In programming, the term Java is used for
a.) a set of libraries, specifications and tools that together form a software development platform.
b.) a programming language for this platform. There are many different languages running on the java platform, and the Java Language is the one that most often used.
wikipedia has more details on this subject:
Java Platform:
Java refers to a number of computer software products and specifications from Sun Microsystems (the Java™ technology) that together provide a system for developing and deploying cross-platform applications. Java is used in a wide variety of computing platforms spanning from embedded devices and cell phones on the low end to enterprise servers and super computers on the high end. Java is fairly ubiquitous in cell phones, Web servers and enterprise applications, and somewhat less common in desktop applications, though users may have come across Java applets when browsing the Web.
For years, Sun Microsystems referred to Java as the "Java technology" but has used the word "Java" as an adjective about the technology. In practice, many programmers have used the word "Java" to mean the programming language, while the execution platform was called the "JRE" (Java Runtime Environment) and the compiler-system was called the "JDK" (Java Development Kit), rather than a "Java compiler" as such. The word "Java" has often been used as an adjective, but the formal term "Java technology" should be noted (see history below).
Java Language:
Java is an object-oriented programming language developed by James Gosling and colleagues at Sun Microsystems in the early 1990s. Unlike conventional languages which are generally either designed to be compiled to native (machine) code, or interpreted from source code at runtime, Java is intended to be compiled to a bytecode (though can be compiled to native code with gcj) which is then run (generally using JIT compilation) by a Java virtual machine.
The language itself borrows much syntax from C and C++ but has a simpler object model and fewer low-level facilities.
Java is only distantly related to JavaScript, though they have similar names and share a C-like syntax.
Java was started as a project called "Oak" by James Gosling in June 1991. Gosling's goals were to implement a virtual machine and a language that had a familiar C-like notation but with greater uniformity and simplicity than C/C++. The first public implementation was Java 1.0 in 1995. It made the promise of "Write Once, Run Anywhere" (WORA), free runtimes on popular platforms. It was fairly secure and its security was configurable, allowing for network and file access to be limited. The major web browsers soon incorporated it into their standard configurations in a secure "applet" configuration. It became popular quickly. New versions for large and small platforms (J2EE and J2ME) soon were designed with the advent of "Java 2". Sun has not announced any plans for a "Java 3".
In 1997, Sun approached the ISO/IEC JTC1 standards body and later the Ecma International to formalize Java, but it soon withdrew from the process.[1][2][3] Java remains a proprietary de facto standard that is controlled through the Java Community Process [4]. Sun makes most of its Java implementations available without charge, with revenue being generated by specialized products such as Java Enterprise System. Sun distinguishes between its Software Development Kit (SDK) and Runtime Environment (JRE) which is a subset of the SDK, the primary distinction being that the compiler is not present.
There were five primary goals in the creation of the Java language:
1. It should use the object-oriented programming methodology.
2. It should allow the same program to be executed on multiple operating systems.
3. It should contain built-in support for using computer networks.
4. It should be designed to execute code from remote sources securely.
5. It should be easy to use by selecting what was considered the good parts of other object-oriented languages.
To achieve the goals of networking support and remote code execution, Java programmers sometimes find it necessary to use extensions such as CORBA, Internet Communications Engine, or OSGi.
The first characteristic, object orientation ("OO"), refers to a method of programming and language design. Although there are many interpretations of OO, one primary distinguishing idea is to design software so that the various types of data it manipulates are combined together with their relevant operations. Thus, data and code are combined into entities called objects. An object can be thought of as a self-contained bundle of behavior (code) and state (data). The principle is to separate the things that change from the things that stay the same; often, a change to some data structure requires a corresponding change to the code that operates on that data, or vice versa. This separation into coherent objects provides a more stable foundation for a software system's design. The intent is to make large software projects easier to manage, thus improving quality and reducing the number of failed projects.
Another primary goal of OO programming is to develop more generic objects so that software can become more reusable between projects. A generic "customer" object, for example, should in theory have roughly the same basic set of behaviors between different software projects, especially when these projects overlap on some fundamental level as they often do in large organizations. In this sense, software objects can hopefully be seen more as pluggable components, helping the software industry build projects largely from existing and well-tested pieces, thus leading to a massive reduction in development times. Software reusability has met with mixed practical results, with two main difficulties: the design of truly generic objects is poorly understood, and a methodology for broad communication of reuse opportunities is lacking. Some open source communities want to help ease the reuse problem, by providing authors with ways to disseminate information about generally reusable objects and object libraries.
'''Java''' is an [[Object-oriented programming|object-oriented]] [[programming language]] developed by [[James Gosling]] and colleagues at [[Sun Microsystems]] in the early 1990s. Unlike conventional languages which are generally either designed to be compiled to native (machine) code, or interpreted from [[source code]] at [[runtime]], Java is intended to be compiled to a [[Byte-code|bytecode]] (though can be compiled to native code with [[gcj]]) which is then run (generally using [[JIT compilation]]) by a [[Java virtual machine]].
The language itself borrows much syntax from [[C programming language|C]] and [[C++]] but has a simpler object model and fewer low-level facilities.
Java is only distantly related to [[JavaScript]], though they have similar names and share a [[C programming language|C]]-like [[Syntax#Syntax in computer science|syntax]].
==History==
Java was started as a project called "Oak" by James Gosling in June 1991. Gosling's goals were to implement a [[virtual machine]] and a language that had a familiar C-like notation but with greater uniformity and simplicity than C/C++. The first public implementation was Java 1.0 in 1995. It made the promise of "[[Write once, run anywhere|Write Once, Run Anywhere]]" (WORA), free runtimes on popular platforms. It was fairly secure and its security was configurable, allowing for network and file access to be limited. The major web browsers soon incorporated it into their standard configurations in a secure "applet" configuration. It became popular quickly. New versions for large and small platforms (J2EE and J2ME) soon were designed with the advent of "Java 2". Sun has not announced any plans for a "Java 3".
In 1997, Sun approached the ISO/IEC JTC1 standards body and later the [[Ecma International]] to formalize Java, but it soon withdrew from the process.
[[http://www.open-std.org/JTC1/SC22/JSG/ Java Study Group]][[http://csdl2.computer.org/comp/proceedings/hicss/2001/0981/05/09815015.pdf Why Java™ Was - Not - Standardized Twice]][[http://techupdate.zdnet.com/techupdate/stories/main/0,14179,2832719,00.html What is ECMA--and why Microsoft cares]] Java remains a proprietary de facto standard that is controlled through the Java Community Process
[[http://www.jcp.org/en/home/index Java Community Process website]]. Sun makes most of its Java implementations available without charge, with revenue being generated by specialized products such as Java Enterprise System. Sun distinguishes between its Software Development Kit (SDK) and [[HotSpot|Runtime Environment (JRE)]] which is a subset of the SDK, the primary distinction being that the compiler is not present.
== Philosophy ==
There were five primary goals in the creation of the Java language:
# It should use the [[object-oriented programming]] methodology.
# It should allow the same program to be executed on multiple operating systems.
# It should contain built-in support for using [[computer network]]s.
# It should be designed to execute code from remote sources securely.
# It should be easy to use by selecting what was considered the good parts of other object-oriented languages.
To achieve the goals of networking support and remote code execution, Java programmers sometimes find it necessary to use extensions such as [[CORBA]], [[Internet Communications Engine]], or [[OSGi]].
=== Object orientation ===
The first characteristic, [[object-oriented programming|object orientation]] ("OO"), refers to a method of programming and language design. Although there are many interpretations of OO, one primary distinguishing idea is to design software so that the various types of data it manipulates are combined together with their relevant operations. Thus, data and code are combined into entities called [[Object (computer science)|objects]]. An object can be thought of as a self-contained bundle of ''behavior'' (code) and ''state'' (data). The principle is to separate the things that change from the things that stay the same; often, a change to some data structure requires a corresponding change to the code that operates on that data, or vice versa. This separation into coherent objects provides a more stable foundation for a software system's design. The intent is to make large software projects easier to manage, thus improving quality and reducing the number of failed projects.
Another primary goal of OO programming is to develop more generic objects so that software can become more reusable between projects. A generic "customer" object, for example, should in theory have roughly the same basic set of behaviors between different software projects, especially when these projects overlap on some fundamental level as they often do in large organizations. In this sense, software objects can hopefully be seen more as pluggable [[software componentry|components]], helping the software industry build projects largely from existing and well-tested pieces, thus leading to a massive reduction in development times. Software reusability has met with mixed practical results, with two main difficulties: the design of truly generic objects is poorly understood, and a methodology for broad communication of reuse opportunities is lacking. Some [[Open source#Innovation communities|open source communities]] want to help ease the reuse problem, by providing authors with ways to disseminate information about generally reusable objects and object libraries.
=== Platform independence ===
[[Image:SwingSet.png|thumb|The [[look and feel]] of Java Swing [[Graphical user interface|GUI]]s is independent of the platform on which they are running]]
The second characteristic, [[Cross-platform|platform independence]], means that [[computer program|program]]s written in the Java language must run similarly on diverse hardware. One should be able to write a program once and run it anywhere.
This is achieved by most Java [[compiler]]s by compiling the Java language code "halfway" to [[bytecode]] (specifically [[Java bytecode]])—simplified machine instructions specific to the Java platform. The code is then run on a [[virtual machine]] (VM), a program written in native code on the host hardware that [[Interpreter (computing)|interprets]] and executes generic Java bytecode. Further, standardized libraries are provided to allow access to features of the host machines (such as graphics, [[thread (computer science)|threading]] and [[Computer network|networking]]) in unified ways. Note that, although there's an explicit compiling stage, at some point, the Java bytecode is interpreted or converted to native [[assembly language|machine instructions]] by the [[Just-in-time compilation|JIT compiler]].
There are also implementations of Java compilers that compile to native [[object code]], such as [[GCJ]], removing the intermediate bytecode stage, but the output of these compilers can only be run on a single [[Computer architecture|architecture]].
Sun's license for Java insists that all implementations be "compatible". This resulted in a legal dispute with Microsoft after Sun claimed that the Microsoft implementation did not support the RMI and JNI interfaces and had added platform-specific features of their own. Sun sued and won both damages (some $20 million) and a court order enforcing the terms of the license from Sun. In response, Microsoft no longer ships Java with Windows, and in recent versions of Windows, Internet Explorer cannot support Java applets without a third-party plugin. However, Sun and others have made available Java run-time systems at no cost for those and other versions of Windows.
The first implementations of the language used an interpreted virtual machine to achieve [[Porting|portability]]. These implementations produced programs that ran more slowly than programs compiled to native executables, for instance written in C or C++, so the language suffered a reputation for poor performance. More recent JVM implementations produce programs that run significantly faster than before, using multiple techniques.
The first technique is to simply compile directly into native code like a more traditional compiler, skipping bytecodes entirely. This achieves good performance, but at the expense of portability. Another technique, known as ''just-in-time compilation'' (JIT), translates the Java bytecodes into native code at the time that the program is run which results in a program that executes faster than interpreted code but also incurs [[compilation overhead]] during execution. More sophisticated VMs use ''[[dynamic recompilation]]'', in which the VM can analyze the behavior of the running program and selectively recompile and optimize critical parts of the program. Dynamic recompilation can achieve optimizations superior to static compilation because the dynamic compiler can base optimizations on knowledge about the runtime environment and the set of loaded classes. JIT compilation and dynamic recompilation allow Java programs to take advantage of the speed of native code without losing portability.
Portability is a technically difficult goal to achieve, and Java's success at that goal has been mixed. Although it is indeed possible to write programs for the Java platform that behave consistently across many host platforms, the large number of available platforms with small errors or inconsistencies led some to parody Sun's "[[Write once, run anywhere]]" slogan as "Write once, [[debug]] everywhere".
Platform-independent Java is however very successful with server-side applications, such as [[Web service]]s, [[servlet]]s, and [[Enterprise JavaBean]]s, as well as with [[Embedded system]]s based on [[OSGi]], using [[Embedded Java]] environments.
=== Automatic garbage collection ===
One idea behind Java's automatic memory management model is that programmers should be spared the burden of having to perform manual [[memory management]]. In some languages the programmer allocates memory to create any object stored on the [[heap (programming)|heap]] and is responsible for later manually deallocating that memory to delete any such objects. If a programmer forgets to deallocate memory or writes code that fails to do so in a timely fashion, a [[memory leak]] can occur: the program will consume a potentially arbitrarily large amount of memory. In addition, if a region of memory is deallocated twice, the program can become unstable and may crash. Finally, in non garbage collected environments, there is a certain degree of overhead and complexity of user-code to track and finalize allocations. Often developers may box themselves into certain designs to provide reasonable assurances that memory leaks will not occur.
In Java, this potential problem is avoided by [[garbage collection (computer science)|automatic garbage collection]]. The programmer determines when objects are created, and the Java runtime is responsible for managing the [[Object lifetime|object's lifecycle]]. The program or other objects can reference an object by holding a reference to it (which, from a low-level point of view, is its address on the heap). When no references to an object remain, the Java garbage collector automatically deletes the [[unreachable object]], freeing memory and preventing a memory leak. Memory leaks may still occur if a programmer's code holds a reference to an object that is no longer needed—in other words, they can still occur but at higher conceptual levels.
The use of garbage collection in a language can also affect programming paradigms. If, for example, the developer assumes that the cost of memory allocation/recollection is low, they may choose to more freely construct objects instead of pre-initializing, holding and reusing them. With the small cost of potential performance penalities (inner-loop construction of large/complex objects), this facilitates thread-isolation (no need to synchronize as different threads work on different object instances) and data-hiding. The use of transient immutable value-objects minimizes side-effect programming.
Comparing Java and [[C++]], it is possible in C++ to implement similar functionality (for example, a memory management model for specific classes can be designed in C++ to improve speed and lower memory fragmentation considerably), with the possible cost of extra development time and some application complexity. In Java, garbage collection is built-in and virtually invisible to the developer. That is, developers may have no notion of when garbage collection will take place as it may not necessarily correlate with any actions being explicitly performed by the code they write. Depending on intended application, this can be beneficial or diadvantageous: the programmer is freed from performing low-level tasks, but at the same time loses the option of writing lower level code.
== Syntax ==
{{Main|Java syntax}}
The syntax of Java is largely derived from C++. However, unlike C++, which combines the syntax for structured, generic, and object-oriented programming, Java was built from the ground up to be virtually fully object-oriented: everything in Java is an object with the exceptions of atomic datatypes (ordinal and real numbers, boolean values, and characters) and everything in Java is written inside a class.
=== Hello world ===
:''For an explanation of the tradition of programming "Hello World" see: [[Hello world program]].''
==== Stand-alone application ====
// Hello.java
public class Hello {
public static void main(String[] args) {
System.out.println("Hello, world!");
}
}
This is a minimal usage of the JVM, but it does not demonstrate object-oriented programmming very well. No object is explicitly created in the above example since the keyword ''new'' is never used. The class "Hello" merely provides a namespace for the static "main" routine. Technically, the object System.out is used, but it is implicitly created by the JVM before the main routine is called.
==== Applet ====
{{Main|Java applet}}
Java applets are programs that are embedded in other applications, typically in a Web page displayed in a [[Web browser]].
// Hello.java
import java.applet.Applet;
import java.awt.Graphics;
public class Hello extends Applet {
public void paint(Graphics gc) {
gc.drawString("Hello, world!", 65, 95);
}
}
This applet will simply draw the string "Hello, world!" in the rectangle within which the applet will run. This is a slightly better example of using Java's OO features in that the class explicitly extends the basic "Applet" class, that it overrides the "paint" method and that it uses
import statements.
Hello World Applet
An applet is placed in an [[HTML]] document using the '''
''' [[HTML element]]. The
applet tag has three attributes set: '''
code="Hello"''' specifies the name of the
Applet class and '''
width="200" height="200"''' sets the pixel width and height of the applet. (Applets may also be embedded in HTML using either the
object or
embed element, although support for these elements by Web browsers is inconsistent.[http://java.sun.com/docs/books/tutorial/deployment/applet/applettag.html][http://java.sun.com/docs/books/tutorial/deployment/applet/mixedbrowser.html])
==== Servlet ====
{{Main|Java Servlet}}
Java servlets are [[server-side]] Java EE components that generate responses to requests from [[client (computing)|client]]s.
// Hello.java
import java.io.*;
import javax.servlet.*;
public class Hello extends GenericServlet {
public void service(ServletRequest request, ServletResponse response)
throws ServletException, IOException
{
response.setContentType("text/html");
PrintWriter pw = response.getWriter();
pw.println("Hello, world!");
pw.close();
}
}
The '''
import''' 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}}''' [[Java package|packages]] in the compilation.
The
'''Hello''' class
'''extends''' the '''{{Javadoc:EE|javax/servlet|GenericServlet}}''' class; the
GenericServlet class provides the interface for the [[server (computing)|server]] to forward requests to the servlet and control the servlet's lifecycle.
The
Hello 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
service() 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
service() method declares that it
'''throws''' 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.
==== Swing application ====
[[Swing (Java)|Swing]] is the advanced graphical user interface [[library (computer science)|library]] for the Java SE platform.
// Hello.java
import javax.swing.*;
public class Hello extends JFrame {
Hello() {
setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
add(new JLabel("Hello, world!"));
pack();
}
public static void main(String[] args) {
new Hello().setVisible(true);
}
}
The '''
import''' statement directs the Java compiler to include all of the public classes and interfaces from the '''{{Javadoc:SE|package=javax.swing|javax/swing}}''' package in the compilation.
The
'''Hello''' class
'''extends''' the '''{{Javadoc:SE|javax/swing|JFrame}}''' class; the
JFrame class implements a [[window (computing)|window]] with a [[title bar]] with a close [[Widget (computing)|control]].
The
'''Hello()''' [[constructor (computer science)|constructor]] initializes the frame by first calling the '''{{Javadoc:SE|name=setDefaultCloseOperation(int)|javax/swing|JFrame|setDefaultCloseOperation(int)}}''' method inherited from
JFrame to set the default operation when the close control on the title bar is selected to
'''{{Javadoc:SE|javax/swing|WindowConstants|DISPOSE_ON_CLOSE}}'''—this causes the
JFrame to be disposed of when the frame is closed (as opposed to merely hidden), which allows the JVM to exit and the program to terminate. Next a '''
new {{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 [[layout]] its contents.
The
'''main()''' method is called by the JVM when the program starts. It [[Instance (programming)|instantiates]] a '''
new Hello''' 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
'''true'''. Note that once the frame is displayed, exiting the
main 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.
== Criticism ==
{{main article|Java criticisms}}
Java was intended to serve as a novel way to manage software complexity. Most consider Java technology to deliver reasonably well on this promise. Java does not universally accommodate all programming styles or environments. See [[Java criticisms]] for a thorough analysis of common criticisms about the language.
===Performance===
Partly due to the early versions of the language, Java has often been perceived as significantly slower, and more memory-consuming, than natively compiled languages such as [[C programming language|C]] or [[C++]]. Performance has increased substantially since then, and relative performance of [[JIT compiler]]s as compared to native compilers has in tests been shown to be quite similar.{{cn}} However, these claims and the performed tests are common subjects of debate and controversy.
===Look and feel===
The default [[look and feel]] of [[Graphical User Interface|GUI]] applications written in Java using the [[Swing (Java)|Swing]] toolkit is very different from native applications. 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 (widget toolkit)|Motif]] are supplied by Sun. [[Apple Computer|Apple]] also provides an [[Aqua (theme)|Aqua]] look and feel for [[Mac OS X]]. Though prior implementations of these look and feels have been considered lacking, Swing in Java SE 6 addresses this problem by using more native [[Widget (computing)|widget]] drawing routines of the underlying platforms. Alternatively, third party toolkits such as [[wx4j]] or [[Standard Widget Toolkit|SWT]] may be used for increased integration with the native windowing system.
===Lack of OO purity===
Java's primitive types are not objects. Primitive types hold their values in the [[Stack-based memory allocation|stack]] rather than being references to values. This was a conscious decision by Java's designers for performance reasons. Because of this, Java is not considered to be a pure object-oriented programming language. However, as of Java 5.0, [[autoboxing]] enables programmers to write as if primitive types are their wrapper classes, and freely interchange between them for improved flexibility.
Java designers decided not to implement certain features present in other OO languages, including:
* multiple inheritance
* operator overloading
* class properties
* tuples
===Single-paradigm language===
Java is predominantly a single-[[programming paradigm|paradigm]] language. However, with the addition of ''static imports'' in Java 5.0 the procedural paradigm is better accommodated than in earlier versions of Java.
== Resources ==
=== Java Runtime Environment ===
The '''[[Java Runtime Environment]]''' or '''JRE''' is the software required to run any [[Application software|application]] deployed on the Java Platform. [[End-user]]s commonly use a JRE in [[software package]]s and Web browser [[plugin]]s. Sun also distributes a superset of the JRE called the Java 2 [[SDK]] (more commonly known as the JDK), which includes development tools such as the Java [[compiler]], [[Javadoc]], and [[debugger]].
==== Components ====
* Java [[Library (computer science)|libraries]] that are the compiled [[byte code]]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:
*** Collection libraries which implement [[data structure]]s such as [[List (computing)|lists]], [[associative array|dictionaries]], [[tree structure|trees]] and [[Set (computer science)|sets]]
*** [[XML]] [[Parsing]] libraries
*** Security
*** [[i18n|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 [[CORBA]] for distributed application development
** [[User Interface]] libraries, which include:
*** The (heavyweight, or [[native mode|native]]) [[Abstract Windowing 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 [[Java virtual machine]] (JVM) which is the means by which the byte codes of the Java libraries and third party applications are executed
* Plugins, which enable [[Java applet|applet]]s to be run in [[Web browser]]s
* [[Java Web Start]], which allows Java applications to be efficiently distributed to [[end user]]s across the [[Internet]]
* Licensing and documentation
=== APIs ===
Sun has defined three platforms targeting different application environments and segmented many of its [[application programming interface|API]]s so that they belong to one of the platforms. The platforms are:
* [[Java Platform, Micro Edition]] (Java ME) — targeting environments with limited resources,
* [[Java Platform, Standard Edition]] (Java SE) — targeting workstation environments, and
* [[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)|interface]]s, 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.
In 2004, IBM and BEA publicly supported the notion of creating an official open source implementation of Java. [[As of 2006]], Sun has agreed that they will eventually open source Java; when and how are still to be defined.
=== Extensions and related architectures ===
The [[Extension (computing)|extensions]] to standard Java are typically in
javax.* packages. They are not included in the JDK or JRE. Extensions and architectures closely tied to the Java programming language include:
* [[Java Platform, Enterprise Edition|Java EE]] (previously J2EE) (Java Platform, Enterprise Edition—for distributed enterprise applications)
* [[Java Platform, Micro Edition|Java ME]] (previously J2ME) (Java Platform, Micro Edition—for PDAs and cellular phones)
* [[JMF]] (Java Media Framework)
* [[JNDI]] (Java Naming and Directory Interface)
* [[JSML]] (Java Speech API Markup Language)
* [[JDBC]] (Java Database Connectivity)
* [[Java Data Objects|JDO]] (Java Data Objects)
* [[Java Advanced Imaging|JAI]] (Java Advanced Imaging)
* [[JAIN]] (Java API for Integrated Networks)
* [[JDMK]] (Java Dynamic Management Kit)
* [[Jini]] (a network architecture for the construction of [[federated]] [[distributed system]]s)
* [[Jiro]]
* [[Java Card]] (Java for [[smart cards]])
* [[JavaSpaces]]
* [[Java Modeling Language|JML]] (Java Modeling Language)
* [[Java Metadata Interface|JMI]] (Java Metadata Interface)
* [[Java Management Extensions|JMX]] (Java Management Extensions)
* [[JavaServer Pages|JSP]] (JavaServer Pages)
* [[JavaServer Faces|JSF]] (JavaServer Faces)
* [[Java Native Interface|JNI]] (Java Native Interface)
* [[JXTA]] (Open Protocols for [[Peer-to-Peer]] (P2P) Virtual Network)
* [[Java 3D]] (A high level API for 3D graphics programming)
* [[Java OpenGL|JOGL]] (Java OpenGL—A low level API for 3D graphics programming, using [[OpenGL]])
* [[Lightweight Java Game Library|LWJGL]] (Light Weight Java Game Library—A low level API providing access to [[OpenGL]], [[OpenAL]] and various input devices)
* [[OSGi]] (Dynamic Service Management and Remote Maintenance)
== See also ==
* [[Java syntax]]
* [[Java keywords]]
* [[Java virtual machine]]
* [[Java platform]]
* [[Java applet]]
* [[Classpath (Java)]]
* [[Java Platform, Standard Edition]] (Java SE, J2SE)
* [[JavaOS]]
* [[Comparison of Java and C++]]
* [[Comparison of C Sharp and Java|Comparison of C# and Java]]
* [[Comparison of programming languages]]
* [[Java User Group]]
* [[Java Community Process]]
* [[JavaOne]]
* [[Join Java|Join Java programming language]]
* [[Javapedia]]
== Books about Java ==
[[Image:Zakhour_java.jpg|thumb|right|The Java Tutorial, Fourth Edition]]
* ''The Java Tutorial, Fourth Edition'', Sharon Zakhour, Addison-Wesley Professional, Sep. 29, 2006. ISBN 0-321-33420-5
=== Lists ===
* [[List of Java scripting languages]]
* [[:Category:Java platform software|Java platform software]]
* [[:Category:Java tools|Java development tools]]
* [[List of Java virtual machines]]
==Notes==
== References ==
* Jon Byous, [http://java.sun.com/features/1998/05/birthday.html ''Java technology: The early years'']. Sun Developer Network, no date [ca. 1998]. Retrieved [[April 22]], [[2005]].
* [[James Gosling]], [http://today.java.net/jag/old/green/ ''A brief history of the Green project'']. Java.net, no date [ca. Q1/1998]. Retrieved [[April 22]], [[2005]].
* [[James Gosling]], [[Bill Joy]], [[Guy L. Steele, Jr.|Guy Steele]], and [[Gilad Bracha]], ''The Java language specification'', third edition. Addison-Wesley, 2005. ISBN 0-321-24678-0 (see also [http://java.sun.com/docs/books/jls/index.html online edition of the specification].
* Tim Lindholm and Frank Yellin. ''The Java Virtual Machine specification'', second edition. Addison-Wesley, 1999. ISBN 0-201-43294-3.
== External links ==
{{Wikibooks|Java Programming}}
=== Sun ===
* [http://java.sun.com/ Official Java home site for IT, developers, etc]
* [http://www.java.com/ Official Java home site non-technical / home-use]
* [http://java.sun.com/docs/books/jls/ The Java Language Specification, Third Edition] Authoritative description of the Java language (also available [http://java.sun.com/docs/books/jls/third_edition/html/j3TOC.html online])
* {{Javadoc:SE}}
* [http://java.sun.com/docs/books/tutorial/ Sun's tutorial on Java Programming]
* [http://java.sun.com/docs/white/langenv/ Original Java whitepaper], 1996
* [http://www.java.com/en/download/help/testvm.xml Test your Java VM]
=== [[Java Specification Request]]s ===
There are several JSRs related to the Java Language and core API packages.
* [http://www.jcp.org/en/jsr/detail?id=14 JSR 14] ''Add [[Generic programming|Generic Types]] To The Java Programming Language'' (J2SE 5.0)
* [http://www.jcp.org/en/jsr/detail?id=41 JSR 41] ''A Simple Assertion Facility'' (J2SE 1.4)
* [http://www.jcp.org/en/jsr/detail?id=47 JSR 47] ''Logging API Specification'' (J2SE 1.4)
* [http://www.jcp.org/en/jsr/detail?id=51 JSR 51] ''[[New I/O]] APIs for the Java Platform'' (J2SE 1.4)
* [http://www.jcp.org/en/jsr/detail?id=59 JSR 59] ''J2SE Merlin Release Contents'' (J2SE 1.4)
* [http://www.jcp.org/en/jsr/detail?id=131 JSR 121] ''[[Application Isolation API]]'' (not yet included)
* [http://www.jcp.org/en/jsr/detail?id=133 JSR 133] ''Java Memory Model and Thread Specification Revision'' (J2SE 5.0)
* [http://www.jcp.org/en/jsr/detail?id=166 JSR 166] ''Concurrency Utilities'' (J2SE 5.0)
* [http://www.jcp.org/en/jsr/detail?id=175 JSR 175] ''[[A Metadata Facility for the Java Programming Language]]'' (J2SE 5.0)
* [http://www.jcp.org/en/jsr/detail?id=176 JSR 176] ''J2SE 5.0 (Tiger) Release Contents'' (J2SE 5.0)
* [http://www.jcp.org/en/jsr/detail?id=201 JSR 201] ''Extending the Java Programming Language with Enumerations, Autoboxing, Enhanced for loops and Static Import'' (J2SE 5.0)
* [http://www.jcp.org/en/jsr/detail?id=203 JSR 203] ''More New I/O APIs for the Java Platform ("NIO.2")'' (Java SE 7)
* [http://www.jcp.org/en/jsr/detail?id=204 JSR 204] ''Unicode Supplementary Character Support'' (J2SE 5.0) – support for [[Unicode]] 3.1
* [http://www.jcp.org/en/jsr/detail?id=270 JSR 270] ''Java SE 6 ("Mustang") Release Contents'' (Java SE 6)
* [http://www.jcp.org/en/jsr/detail?id=275 JSR 275] ''Physical Units/Quantities Support (Java SE) (reference implementation from [[JScience]])
* [http://www.jcp.org/en/jsr/detail?id=901 JSR 901] ''Java Language Specification'' (J2SE 5.0)
=== Resources ===
* [http://www.computer-books.us/java.php Computer-Books.us] A collection of Java books available for free download
* [http://wiki.java.net/bin/view/Javapedia/ Javapedia project]
* [http://wiki.java.net/bin/view/Main/WebHome The Java.net Wiki]
* [http://www.inesystems.com Sun Certification Resource]
* [http://www.javarss.com/ JavaRSS.com] Portal of Java websites
* [http://www.ibm.com/developerworks/java?ca=dgr-wikia-dW-JavaHP developerWorks Java Zone—Java resource community]
* [http://www.javawhat.com/ JavaWhat.com] Java resource directory
* [http://www.codecodex.com/wiki/index.php?title=Category:Java Java at CodeCodex] A wiki collection of Java source code
=== Java Integrated Development Environments ===
The following [[Integrated Development Environment]]s (IDEs) can be used to create Java programs.
* [http://www.bea.com/framework.jsp?CNT=index.htm&FP=/content/products/workshop/ BEA Workshop] – commercial software, developed by [[BEA Systems]], integrates with [[BEA WebLogic]]
* [http://www.bluej.org/ BlueJ] – [[free software]] developed as a joint university research project, [[BlueJ]] is also an interactive development environment suitable for learning Java
* [http://www.drjava.org/ DrJava] free [[open source]] software
* [http://www.eclipse.org/ Eclipse] – free [[open source]] software, [[Eclipse (software)|Eclipse]] is developed by the [[Eclipse Foundation]]
* [http://www.jetbrains.com/idea/ IntelliJ IDEA] – commercial software, [[IntelliJ IDEA]] is developed by [[JetBrains]]
* [http://www.borland.com/us/products/jbuilder/index.html JBuilder] – commercial software (free version available), [[JBuilder]] is developed by [[Borland]]
* [http://www.jcreator.com/ JCreator] – commercial software (free version available), [[JCreator]] is developed by Xinox Software
* [http://www.oracle.com/tools/jdev_home.html JDeveloper] – free software [[JDeveloper]] is developed by [[Oracle Corporation]] and integrates with [[Oracle Application Server]]
* [http://www.netbeans.org/ NetBeans] – free open source software developed by [[NetBeans|NetBeans.org]]
* [http://developers.sun.com/prodtech/javatools/jsenterprise/index.html Sun Java Studio Enterprise] – commercial software (available free to members of the free Sun Developer Network), developed by Sun Microsystems
* [http://www-306.ibm.com/software/websphere/sw-bycategory/subcategory/SW710.html WebSphere Developer & Development Studio] – commercial software, developed by [[IBM]], integrates with [[WebSphere Application Server]]
=== History ===
* [http://java.sun.com/features/1998/05/birthday.html Java™ Technology: The Early Years]
* [http://java.sun.com/people/jag/green/ A Brief History of the Green Project]
* [http://www.cs.umd.edu/users/seanl/stuff/java-objc.html Java Was Strongly Influenced by Objective-C]
* [http://www.wired.com/wired/archive/3.12/java.saga.html The Java Saga]
* [http://java.sun.com/features/2000/06/time-line.html The Java Platform: Five Years in Review]
* [http://ei.cs.vt.edu/~wwwbtb/book/chap1/java_hist.html A history of Java]
=== '''''Java Implementations''''' ===
==== Proprietary ====
* [http://java.sun.com SUN JDK] from [[SUN]]
* [http://www-128.ibm.com/developerworks/java/jdk/ IBM JDK] from [[IBM]]
* [http://www.bea.com/framework.jsp?CNT=index.htm&FP=/content/products/jrockit BEA Systems JRockit] [[JVM]] from [[BEA Systems]]
* [http://www.blackdown.org Blackdown Java] for [[Linux]], includes [[Mozilla]] plugin
==== Open source ====
* [http://www.gnu.org/software/classpath/ GNU Classpath] from [[GNU]] - currently being [[Merge (revision control)|merged]] with libgcj of the [http://gcc.gnu.org/java/ GNU Compiler for Java]
* [http://incubator.apache.org/harmony/ Apache Harmony] (see [[Apache Harmony|Harmony]]) an [[Apache Software Foundation]] proposed implementation of the Java programming language, starting with J2SE 5.0
=== Criticism ===
* [http://www.gnu.org/philosophy/java-trap.html Free But Shackled—The Java Trap], by [[Richard Stallman]], [[April 12]], [[2004]]. ([http://today.java.net/jag/page7.html#59 James Gosling's response])
* [http://www.research.att.com/~bs/bs_faq.html#Java Is Java the language you would have designed if you didn't have to be compatible with C?], by [[Bjarne Stroustrup]]
* [http://www.softpanorama.org/Lang/java.shtml Softpanorama Java Critique Page: Java vs Scripting Languages], by [[Nikolai Bezroukov]]
* [http://www.paulgraham.com/javacover.html Java's Cover] by [[Paul Graham]], April 2001
* [http://www.joelonsoftware.com/articles/ThePerilsofJavaSchools.html The Perils of JavaSchools] by [[Joel Spolsky]] (criticism of the use of Java to teach computer science in college)
* [http://www.cs.berkeley.edu/~wkahan/JAVAhurt.pdf How Java’s Floating-Point Hurts Everyone Everywhere], by [[W. Kahan und Joseph D. Darcy]] at the ''ACM 1998 Workshop on Java for High–Performance Network Computing''
=== Java-like languages ===
* [http://nice.sourceforge.net/ The Nice programming language], a language whose goal is to overcome many of Java's shortcomings while staying true to its Java roots
* For a long list of languages based on Java known to Wikipedia, see: [http://en.wikipedia.org/wiki/Category:Java_programming_language_family Category: Java programming language family]
{{step||[[Mandarax]], [[Nice programming language|Nice]]}}