This article is about the object-oriented programming language. For the software platform, seeJava (software platform). For the Indonesian island, seeJava. For the Indonesian Language, seeJavanese. For other uses, seeJava (disambiguation).
Java gained popularity shortly after its release, and has been a popular programming language since then.[20] Java was the third most popular programming language in 2022[update] according toGitHub.[21] Although still widely popular, there has been a gradual decline in use of Java in recent years withother languages using JVM gaining popularity.[22]
Duke, the Java mascotJames Gosling, the creator of Java, in 2008
James Gosling, Mike Sheridan, andPatrick Naughton initiated the Java language project in June 1991.[23] Java was originally designed for interactive television, but it was too advanced for the digital cable television industry at the time.[24] The language was initially calledOak after anoak tree that stood outside Gosling's office. Later the project went by the nameGreen and was finally renamedJava, fromJava coffee, a type of coffee fromIndonesia.[25] Gosling designed Java with aC/C++-style syntax that system and application programmers would find familiar.[26]
Sun Microsystems released the first public implementation as Java 1.0 in 1996.[27] It promisedwrite once, run anywhere (WORA) functionality, providing no-cost run-times on popularplatforms. Fairly secure and featuring configurable security, it allowed network- and file-access restrictions. Majorweb browsers soon incorporated the ability to runJava applets within web pages, and Java quickly became popular. The Java 1.0 compiler was re-writtenin Java byArthur van Hoff to comply strictly with the Java 1.0 language specification.[28] 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 asJava EE,Java ME, andJava SE, respectively.
In 1997, Sun Microsystems approached theISO/IEC JTC 1 standards body and later theEcma International to formalize Java, but it soon withdrew from the process.[29][30][31] Java remains ade facto standard, controlled through theJava Community Process.[32] At one time, Sun made most of its Java implementations available without charge, despite theirproprietary 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) asfree and open-source software (FOSS), under the terms of theGPL-2.0-only license. On May 8, 2007, Sun finished the process, making all of its JVM's core code available underfree software/open-source distribution terms, aside from a small portion of code to which Sun did not hold the copyright.[33]
Sun's vice-president Rich Green said that Sun's ideal role with regard to Java was as anevangelist.[34] FollowingOracle 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.[35] This did not prevent Oracle from filing a lawsuit against Google shortly after that for using Java inside theAndroid SDK (see theAndroid section).
On April 2, 2010, James Gosling resigned fromOracle.[36]
In January 2016, Oracle announced that Java run-time environments based on JDK 9 will discontinue the browser plugin.[37]
As of November 2024[update], Java 8, 11, 17, and 21 are supported aslong-term support (LTS) versions, with Java 25, releasing in September 2025, as the next scheduled LTS version.[40]
Oracle released the last zero-cost public update for thelegacy versionJava 8 LTS in January 2019 for commercial use, although it will otherwise still support Java 8 with public updates for personal use indefinitely. Other vendors such asAdoptium continue to offer free builds of OpenJDK's long-term support (LTS) versions. These builds may include additional security patches and bug fixes.[41]
Major release versions of Java, along with their release dates:
Sun has defined and supports four editions of Java targeting different application environments and segmented many of itsAPIs so that they belong to one of the platforms. The platforms are:
Theclasses in the Java APIs are organized into separate groups calledpackages. Each package contains a set of relatedinterfaces, classes, subpackages andexceptions.
Sun also provided an edition calledPersonal Java that has been superseded by later, standards-based Java ME configuration-profile pairings.
One design goal of Java isportability, which means that programs written for the Java platform must run similarly on any combination of hardware and operating system with adequate run time support. This is achieved by compiling the Java language code to an intermediate representation calledJava bytecode, instead of directly to architecture-specificmachine code. Java bytecode instructions are analogous to machine code, but they are intended to be executed by avirtual machine (VM) written specifically for the host hardware.End-users commonly use aJava Runtime Environment (JRE) installed on their device for standalone Java applications or a web browser forJava applets.
Standard libraries provide a generic way to access host-specific features such as graphics,threading, andnetworking.
The use of universal bytecode makes porting simple. However, the overhead ofinterpreting bytecode into machine instructions made interpreted programs almost always run more slowly than nativeexecutables.Just-in-time (JIT) compilers that compile byte-codes to machine code during runtime were introduced from an early stage. Java's Hotspot compiler is actually two compilers in one; and withGraalVM (included in e.g. Java 11, but removed as of Java 16) allowingtiered compilation.[51] Java itself is platform-independent and is adapted to the particular platform it is to run on by aJava virtual machine (JVM), which translates theJava bytecode into the platform's machine language.[52]
Programs written in Java have a reputation for being slower and requiring more memory than those written inC++.[53][54] However, Java programs' execution speed improved significantly with the introduction ofjust-in-time compilation in 1997/1998 forJava 1.1,[55] 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 asHotSpot becoming Sun's default JVM in 2000. With Java 1.5, the performance was improved with the addition of thejava.util.concurrent package, includinglock-free implementations of theConcurrentMaps and other multi-core collections, and it was improved further with Java 1.6.
Non-JVM
Some platforms offer direct hardware support for Java; there are micro controllers that can run Java bytecode in hardware instead of a software Java virtual machine,[56] and someARM-based processors could have hardware support for executing Java bytecode through theirJazelle option, though support has mostly been dropped in current implementations of ARM.
Automatic memory management
Java uses anautomatic garbage collector to manage memory in theobject 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, theunreachable memory becomes eligible to be freed automatically by the garbage collector. Something similar to amemory 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.[57] If methods for a non-existent object are called, anull pointer exception is thrown.[58][59]
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 thestack or explicitly allocated and deallocated from theheap. In the latter case, the responsibility of managing memory resides with the programmer. If the program does not deallocate an object, amemory leak occurs.[57] 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 ofsmart pointers, but these add overhead and complexity. Garbage collection does not preventlogical memory leaks, i.e. those where the memory is still referenced but never used.[57]
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++ stylepointer arithmetic,[60] where object addresses can be arithmetically manipulated (e.g. by adding or subtracting an offset). 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'sprimitive data types are either stored directly in fields (for objects) or on thestack (for methods) rather than on the heap, as is commonly true for non-primitive data types (but seeescape analysis). This was a conscious decision by Java's designers for performance reasons.
Java contains multiple types of garbage collectors. Since Java 9, HotSpot uses theGarbage First Garbage Collector (G1GC) as the default.[61] However, there are also several other garbage collectors that can be used to manage the heap, such as the Z Garbage Collector (ZGC) introduced in Java 11, and Shenandoah GC, introduced in Java 12 but unavailable in Oracle-produced OpenJDK builds. Shenandoah is instead available in third-party builds of OpenJDK, such asEclipse Temurin. For most applications in Java, G1GC is sufficient. In prior versions of Java, such as Java 8, theParallel Garbage Collector was used as the default garbage collector.
Having solved the memory management problem does not relieve the programmer of the burden of handling properly other kinds of resources, like network or database connections, file handles, etc., especially in the presence of exceptions.
This dependency graph of the Java Core classes was created with jdeps andGephi.
The syntax of Java is largely influenced byC++ andC. Unlike C++, which combines the syntax for structured, generic, and object-oriented programming, Java was built almost exclusively as an object-oriented language.[19] 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 values, and characters), which are not objects for performance reasons. Java reuses some popular aspects of C++ (such as theprintf method).
Java usescomments similar to those of C++. There are three different styles of comments: a single line style marked with two slashes (//), a multiple line style opened with/* and closed with*/, and theJavadoc commenting style opened with/** and closed with*/. The Javadoc style of commenting allows the user to run the Javadoc executable to create documentation for the program and can be read by someintegrated development environments (IDEs) such asEclipse to allow developers to access documentation within the IDE.
Java applets were programs embedded in other applications, mainly in web pages displayed in web browsers. The Java applet API was deprecated with the release of Java 9 in 2017.[64][65]
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 areserver-side Java EE components that generate responses to requests fromclients. Most of the time, this means generatingHTML pages in response toHTTP requests, although there are a number of other standard servlet classes available, for example forWebSocket communication.
The Java servlet API has to some extent been superseded (but still used under the hood) by two standard Java technologies for web services:
Typical implementations of these APIs on Application Servers or Servlet Containers use a standard servlet for handling all interactions with theHTTP requests and responses that delegate to the web service methods for the actual business logic.
JavaServer Pages (JSP) areserver-side Java EE components that generate responses, typicallyHTML pages, toHTTP requests fromclients. JSPs embed Java code in an HTML page by using the specialdelimiters<% and%>. A JSP is compiled to a Javaservlet, a Java application in its own right, the first time it is accessed. After that, the generated servlet creates the response.[66]
Swing is a graphical user interfacelibrary for the Java SE platform. It is possible to specify a different look and feel through thepluggable look and feel system of Swing. Clones ofWindows,GTK+, andMotif are supplied by Sun.Apple also provides anAqua look and feel formacOS. Where prior implementations of these looks and feels may have been considered lacking, Swing in Java SE 6 addresses this problem by using more nativeGUI widget drawing routines of the underlying platforms.[67]
In 2004,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, usuallyObject, 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 (ClassCastExceptions) from occurring, it would betype safe.
In 2016, the type system of Java was provenunsound in that it is possible to use generics to construct classes and methods that allow assignment of an instance of one class to a variable of another unrelated class. Such code is accepted by the compiler, but fails at run time with a class cast exception.[70]
Criticisms directed at Java include the implementation of generics,[71] speed,[53] the handling of unsigned numbers,[72] the implementation of floating-point arithmetic,[73] and a history of security vulnerabilities in the primary Java VM implementationHotSpot.[74]Developers have criticized the complexity and verbosity of the Java Persistence API (JPA), a standard part of Java EE. This has led to increased adoption of higher-level abstractions like Spring Data JPA, which aims to simplify database operations and reduce boilerplate code. The growing popularity of such frameworks suggests limitations in the standard JPA implementation's ease-of-use for modern Java development.[75]
TheJava Class Library is thestandard library, developed to support application development in Java. It is controlled byOracle in cooperation with others through theJava Community Process program.[76] Companies or individuals participating in this process can influence the design and development of the APIs. This process has been a subject of controversy during the 2010s.[77] The class library contains features such as:
The (heavyweight, ornative)Abstract Window Toolkit (AWT), which providesGUI components, the means for laying out those components and the means for handling events from those components
The (lightweight)Swing libraries, which are built on AWT but provide (non-native) implementations of the AWT widgetry
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 enableapplets to be run in web browsers
Java Web Start, which allows Java applications to be efficiently distributed toend users across the Internet
Javadoc is a comprehensive documentation system, created bySun Microsystems. 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/** and*/, whereas the normal multi-line comments in Java are delimited by/* and*/, and single-line comments start with//.[85]
Oracle Corporation owns the official implementation of the Java SE platform, due to its acquisition ofSun Microsystems on January 27, 2010. This implementation is based on the original implementation of Java by Sun. The Oracle implementation is available forWindows,macOS,Linux, andSolaris. Because Java lacks any formal standardization recognized byEcma International, ISO/IEC, ANSI, or other third-party standards organizations, the Oracle implementation is thede 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 theJava Development Kit (JDK), which is intended for software developers and includes development tools such as theJava compiler,Javadoc,Jar, and adebugger. Oracle has also releasedGraalVM, a high performance Java dynamic compiler and interpreter.
OpenJDK is another 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 becompatible. This resulted in a legal dispute withMicrosoft after Sun claimed that the Microsoft implementation did not supportJava remote method invocation (RMI) orJava 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.[86] As a result, Microsoft no longer ships Java withWindows.
Platform-independent Java is essential toJava EE, and an even more rigorous validation is required to certify an implementation. This environment enables portable server-side applications.
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 theJava platform for use with Java. TheAndroid SDK is an alternative software platform, used primarily for developingAndroid applications with its own GUI system.
Android
The Java language is a key pillar inAndroid, anopen sourcemobile operating system. Although Android, built on theLinux kernel, is written largely in C, theAndroid SDK uses the Java language as the basis for Android applications but does not use any of its standard GUI, SE, ME or other established Java standards.[87] 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 assmartphones andtablet computers. Depending on the Android version, the bytecode is either interpreted by theDalvik virtual machine or compiled into native code by theAndroid 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).
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.[88] District JudgeWilliam Alsup ruled on May 31, 2012, that APIs cannot be copyrighted,[89] but this was reversed by the United States Court of Appeals for the Federal Circuit in May 2014.[90] 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.[91] In March 2018, this ruling was overturned by the Appeals Court, which sent down the case of determining the damages to federal court in San Francisco.[92]Google filed a petition forwrit of certiorari with theSupreme Court of the United States in January 2019 to challenge the two rulings that were made by the Appeals Court in Oracle's favor.[93] On April 5, 2021, the Court ruled 6–2 in Google's favor, that its use of Java APIs should be consideredfair use. However, the court refused to rule on the copyrightability of APIs, choosing instead to determine their ruling by considering Java's API copyrightable "purely for argument's sake."[94]
^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:Filippova, Elena (September 22, 2005)."Niklaus Wirth's lecture at the Polytechnic Museum in Moscow".Archived from the original on December 1, 2020. RetrievedNovember 20, 2011.), 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 – all these key overall design features are shared by Java and Oberon.
^Patrick Naughton citesObjective-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'sprotocol) and primitive wrapper classes.[3]Archived July 13, 2011, at theWayback Machine
^TechMetrix Research (1999)."History of Java"(PDF).Java Application Servers Report. Archived fromthe original(PDF) on December 29, 2010.The project went ahead under the namegreen and the language was based on an old model ofUCSD Pascal, which makes it possible to generate interpretive code.
^The Java Language Team.About Microsoft's 'Delegates' (White Paper). JavaSoft, Sun Microsystems, Inc. Archived fromthe original on June 27, 2012.In the summer of 1996, Sun was designing the precursor to what is now the event model of the AWT and the JavaBeans 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.
^"Oracle and Java".oracle.com. Oracle Corporation. Archived fromthe original on January 31, 2010. RetrievedAugust 23, 2010.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.
^Salcic, Zoran; Park, Heejong; Teich, Jürgen; Malik, Avinash; Nadeem, Muhammad (July 22, 2017). "Noc-HMP: A Heterogeneous Multicore Processor for Embedded Systems Designed in SystemJ".ACM Transactions on Design Automation of Electronic Systems.22 (4): 73.doi:10.1145/3073416.ISSN1084-4309.S2CID11150290.
^abcBloch 2018, p. 26-28, §Item 7: Eliminate obsolete object references.
^Walter, A. (2010). Towards Certification of Java Applications for Safety Critical Projects.Proceedings of Embedded Real-Time Software and Systems, ERTS2, 1-7.
^van Gurp, Jilles (November 13, 2007)."Google Android: Initial Impressions and Criticism".Javalobby. Archived from the original on August 28, 2008. RetrievedMarch 7, 2009.Frankly, I don't understand why Google intends to ignore the vast amount of existing implementation out there. It seems like a bad case of "not invented here" to me. Ultimately, this will slow adoption. There are already too many Java platforms for the mobile world and this is yet another one
Gosling, James; Joy, Bill; Steele, Guy; Bracha, Gilad; Buckley, Alex (2014).The Java® Language Specification(PDF) (Java SE 8 ed.).Archived(PDF) from the original on October 21, 2014. RetrievedNovember 18, 2014.
_waving.svg)
