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Java (programming language)
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{{Use mdy dates|date=August 2017}}{{short description|Object-oriented programming language}}{{About|a programming language|the software platform|Java (software platform)|the software package downloaded from java.com|Java Platform, Standard Edition}}{{Distinguish|JavaScript}}







factoids
| designer = James Gosling| developer = Oracle Corporationtype system>Static, strong, safe, nominal type system, manifest typing>manifestOpenJDK (javac, sjavac), GNU Compiler for Java (GCJ), Eclipse Compiler for Java (ECJ)Virtual machines: OpenJDK JRE, JRockit>Oracle JRockit, Azul Systems, OpenJ9>IBM J9, Excelsior JET, Gluon VM, Microsoft Java Virtual Machine, Apache HarmonyJIT compilers: HotSpot, GraalVM, Azul Systems>Azul Falcon (LLVM)Ada (programming language)>Ada 83, C++,{{GOOGLE BOOKS>0RUTBAAAQBAJKEYWORDS=PLAINURL=YES, first=Harry H.accessdate=2016-05-29C Sharp (programming language)>C#,Java 5.0 added several new language features (the foreach loop, object type (object-oriented programming)#Autoboxing>autoboxing, variadic function and Java annotation>annotations), after they were introduced in the similar (and competing) C Sharp (programming language) language. weblink {{Webarchive>url=https://web.archive.org/web/20110319065438weblinkweblink {{Webarchive>url=https://web.archive.org/web/20060107162045weblinkEiffel (programming language)>Eiffel,GOSLING, JAMES>AUTHOR2=MCGILTON, HENRYDATE=MAY 1996ACCESS-DATE=MAY 6, 2014ARCHIVE-DATE=MAY 6, 2014DF=MDY-ALL, Mesa (programming language),GOSLING, JAMESAUTHOR3=STEELE, GUYTITLE=THE JAVA LANGUAGE SPECIFICATION, 2ND EDITIONACCESS-DATE=FEBRUARY 8, 2008ARCHIVE-DATE=AUGUST 21, 2011 DF=MDY-ALL, Modula-3,HTTP://WWW.COMPUTERWORLD.COM.AU/INDEX.PHP/ID;1422447371;PP;3;FP;4194304;FPID;1>TITLE=THE A-Z OF PROGRAMMING LANGUAGES: MODULA-3ACCESSDATE=2010-06-09ARCHIVEURL=HTTPS://WEB.ARCHIVE.ORG/WEB/20090105145818/HTTP://WWW.COMPUTERWORLD.COM.AU/INDEX.PHP/ID%3B1422447371%3BPP%3B3%3BFP%3B4194304%3BFPID%3B1DF=MDY-ALL, Oberon (programming language),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, ELENADATE=SEPTEMBER 22, 2005Objective-C,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. weblink {{Webarchiveweblink>date=July 13, 2011}} UCSD Pascal,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.WORK=JAVA APPLICATION SERVERS REPORTYEAR=1999ARCHIVEURL=HTTPS://WEB.ARCHIVE.ORG/WEB/20101229090912/HTTP://WWW.FSCRIPT.ORG/PROF/JAVAPASSPORT.PDFDF=MDY-ALL, HTTP://QUEUE.ACM.ORG/DETAIL.CFM?ID=1017013>TITLE=A CONVERSATION WITH JAMES GOSLING – ACM QUEUE DATE=AUGUST 31, 2004ARCHIVE-URL=HTTPS://WEB.ARCHIVE.ORG/WEB/20150716194245/HTTP://QUEUE.ACM.ORG/DETAIL.CFM?ID=1017013DEAD-URL=NO, mdy-all, Object PascalIn 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.weblink" title="web.archive.org/web/20120627043929weblink">White Paper About Microsoft's DelegatesAda (programming language)>Ada 2005, BeanShell, C Sharp (programming language), Chapel (programming language)>Chapel,CHAPEL SPEC (ACKNOWLEDGEMENTS)>URL=HTTP://CHAPEL.CRAY.COM/SPEC/SPEC-0.98.PDFACCESSDATE=2016-01-14ARCHIVE-URL=HTTPS://WEB.ARCHIVE.ORG/WEB/20160205114946/HTTP://CHAPEL.CRAY.COM/SPEC/SPEC-0.98.PDFDEAD-URL=NOClojure, ECMAScript, Fantom (programming language)>Fantom, Gambas,HTTP://GAMBASWIKI.ORG/WIKI/DOC/INTRO?NH&L=EN>TITLE=GAMBAS DOCUMENTATION INTRODUCTIONACCESSDATE=2017-10-09ARCHIVE-DATE=OCTOBER 9, 2017DF=MDY-ALL, Groovy (programming language), Hack (programming language)>Hack,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 WORLDDATE=MARCH 26, 2014ARCHIVE-URL=HTTPS://WEB.ARCHIVE.ORG/WEB/20150213220946/HTTP://WWW.INFOWORLD.COM/ARTICLE/2610885/FACEBOOK-Q-A--HACK-BRINGS-STATIC-TYPING-TO-PHP-WORLD.HTMLDEAD-URL=NOHaxe (programming language)>Haxe, J Sharp, Kotlin (programming language)>Kotlin, PHP, Python (programming language), Scala (programming language)>Scala, Seed7, Valaoracle.com/java/}}Java class file>.class, .jar| wikibooks = Java Programming}}Java is a general-purpose programming language that is class-based, object-oriented{{sfn|DECODER|||||p=1}} (although not a pure OO language, as it contains primitive typesWEB,weblink Java is pure object oriented or not?, Stack Overflow, 2019-05-24, ), and designed to have as few implementation dependencies as possible. It is intended to let application developers write once, run anywhere (WORA),WEB,weblink Write once, run anywhere?, May 2, 2002, Computer Weekly, 2009-07-27, meaning that compiled Java code can run on all platforms that support Java without the need for recompilation.WEB,weblink 1.2 Design Goals of the Javaâ„¢ Programming Language, Oracle, January 1, 1999, 2013-01-14,weblink" title="web.archive.org/web/20130123204103weblink">weblink January 23, 2013, no, mdy-all, Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of the underlying computer architecture. The syntax of Java is similar to C and C++, but it has fewer low-level facilities than either of them. {{as of|2018}}, Java was one of the most popular programming languages in use according to GitHub,WEB,weblink Is Java Losing Its Mojo?, 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., Robert, McMillan, August 1, 2013, wired.com, March 8, 2017,weblink February 15, 2017, no, mdy-all, weblink particularly for client-server web applications, with a reported 9 million developers.WEB,weblink JavaOne 2013 Review: Java Takes on the Internet of Things, www.oracle.com, 2016-06-19,weblink April 19, 2016, no, mdy-all, Java was originally developed by James Gosling at Sun Microsystems (which has since been acquired by Oracle) and released in 1995 as a core component of Sun Microsystems' Java platform. The original and reference implementation Java compilers, virtual machines, and 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 had relicensed most of its Java technologies under the GNU General Public License. Meanwhile, others have 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 versions are Java 12, released in March 2019, and Java 11, a currently supported long-term support (LTS) version, released on September 25, 2018; Oracle released for the legacy Java 8 LTS the last free public update in January 2019 for commercial use, while it will otherwise still support Java 8 with public updates for personal use up to at least December 2020. Oracle (and others) highly recommend that you uninstall older versions of Java,WEB,weblink Why should I uninstall older versions of Java from my system?, www.java.com, February 6, 2018,weblink February 12, 2018, no, mdy-all, because of serious risks due to unresolved security issues.WEB,weblink Why should I uninstall older versions of Java from my system?, Oracle, 2016-09-09, Since Java 9 (and 10) is no longer supported, Oracle advises its users to immediately transition to Java 11 (Java 12 is also an non-LTS option).

History

{{See also|Java (software platform)#History}}(File:Duke (Java mascot) waving.svg|thumb|upright=0.5|Duke, the Java mascot)File:James Gosling 2008.jpg|thumb|James GoslingJames GoslingFile:Tiobeindex.png|thumb|The TIOBE programming language popularity index graph from 2002 to 2018. Java is steadily on the top since mid-2015.]]James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991.WEB,weblink Java technology: The early years, Byous, Jon, c. 1998, Sun Developer Network, Sun Microsystems, 2005-04-22,weblink" title="web.archive.org/web/20050420081440weblink">weblink April 20, 2005, Java was originally designed for interactive television, but it was too advanced for the digital cable television industry at the time.Object-oriented programming WEB,weblink The History of Java Technology, c. 1995, Sun Developer Network, 2010-04-30,weblink" title="web.archive.org/web/20100210225651weblink">weblink February 10, 2010, no, mdy-all, The language was initially called 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."So why did they decide to call it Java? {{Webarchive|url=https://web.archive.org/web/20131115113216weblink |date=November 15, 2013 }}", Kieron Murphy, JavaWorld.com, 10/04/96 Gosling designed Java with a C/C++-style syntax that system and application programmers would find familiar.Kabutz, Heinz; Once Upon an Oak {{Webarchive|url=https://web.archive.org/web/20070413072630weblink |date=April 13, 2007 }}. Artima. Retrieved April 29, 2007.Sun Microsystems released the first public implementation as Java 1.0 in 1996.WEB,weblink" title="web.archive.org/web/20070310235103weblink">weblink JAVASOFT SHIPS JAVA 1.0, 2018-05-13, It promised ‘Write Once, Run Anywhere’ (WORA), providing no-cost run-times on popular platforms. Fairly secure and featuring configurable security, it allowed network- and file-access restrictions. Major web browsers soon incorporated the ability to run Java applets within web pages, and Java quickly became popular. The Java 1.0 compiler was re-written in Java by Arthur van Hoff to comply strictly with the Java 1.0 language specification.BOOK, {{Google books, rXGMFYXFDwMC, yes, | title= Object-oriented Programming with Java: Essentials and Applications | publisher=Tata McGraw-Hill Education | page=34}} With the advent of Java 2 (released initially as J2SE 1.2 in December 1998{{snd}} 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 EE, Java ME, and 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.WEB,weblink JSG – Java Study Group, open-std.org, August 2, 2006,weblink" title="web.archive.org/web/20060825082008weblink">weblink August 25, 2006, no, mdy-all, WEB,weblink Why Javaâ„¢ Was – Not – Standardized Twice, June 3, 2018,weblink" title="web.archive.org/web/20140113101235weblink">weblink January 13, 2014, no, mdy-all, WEB,weblink What is ECMA—and why Microsoft cares, May 6, 2014,weblink" title="web.archive.org/web/20140506215226weblink">weblink May 6, 2014, no, mdy-all, Java remains a de facto standard, controlled through the Java Community Process.WEB,weblink Java Community Process website, Jcp.org, May 24, 2010, 2010-06-09,weblink" title="web.archive.org/web/20060808070528weblink">weblink August 8, 2006, no, mdy-all, 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.WEB,weblink JAVAONE: Sun – The bulk of Java is open sourced, GrnLight.net, 2014-05-26,weblink" title="web.archive.org/web/20140527220942weblink">weblink May 27, 2014, no, mdy-all, Sun's vice-president Rich Green said that Sun's ideal role with regard to Java was as an evangelist.WEB
,weblink
, Sun's Evolving Role as Java Evangelist
, O'Reilly Media
, August 2, 2009
,weblink" title="web.archive.org/web/20100915162748weblink">weblink
, September 15, 2010
, no
, mdy-all
, Following Oracle Corporation's acquisition of Sun Micro-systems 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.WEB
,weblink
, Oracle and Java
, oracle.com
, Oracle Corporation
, 2010-08-23
, 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.
, bot: unknown
,weblink" title="web.archive.org/web/20100131091008weblink">weblink
, January 31, 2010
,
, 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 centers, game consoles to scientific supercomputers.WEB, Learn About Java Technology,weblink Oracle, November 21, 2011,weblink" title="web.archive.org/web/20111124090716weblink">weblink November 24, 2011, no, mdy-all, On April 2, 2010, James Gosling resigned from Oracle.WEB,weblink Time to move on..., Gosling, James, April 9, 2010, On a New Road, 2011-11-16, James Gosling, bot: unknown,weblink" title="web.archive.org/web/20101105031239weblink">weblink November 5, 2010, In January 2016, Oracle announced that Java run-time environments based on JDK 9 will discontinue the browser plugin.WEB,weblink Moving to a Plugin-Free Web, Dalibor, Topic, March 15, 2016,weblink March 16, 2016, no, mdy-all,

Principles

There were five primary goals in the creation of the Java language:
  1. It must be simple, object-oriented, and familiar.
  2. It must be robust and secure.
  3. It must be architecture-neutral and portable.
  4. It must execute with high performance.
  5. It must be interpreted, threaded, and dynamic.

Versions

{{As of|2019|03}}, Java 8 is supported; and both Java 8 and 11 as Long Term Support (LTS) versions. Major release versions of Java, along with their release dates:
  • JDK 1.0 (January 23, 1996)WEB,weblink JAVASOFT SHIPS JAVA 1.0, 2008-02-05, yes,weblink" title="web.archive.org/web/20070310235103weblink">weblink March 10, 2007,
  • 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)
  • Java SE 10 (March 20, 2018)
  • Java SE 11 (September 25, 2018)WEB,weblink Introducing Java SE 11, Sharat, Chander, oracle.com, September 26, 2018,weblink September 26, 2018, no, mdy-all,
  • Java SE 12 (March 19, 2019)

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 APIs so that they belong to one of the platforms. The platforms are:
  • Java Card for smart-cards.WEB,weblink Java Card Overview, Oracle, Oracle Technology Network, December 18, 2014,weblink" title="web.archive.org/web/20150107034738weblink">weblink January 7, 2015, no, mdy-all,
  • Java Platform, Micro Edition (Java ME) – targeting environments with limited resources.WEB,weblink Java Platform, Micro Edition (Java ME), Oracle, Oracle Technology Network, December 18, 2014,weblink" title="web.archive.org/web/20150104210546weblink">weblink January 4, 2015, no, mdy-all,
  • Java Platform, Standard Edition (Java SE) – targeting workstation environments.WEB,weblink Java SE, Oracle, Oracle Technology Network, December 18, 2014,weblink" title="web.archive.org/web/20141224184532weblink">weblink December 24, 2014, no, mdy-all,
  • Java Platform, Enterprise Edition (Java EE) – targeting large distributed enterprise or Internet environments.WEB,weblink Java Platform, Enterprise Edition (Java EE), Oracle, Oracle Technology Network, December 18, 2014,weblink" title="web.archive.org/web/20141217155326weblink">weblink December 17, 2014, no, mdy-all,
The classes in the Java APIs are organized into separate groups called packages. Each package contains a set of related interfaces, classes, and exceptions. Refer to the separate platforms for a description of the packages available. {{off topic paragraph}}Sun also provided an edition called Personal Java that has been superseded by later, standards-based Java ME configuration-profile pairings.

Execution System

Java JVM and Bytecode

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 run time 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 users commonly use a Java Runtime Environment (JRE) installed on their own machine for standalone Java applications, or in a web browser for Java applets.Standard libraries provide a generic way to access host-specific features such as graphics, threading, and 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 executables. Just-in-time (JIT) compilers that compile byte-codes 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.WEB,weblink 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?, Programmer Interview, 2015-01-19,weblink" title="web.archive.org/web/20150119144223weblink">weblink January 19, 2015, no, mdy-all,

Performance

Programs written in Java have a reputation for being slower and requiring more memory than those written in C++.WEB,weblink Why Java will always be slower than C++, Jelovic, Dejan, 2008-02-15, yes,weblink" title="web.archive.org/web/20080211111923weblink">weblink February 11, 2008, mdy-all, WEB,weblink Loop Recognition in C++/Java/Go/Scala, Google, 2012-07-12, However, Java programs' execution speed improved significantly with the introduction of just-in-time compilation in 1997/1998 for Java 1.1,WEB,weblink Symantec's Just-In-Time Java Compiler To Be Integrated into Sun JDK 1.1, August 1, 2009,weblink" title="web.archive.org/web/20100628171748weblink">weblink June 28, 2010, no, mdy-all, 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 ConcurrentMaps 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,JOURNAL, Salcic, Zoran, Park, Heejong, Teich, Jürgen, Malik, Avinash, Nadeem, Muhammad, 2017-07-22, Noc-HMP: A Heterogeneous Multicore Processor for Embedded Systems Designed in SystemJ,weblink ACM Transactions on Design Automation of Electronic Systems (TODAES), 22, 4, 73, 10.1145/3073416, 1084-4309, and some 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 automatic garbage collector to manage memory in the 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 non-existent object are called, a null pointer exception is thrown.WEB,weblink NullPointerException, Oracle, 2014-05-06,weblink" title="web.archive.org/web/20140506214735weblink">weblink May 6, 2014, no, mdy-all, WEB,weblink Exceptions in Java, Artima.com, 2010-08-10,weblink" title="web.archive.org/web/20090121152332weblink">weblink January 21, 2009, no, mdy-all, 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 or explicitly allocated and deallocated from the 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 pointers, 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 arithmetic, 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's primitive data types are either stored directly in fields (for objects) or on the 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.WEB,weblink Java HotSpotâ„¢ Virtual Machine Performance Enhancements, Oracle.com, 2017-04-26,weblink" title="web.archive.org/web/20170529071720weblink">weblink May 29, 2017, no, mdy-all, 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 (CMS) garbage collector is sufficient.WEB,weblink Java HotSpot VM Options, Oracle.com, 2010-09-07, 2012-06-30,weblink" title="web.archive.org/web/20110306144553weblink">weblink March 6, 2011, no, mdy-all, Oracle aims to replace CMS with the Garbage-First Collector (G1).WEB,weblink Garbage-First Collector, docs.oracle.com, March 15, 2016,weblink" title="web.archive.org/web/20160309234342weblink">weblink March 9, 2016, no, mdy-all, Having solved the memory management problem does not relieve the programmer of the burden of handling properly other kind of resources, like network or database connections, file handles, etc., especially in the presence of exceptions. Paradoxically, the presence of a garbage collector has faded the necessity of having an explicit destructor method in the classes, thus rendering the management of these other resources more difficult.

Syntax

File:JavaUniverse.png|thumb|upright=0.9|Dependency graph of the Java Core classes (created with jdeps and GephiGephiThe 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. 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 the {{java|printf}} method).Unlike C++, Java does not support operator overloadingWEB,weblink Operator Overloading (C# vs Java), Microsoft, C# for Java Developers, December 10, 2014,weblink" title="web.archive.org/web/20150107190007weblink">weblink January 7, 2015, no, mdy-all, or multiple inheritance for classes, though multiple inheritance is supported for interfaces.WEB,weblink Multiple Inheritance of State, Implementation, and Type, Oracle, The Javaâ„¢ Tutorials, December 10, 2014,weblink November 9, 2014, no, mdy-all, Java uses comments 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 the Javadoc 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 some integrated development environments (IDEs) such as Eclipse to allow developers to access documentation within the IDE.

Hello world example

The traditional Hello world program can be written in Java as:WEB,weblink Lesson: A Closer Look at the Hello World Application, The Javaâ„¢ Tutorials > Getting Started, Oracle Corporation, 2011-04-14,weblink" title="web.archive.org/web/20110317072804weblink">weblink March 17, 2011, no, mdy-all, public class HelloWorldApp {
public static void main(String[] args) {
System.out.println("Hello World!"); // Prints the string to the console.
}
}Source files must be named after the public class they contain, appending the suffix .java, for example, HelloWorldApp.java. It must first be compiled into bytecode, using a Java compiler, producing a file named HelloWorldApp.class. 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 modifier and any number of public inner classes. When the source file contains multiple classes, make one class (introduced by the class keyword) public (preceded by the public keyword) and name the source file with that public class name.A class that is not declared public 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 classes are treated as if their name were the concatenation of the name of their enclosing class, a $, and an integer.The keyword public 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 private and protected.The keyword static in front of a method indicates a 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 void 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 main 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 main() method. A Java program may contain multiple classes that have main methods, which means that the VM needs to be explicitly told which class to launch from.The main method must accept an array of {{Javadoc:SE|java/lang|String}} objects. By convention, it is referenced as args although any other legal identifier name can be used. Since Java 5, the main method can also use variable arguments, in the form of public static void main(String... args), allowing the main method to be invoked with an arbitrary number of String arguments. The effect of this alternate declaration is semantically identical (to the args parameter which is still an array of String 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) and starting its public static void main(String[]) method. Stand-alone programs must declare this method explicitly. The String[] args parameter is an array of {{Javadoc:SE|java/lang|String}} objects containing any arguments passed to the class. The parameters to main are often passed by means of a 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 out object is an instance of the {{Javadoc:SE|java/io|PrintStream}} class and provides many methods for printing data to 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.

Example with methods

// 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 memoized = new HashMap();


/*
* 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;
}
}
}

Special classes

{{refimprove|section|date=May 2019}}

Applet

Java applets were programs that were embedded in other applications, typically in a Web page displayed in a web browser. The Java applet API is now deprecated since Java 9 in 2017.WEB,weblink Deprecated APIs, Features, and Options, www.oracle.com, 2019-05-31,

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 HTTP requests) from clients.The Java servlet API has to some extent been superseded by two standard Java technologies for web services:

JavaServer Pages

JavaServer Pages (JSP) are server-side Java EE components that generate responses, typically HTML pages, to HTTP requests from clients. JSPs embed Java code in an HTML page by using the special delimiters . 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

Swing is a graphical user interface 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 Windows, GTK+, and Motif are supplied by Sun. Apple also provides an 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 GUI widget drawing routines of the underlying platforms.

JavaFX application

JavaFX is a software platform for creating and delivering desktop applications, as well as rich Internet applications (RIAs) that can run across a wide variety of devices. JavaFX is intended to replace Swing as the standard GUI library for Java SE, but both will be included for the foreseeable future. JavaFX has support for desktop computers and web browsers on Microsoft Windows, Linux, and macOS. JavaFX does not have support for native OS look and feels.

Generics

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, usually Object, 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 (ClassCastException's) from occurring, it would be type safe.In 2016, the type system of Java was proven unsound.WEB,weblink Java and Scala's Type Systems are Unsound, February 20, 2017,weblink November 28, 2016, no, mdy-all,

Criticism

Criticisms directed at Java include the implementation of generics,WEB
, Arnold
, Ken
, Generics Considered Harmful
,weblink
, java.net
, September 10, 2015
, bot: unknown
,weblink" title="web.archive.org/web/20071010002142weblink">weblink
, October 10, 2007
,
, . More comments to the original article available at earlier archive snapshots like . speed,WEB
, Jelovic
, Dejan
, Why Java Will Always Be Slower than C++
,weblink
, www.jelovic.com
, October 17, 2012
, yes
,weblink" title="web.archive.org/web/20080211111923weblink">weblink
, February 11, 2008
, mdy-all
, the handling of unsigned numbers,OWENS >FIRST=SEAN R.,weblinkweblink" title="web.archive.org/web/20090220171410weblink">weblinktitle=Java and unsigned int, unsigned short, unsigned byte, unsigned long, etc. (Or rather, the lack thereof), 2011-07-04, the implementation of floating-point arithmetic,WEB
, Kahan
, William
, How Java's Floating-Point Hurts Everyone Everywhere
,weblink
, Electrical Engineering & Computer Science, University of California at Berkeley
, June 4, 2011
,weblink
, September 3, 2012
, no
, mdy-all
, and a history of security vulnerabilities in the primary Java VM implementation HotSpot.WEB
,weblink
, Have you checked the Java?
, December 23, 2011
,weblink
, September 3, 2012
, no
, mdy-all
,

Class libraries

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.{{Citation|last=Cadenhead|first=Rogers|title=Understanding How Java Programs Work|date=2017-11-20|url=http://www.informit.com/articles/article.aspx?p=2832404&seqNum=4|access-date=2019-03-26}} 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 2010's.NEWS,weblink Google wins six-year legal battle with Oracle over Android code copyright, Woolf, Nicky, 2016-05-26, The Guardian, 2019-03-26, en-GB, 0261-3077, The class library contains features such as:
  • The core libraries, which include:
  • The integration libraries, which allow the application writer to communicate with external systems. These libraries include:
  • User interface libraries, which include:
    • The (heavyweight, or native) Abstract Window Toolkit (AWT), which provides GUI 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
    • 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 applets to be run in web browsers
  • Java Web Start, which allows Java applications to be efficiently distributed to end users across the Internet
  • Licensing and documentation

Documentation

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 /** and */, whereas the normal multi-line comments in Java are set off with the delimiters /* and */.WEB,weblink How to Write Doc Comments for the Javadoc Tool, Oracle, Oracle Technology Network, December 18, 2014,weblink" title="web.archive.org/web/20141218182906weblink">weblink December 18, 2014, no, mdy-all,

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 are currently officially supported), macOS, Linux, and 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, and a debugger. Oracle has also released GraalVM, a high performance Java dynamic compiler and interpreter.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 RMI or 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.NEWS, Niccolai, James, Sun, Microsoft settle Java lawsuit,weblink JavaWorld, International Data Group, January 23, 2001, 2008-07-09,weblink" title="web.archive.org/web/20080528233154weblink">weblink May 28, 2008, no, mdy-all, As a result, Microsoft no longer ships Java with Windows.Platform-independent Java is essential to Java 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 the Java platform for use with Java. The Android SDK is an alternative software platform, used primarily for developing Android applications with its own GUI system. The Eclipse IDE platform supports Java, but provides its own GUI system SWT.

Android

File:Android 6.0-en.png|thumb|upright|The Android operating system makes extensive use of Java-related technology]]The Java language is a key pillar in Android, an open source mobile operating system. Although Android, built on the Linux kernel, is written largely in C, the 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 smartphones and tablet computers. 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 7 May 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.WEB, Mullin, Joe, Google guilty of infringement in Oracle trial; future legal headaches loom,weblink Law & Disorder, Ars Technica, 2012-05-08,weblink" title="web.archive.org/web/20120508134916weblink">weblink 8 May 2012, no, mdy-all, District Judge William Haskell Alsup ruled on 31 May 2012, that APIs cannot be copyrighted,WEB
, Google wins crucial API ruling, Oracle's case decimated
,weblink
, Joe
, Mullin
, Ars Technica
, 31 May 2012
, 2012-06-01
,weblink
, 12 March 2017
, no
, mdy-all
, but this was reversed by the United States Court of Appeals for the Federal Circuit in May 2014.NEWS,weblink Court sides with Oracle over Android in Java patent appeal, CNET, 9 May 2014, 2014-05-10, Rosenblatt, Seth,weblink" title="web.archive.org/web/20140510203805weblink">weblink 10 May 2014, no, mdy-all, On 26 May 2016, the district court decided in favor of Google, ruling the copyright infringement of the Java API in Android constitutes fair use.WEB, Mullin, Joe, Google beats Oracle—Android makes "fair use" of Java APIs,weblink 2016-05-26, Ars Technica, 2016-05-26,weblink" title="web.archive.org/web/20170120164551weblink">weblink 20 January 2017, no, mdy-all, Google filed a petition for writ of certiorari with the Supreme Court of the United States in January 2019 to challenge the two rulings that were made by the Appeals Court towards Oracle's favor. In its petition, Google centered their case on whether copyright extends to a software interface like an API, and whether the use of the Java API by Google fell within fair use as found at the jury trials.WEB,weblink Google asks Supreme Court to overrule disastrous ruling on API copyrights, Timothy, Lee, April 23, 2019, April 23, 2019, Ars Technica,

See also

{{Wikipedia books|Programming for Students}}

Comparison of Java with other languages

Notes

{{Reflist|30em}}

References

  • BOOK, Gosling, James, Joy, Bill, Steele, Guy, Bracha, Gilad, Buckley, Alex, The Java® Language Specification, 2014, Java SE 8,weblink harv,
  • BOOK, Gosling, James, Joy, Bill, Bill Joy, Steele, Guy L., Jr., Guy L. Steele, Jr., Gilad, Bracha, Gilad Bracha, The Java Language Specification,weblink 3rd, 2005, Addison-Wesley, 0-321-24678-0,
  • BOOK, Lindholm, Tim, Yellin, Frank, The Java Virtual Machine Specification,weblink 2nd, 1999, Addison-Wesley, 0-201-43294-3,

External links

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