -->
| frequently updated     = <!-- yes/no -->
| turing-complete = Yes
| typing = [[type system|Static, strong, safe]], [[nominative type system|nominative]], [[manifest typing|manifest]]
| implementations = [[OpenJDK]], [[:Category:Java virtual machine|many others]]
| influenced_by = [[Ada (programming language)|Ada 83]], [[C++]], [[C Sharp (programming language)|C#]],<ref>Java 5.0 added several new language features (the [[foreach|enhanced for loop]], [[autoboxing]], [[variadic function|varargs]] and [[Java annotation|annotations]]), after they were introduced in the similar (and competing) [[C Sharp (programming language)|C#]] language [https://www.barrycornelius.com/papers/java5/] [https://www.levenez.com/lang/]</ref> [[Eiffel (programming language)|Eiffel]],<ref>{{cite web |author=Gosling, James; and McGilton, Henry |title=The Java Language Environment |date=May 1996 |url=https://www.oracle.com/technetwork/java/langenv-140151.html }}</ref> [[Generic Java]], [[Mesa (programming language)|Mesa]],<ref>{{cite web |author=Gosling, James; Joy, Bill; Steele, Guy; and Bracha, Gilad |title=The Java Language Specification, 2nd Edition |url= https://java.sun.com/docs/books/jls/second_edition/html/intro.doc.html#237601 }}</ref> [[Modula-3]],<ref>{{cite web |url=https://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=https://www.delphikingdom.com/asp/viewitem.asp?catalogid=1155}}), that the Sun Java design team licenced 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 -- 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. [https://cs.gmu.edu/~sean/stuff/java-objc.html]</ref> [[UCSD Pascal]],<ref>{{cite web |url=https://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=https://queue.acm.org/detail.cfm?id=1017013 |title=A Conversation with James Gosling – ACM Queue |publisher=Queue.acm.org |date=2004-08-31 |accessdate=2010-06-09 }}</ref> [[Smalltalk]]
| influenced = [[Ada (programming language)|Ada 2005]], [[BeanShell]], [[C Sharp (programming language)|C#]], [[Clojure]], [[D (programming language)|D]], [[ECMAScript]], [[Groovy (programming language)|Groovy]], [[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]]
| programming_language = [[C (programming language)|C]] and [[C++]] 
| operating_system = [[Cross-platform]] (multi-platform) 
| license = [[GNU General Public License]], [[Java Community Process]]
| website = [https://www.oracle.com/technetwork/java/ For Java Developers]
| file_ext = .java , [[Java class file|.class]], [[JAR (file format)|.jar]]
| wikibooks = Java Programming
}}

'''Java''' is a [[computer programming language]] that is [[concurrent computing|concurrent]], [[class-based]], [[Object-oriented programming|object-oriented]], and specifically designed to have as few implementation dependencies as possible. It is intended to let application developers "[[write once, run anywhere]]" (WORA), meaning that code that runs on one platform does not need to be recompiled to run on another. Java applications are typically [[compiler|compiled]] to [[Java bytecode|bytecode]] that can run on any [[Java virtual machine]] (JVM) regardless of [[computer architecture]]. Java is, as of 2014, one of the most popular programming languages in use, particularly for client-server web applications, with a reported 9 million developers.<ref>{{cite web |url=https://www.langpop.com/ |title=Programming Language Popularity |year=2014 |accessdate=2014-02-07 }}</ref><ref>{{cite web |url=https://www.tiobe.com/index.php/content/paperinfo/tpci/index.html |title=TIOBE Programming Community Index |year=2009 |accessdate=2009-05-06 }}</ref> Java was originally developed by [[James Gosling]] at [[Sun Microsystems]] (which has since [[Sun acquisition by Oracle|merged into 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 (computing)|reference implementation]] Java [[compiler]]s, virtual machines, and [[library (computing)|class libraries]] were originally released by Sun under proprietary licences. As of May 2007, in compliance with the specifications of the [[Java Community Process]], Sun 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).

==History==
{{See also|Java (software platform)#History}}

[[File:Wave.svg|thumb|upright|Duke, the Java mascot]]
[[James Gosling]], Mike Sheridan,  and [[Patrick Naughton]] initiated the Java language project in June 1991.<ref>{{cite web |url=https://java.sun.com/features/1998/05/birthday.html |archiveurl=https://web.archive.org/web/20050420081440/https://java.sun.com/features/1998/05/birthday.html |archivedate=2005-04-20 |title=Java technology: The early years |last=Byous |first=Jon |date=c. 1998 |work=Sun Developer Network |publisher=[[Sun Microsystems]] |accessdate=2005-04-22 |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=https://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>"[https://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> said to be consumed in large quantities by the language's creators.{{Citation needed|date=April 2013}} Gosling designed Java with a [[C (programming language)|C]]/[[C++]]-style syntax that system and application programmers would find familiar.<ref>Kabutz, Heinz; [https://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=https://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 JTC1]] standards body and later the [[Ecma International]] to formalize Java, but it soon withdrew from the process.<ref>[https://www.open-std.org/JTC1/SC22/JSG/ Java Study Group]; [https://csdl2.computer.org/comp/proceedings/hicss/2001/0981/05/09815015.pdf Why Java™ Was – Not – Standardized Twice]; [https://www.zdnet.com/news/what-is-ecma-and-why-microsoft-cares/298821 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=https://www.j*****.org/en/home/index |title=Java Community Process website |publisher=J*****.org |date=2010-05-24 |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 Java 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 Java'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=https://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 regards to Java was as an "evangelist."<ref>{{cite web
|url=https://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 2009–2010, 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=https://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. }}</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 [[laptop]]s to [[data center]]s, [[Video game console|game consoles]] to scientific [[supercomputer]]s. There are 930 million [[Java (software platform)|Java Runtime Environment]] downloads each year and 3 billion [[mobile phone]]s run Java.<ref>{{cite web|title=Learn About Java Technology|url=https://www.java.com/en/about/|publisher=Oracle|accessdate=21 November 2011}}</ref> On April 2, 2010, James Gosling resigned from Oracle.<ref>{{cite web|url=https://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}}</ref>

===Principles===
[[File:James Gosling 2008.jpg|thumb|[[James Gosling]], the creator of Java]]
There were five primary goals in the creation of the Java language:<ref>{{cite web 
  |url=https://www.oracle.com/technetwork/java/intro-141325.html 
  |title=1.2 Design Goals of the Java&trade; Programming Language
  |chapter=The Java Language Environment 
  |publisher=Oracle |date=1999-01-01 |accessdate=2013-01-14
}}</ref>
<!--NOTE: THESE 5 ARE QUOTED DIRECTLY FROM THE SOURCE. DON'T REMOVE ANY OR ADD "NEW" ONES!-->
# It should be "simple, object-oriented and familiar"
# It should be "robust and secure"
# It should be "architecture-neutral and portable"
# It should execute with "high performance"
# It should 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}}
Major release versions of Java, along with their release dates:
* JDK 1.0 (January 21, 1996)
* 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)

==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.

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

A major benefit of using bytecode is porting. However, the overhead of interpretation means that interpreted programs almost always run more slowly than programs compiled to native executables would. Just-in-Time (JIT) compilers were introduced from an early stage that compile bytecodes to machine code during runtime.

====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 [[Windows]], [[Mac OS X]], [[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 [[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 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=https://www.javaworld.com/javaworld/jw-01-2001/jw-0124-iw-mssuncourt.html |work=JavaWorld |publisher=[[IDG]] |date=January 23, 2001 |accessdate=2008-07-09 }}</ref> As a result, Microsoft no longer ships [[Microsoft Windows|Windows]] with Java.

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++ (programming language)|C++]].<ref>{{cite web |url=https://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=https://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 itself, such as [[HotSpot]] becoming the default for Sun's JVM in 2000. <!--
========= Note to editors of this page =========
I'm commenting out the following for two reasons: 1) the referenced page is no longer available and 2) the site itself shies away from assigning any quantitative conclusions regarding language-vs-language performance comparisons because of the number of factors (choice of benchmark, implementation of benchmark, runtime environment, hardware, etc.) that determine the outcome. So it's unlikely that the referenced web site would even support such a specific quantitative measurement between the languages even if the page did still exist.
=================================================
As of December 2012, microbenchmarks show Java 7 is approximately 44% slower than C++.<ref>{{cite web|url=https://benchmarksgame.alioth.debian.org/u32q/which-programming-languages-are-fastest.php?gcc=on&javasteady=on&java=on&csharp=on&javaxint=on&calc=chart |title=Which programming languages are fastest? &#124; Computer Language Benchmarks Game |publisher=benchmarksgame.alioth.debian.org |date= |accessdate=2012-06-30}}</ref>
-->

Some platforms offer direct hardware support for Java; there are microcontrollers that can run Java in hardware instead of a software Java virtual machine, and [[ARM architecture|ARM]] based processors can have hardware support for executing Java bytecode through their [[Jazelle]] option.

===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=https://docs.oracle.com/javase/8/docs/api/java/lang/NullPointerException.html |title=NullPointerException |publisher=Oracle |accessdate=2014-05-06 }}</ref><ref>{{cite web |url=https://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 (data structure)|stack]], or explicitly allocated and deallocated from the [[Dynamic memory allocation|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 and/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 not objects. Values of primitive types 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 objects (but see [[escape analysis]]). This was a conscious decision by Java's designers for performance reasons. Because of this, Java was not considered to be a pure object-oriented programming language. However, as of Java 5.0, [[autoboxing]] enables programmers to proceed as if primitive types were instances of their wrapper class.

Java contains multiple types of garbage collectors. By default,{{citation needed|date=June 2013}} HotSpot uses the [[parallel scavenge garbage collector]]. 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]] garbage collector is sufficient.<ref>{{cite web|url=https://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html |title=Java HotSpot VM Options |publisher=Oracle.com |date=2010-09-07 |accessdate=2012-06-30}}</ref> Oracle aims to replace CMS with the [[Garbage-first collector]] (G1).

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

The syntax of Java is largely derived from [[C++]]. Unlike C++, which combines the syntax for structured, generic, and object-oriented programming, Java was built almost exclusively as an object-oriented language. All code is written inside a class, and everything is an object, with the exception of the primitive data types (i.e. integers, floating-point numbers, boolean values, and characters), which are not classes for performance reasons.

Unlike C++, Java does not support [[Operator (programming)|operator]] [[operator overloading|overloading]] or [[multiple inheritance]] for ''classes''. This simplifies the language and aids in preventing potential errors and [[anti-pattern]] design.

Java uses similar commenting methods to 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 compile documentation for the program.

'''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 thing being documented.
 */
public class FibCalculator extends Fibonacci implements Calculator {
    private static HashMap<Integer, Integer> memoized = new HashMap<Integer, Integer>();
    static {
        memoized.put(1, 1);
        memoized.put(2, 1);
    }

    /** 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 itself
     */
    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>

==Examples==
{{Howto|date=January 2012}}

===Hello world===
The traditional [[Hello world program]] can be written in Java as:<ref>{{cite web |url=https://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!"); // Print the string to the console.
    }
}
</source>
To compare this to other programming languages see the list of [[hello world program examples]].

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, [[anonymous class]]es 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.

The keyword <code>'''static'''</code> in front of a method indicates a [[Method (computer science)#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.

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 JavaBean]] 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.

===A more comprehensive example===
{{unreferenced section|date=May 2013}}
{{Howto|date=May 2013}}
<source lang="java">
// OddEven.java
import javax.swing.JOptionPane;

public class OddEven {

    private int userInput; // a whole number("int" means integer)

    /**
     * This is the constructor method. It gets called when an object of the OddEven type
     * is being created.
     */
    public OddEven() {
        /*
         * In most Java programs constructors can initialize objects with default values, or create
         * other objects that this object might use to perform its functions. In some Java programs, the
         * constructor may simply be an empty function if nothing needs to be initialized prior to the
         * functioning of the object. In this program's case, an empty constructor would suffice.
         * A constructor must exist; however, if the user doesn't put one in then the compiler
         * will create an empty one.
         */
    }

    /**
     * This is the main method. It gets called when this class is run through a Java interpreter.
     * @param args command line arguments (unused)
     */
    public static void main(final String[] args) {
       /*
        * This line of code creates a new instance of this class called "number" (also known as an
        * Object) and initializes it by calling the constructor. The next line of code calls
        * the "showDialog()" method, which brings up a prompt to ask you for a number.
        */
       OddEven number = new OddEven();
       number.showDialog();
    }

    public void showDialog() {
        /*
         * "try" makes sure nothing goes wrong. If something does,
         * the interpreter skips to "catch" to see what it should do.
         */
        try {
            /*
             * The code below brings up a JOptionPane, which is a dialog box
             * The String returned by the "showInputDialog()" method is converted into
             * an integer, making the program treat it as a number instead of a word.
             * After that, this method calls a second method, calculate() that will
             * display either "Even" or "Odd."
             */
            userInput = Integer.parseInt(JOptionPane.showInputDialog("Please enter a number."));
            calculate();
        } catch (final NumberFormatException e) {
            /*
             * Getting in the catch block means that there was a problem with the format of
             * the number. Probably some letters were typed in instead of a number.
             */
            System.err.println("ERROR: Invalid input. Please type in a numerical value.");
        }
    }

    /**
     * When this gets called, it sends a message to the interpreter.
     * The interpreter usually shows it on the command prompt (For Windows users)
     * or the terminal (For *nix users).(Assuming it's open)
     */
    private void calculate() {
        if ((userInput % 2) == 0) {
            JOptionPane.showMessageDialog(null, "Even");
        } else {
            JOptionPane.showMessageDialog(null, "Odd");
        }
    }
}
</source>
* The '''[[List of Java keywords#import|import]]''' statement imports the '''{{Javadoc:SE|javax/swing|JOptionPane}}''' class from the '''{{Javadoc:SE|package=javax.swing|javax/swing}}''' [[Java package|package]].
* The <code>'''OddEven'''</code> class declares a single <code>'''[[b:Java Programming/Classes, Objects and Types|private]]'''</code> [[Field (computer science)|field]] of type <code>'''int'''</code> named <code>'''userInput'''</code>. Every instance of the <code>OddEven</code> class has its own copy of the <code>userInput</code> field. The private declaration means that no other class can access (read or write) the <code>userInput</code> field.
* <code>'''OddEven()'''</code> is a <code>'''public'''</code> [[Constructor (object-oriented programming)|constructor]]. Constructors have the same name as the enclosing class they are declared in, and unlike a method, have no [[return type]]. A constructor is used to initialize an [[Object (computer science)|object]] that is a newly created instance of the class.
* The <code>'''calculate()'''</code> method is declared without the [[Static (keyword)|<code>static</code> keyword]]. This means that the method is invoked using a specific instance of the <code>OddEven</code> class. (The [[Reference (computer science)|reference]] used to invoke the method is passed as an undeclared parameter of type <code>OddEven</code> named <code>'''[[this (computer science)|this]]'''</code>.) The method tests the expression <code>userInput % 2 == 0</code> using the <code>'''[[Java keywords#if|if]]'''</code> keyword to see if the remainder of dividing the <code>userInput</code> field belonging to the instance of the class by two is zero. If this expression is true, then it prints '''Even'''; if this expression is false it prints '''Odd'''. (The <code>calculate</code> method can be equivalently accessed as <code>this.calculate</code> and the <code>userInput</code> field can be equivalently accessed as <code>this.userInput</code>, which both explicitly use the undeclared <code>this</code> parameter.)
* <code>'''OddEven number = new OddEven();'''</code> declares a local object [[Reference (computer science)|reference]] variable in the <code>main</code> method named <code>number</code>. This variable can hold a reference to an object of type <code>OddEven</code>. The declaration initializes <code>number</code> by first creating an instance of the <code>OddEven</code> class, using the <code>'''[[List of Java keywords#new|new]]'''</code> keyword and the <code>OddEven()</code> constructor, and then assigning this instance to the variable.
* The statement <code>'''number.showDialog();'''</code> calls the calculate method. The instance of <code>OddEven</code> object referenced by the <code>number</code> [[local variable]] is used to invoke the method and passed as the undeclared <code>this</code> parameter to the <code>calculate</code> method.
* <code>'''userInput = Integer.parseInt(JOptionPane.showInputDialog("Please Enter A Number"));'''</code> is a statement that converts the type of '''String''' to the [[primitive data type]] '''int''' by using a utility function in the [[primitive wrapper class]] '''Integer'''.

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

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

Java applets are programs that are 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> ([[subclass (computer science)|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}} [[superclass (computer science)|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"
"https://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><applet></code>''' [[HTML element]]. The <code>applet</code> tag has three attributes set: '''<code>code="Hello"</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=https://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=https://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 of 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 lang-java"><%</code> and <code lang-java">%></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 [[Mac OS X]]. 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 [[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 of 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 [[GUI widget|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}}''' — 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 a large number of container classes, each containing almost identical code. In addition to enabling more efficient code, certain runtime exceptions are converted to compile-time errors, a characteristic known as [[type safety]].

==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=4 July 2011}}</ref> speed,<ref>{{cite web 
|last=Jelovic |first=Dejan 
|title=Why Java Will Always Be Slower than C++ 
|url=https://www.jelovic.com/articles/why_java_is_slow.htm
|publisher=www.jelovic.com
|accessdate=17 October 2012}}</ref> the handling of unsigned numbers,<ref>{{cite web 
|last=Owens |first=Sean R. 
|url=https://darksleep.com/player/JavaAndUnsignedTypes.html 
|archiveurl=https://web.archive.org/web/20090220171410/https://darksleep.com/player/JavaAndUnsignedTypes.html 
|archivedate=2004-11-09 
|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=https://www.cs.berkeley.edu/~wkahan/JAVAhurt.pdf 
|publisher=Electrical Engineering & Computer Science, University of California at Berkeley 
|accessdate=4 June 2011 }}</ref> and a history of security vulnerabilities in the primary Java VM implementation [[HotSpot]].<ref>{{cite web
|url=https://blogs.technet.com/b/mmpc/archive/2010/10/18/have-you-checked-the-java.aspx
|title=Have you checked the Java?}}
</ref>

==Use on unofficial software platforms==
Java, the programming language, requires the presence of a software platform in order for compiled programs to be executed. One of the official software platforms is the [[Java SE platform]]. A very popular unofficial software platform is the Android software platform, which uses a different bytecode language and virtual machine, and is designed for low-memory devices such as [[smartphones]] and [[Tablet computer|tablets]]. [[File:Android 4.4.2.png|thumb|upright|[[Android (operating system)|Android]] makes extensive use of Java-related technology]]

===Google===
{{See also|Oracle v. Google}}
[[Google]] and Android, Inc. have chosen to use Java as a key pillar in the creation of the [[Android (operating system)|Android operating system]], an [[open-source]] [[smartphone operating system]]. Although the Android operating system, built on the [[Linux kernel]], was written largely in C, the [[Android SDK]] uses the Java language as the basis for Android applications.  However, Android does not use the Java virtual machine, instead using Java bytecode as an intermediate step and ultimately targeting Android's own [[Dalvik (software)|Dalvik virtual machine]].

Android also does not provide the full [[Java SE]] standard library, although the Android class library does include an independent implementation of a large subset of it. This 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=8 May 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 Circuit Court in May 2014.<ref name="cnet appeals">{{cite news | url=https://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><ref name="cafc 13-1021">{{cite web | url=https://www.cafc.uscourts.gov/images/stories/opinions-orders/13-1021.Opinion.5-7-2014.1.PDF | title=ORACLE AMERICA, INC. , Plaintiff - Appellant, v. GOOGLE INC., Defendant - Cross - Appellant. | publisher=Court of Appeals for the Federal Circuit | date=May 9, 2014 | accessdate=2014-05-10}}</ref>

==Class libraries==
{{unreferenced section|date=May 2013}}
<!-- Deleted image removed: [[Image:JavaPlatform.png|350px|thumb|Java Platform and Class libraries diagram]] -->
* The [[Java Class Library]] are the compiled [[bytecode]]s of [[source code]] developed by the JRE implementor to support application development in Java. Examples of these libraries are:
** The core libraries, which include:
*** Many low level, GUI, Integration, Deployment and Tools [https://docs.oracle.com/javase/7/docs/ Java Platform Standard Edition 7 Documentation]
*** [[Java collections framework|Collection libraries]] that implement [[data structure]]s such as [[List (computing)|lists]], [[associative array|dictionaries]], [[tree structure|trees]], [[Set (computer science)|sets]], [[Queue (data structure)|queues]] and [[double-ended queue]], or [[Stack (data structure)|stacks]]
*** [[XML]] Processing (Parsing, Transforming, Validating) libraries
*** Security
*** [[Internationalization and localization]] libraries
** 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 mode|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
* 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. It provides developers with an organized system for documenting their code. [[Javadoc]] comments have an extra asterisk at the beginning, i.e. the tags are /** and */, whereas the normal multi-line comments in Java are set off with the tags /* and */.

==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.
* [[Java Platform, Micro Edition]] (Java ME) — targeting environments with limited resources.
* [[Java Platform, Standard Edition]] (Java SE) — targeting workstation environments.
* [[Java Platform, Enterprise Edition]] (Java EE) — targeting large distributed enterprise or Internet environments.

The [[Class (computer science)|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.

The set of APIs 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.

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]]
* [[JavaOne]]
* [[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

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

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

==References==
{{Refbegin}}
* [[James Gosling|Gosling, James]], [https://duke.dev.java.net/green/ ''A brief history of the Green project''].{{Dead link|date=June 2011}} Java.net, no date [ca. Q1/1998]. Retrieved April 29, 2007.
* [[James Gosling|Gosling, James]], [https://www.anonymous-insider.net/java/research/1998/05-a.html ''A brief history of the Green project''].{{Dead link|date=December 2013}} anonymous-insider.net, no date [ca. Q1/1998]. Retrieved September 4, 2013.
* {{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=https://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=https://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}}
* [https://www.java.com/ java.com]: Main website
{{Java (Sun)}}
{{Sun Microsystems}}
{{FOSS}}

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[[Category:Class-based programming languages]]
[[Category:Concurrent programming languages]]
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[[Category:Java platform|Programming language]]
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[[Category:Java specification requests|Programming language]]
[[Category:JVM programming languages]]
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