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What is Java?

Java is an object-oriented programming language developed by James Gosling and colleagues at Sun Microsystems in the early 1990s. The language, which was designed to be platform independent, is a derivative of C++ with a simpler syntax, a more robust runtime environment and simplified memory management.

Java is not related to JavaScript, though they have similar names and share a C-like syntax.

History

Early History
The Java platform and language began as an internal project at Sun Microsystems in December of 1990. Engineer Patrick Naughton had become increasingly frustrated with the state of Sun's C++ and C APIs (application programming interfaces) and tools. While considering moving to NeXT, Naughton was offered a chance to work on new technology and thus the Stealth Project was started.

The Stealth Project was soon renamed to the Green Project with James Gosling and Mike Sheridan joining Naughton. Together with other engineers, they began work in a small office on Sand Hill Road in Menlo Park, California. They were attempting to develop a new technology for programming next generation smart appliances, which Sun expected to be a major new opportunity.

The team originally considered using C++, but it was rejected for several reasons. Because they were developing an embedded system with limited resources, they decided that C++ demanded too large a footprint and that its complexity led to developer errors. The language's lack of garbage collection meant that programmers had to manually manage system memory, a challenging and error-prone task. The team was also troubled by the language's lack of portable facilities for security, distributed programming, and threading. Finally, they wanted a platform that could be easily ported to all types of devices.

Bill Joy had envisioned a new language combining the best of Mesa and C. In a paper called Further, he proposed to Sun that its engineers should produce an object-oriented environment based on C++. Initially, Gosling attempted to modify and extend C++, which he referred to as C++ ++ -- , but soon abandoned that in favor of creating an entirely new language, which he called Oak after the tree that stood just outside his office.

The team worked long hours and by the summer of 1992, they were able to demonstrate portions of the new platform including the Green OS, the Oak language, the libraries, and the hardware. Their first attempt, demonstrated on September 3, 1992, focused on building a PDA device named Star7[1] which had a graphical interface and a smart agent called "Duke" to assist the user. In November of that year, the Green Project was spun off to become FirstPerson, Inc, a wholly owned subsidiary of Sun Microsystems, and the team relocated to Palo Alto. The FirstPerson team was interested in building highly interactive devices, and when Time Warner issued an RFP for a set-top box, FirstPerson changed their target and responded with a proposal for a set-top box platform. However, the cable industry felt that their platform gave too much control to the user and FirstPerson lost their bid to SGI. An additional deal with The 3DO Company for a set-top box also failed to materialize. Unable to generate interest within the TV industry, the company was rolled back into Sun.

Java meets the Internet
In June and July of 1994, after a three-day brainstorming session with John Gage, James Gosling, Joy, Naughton, Wayne Rosing, and Eric Schmidt, the team re-targeted the platform for the Web. They felt that with the advent of the Mosaic browser, the Internet was on its way to evolving into the same highly interactive medium that they had envisioned for cable TV. As a prototype, Naughton wrote a small web browser, WebRunner, later renamed HotJava.

That year, the language was renamed Java after a trademark search revealed that the name "Oak" was used by a manufacturer of video adaptor cards. The name Java was coined at a local coffee shop frequented by some of the members. It is not clear whether the name is an acronym or not; although some accounts claim that it stands for the names of James Gosling, Arthur Van Hoff, and Andy Bechtolsheim, or Just Another Vague Acronym, it is generally accepted that "Java" does not stand for anything. Lending credence to the idea that Java owes its name to the products sold at the coffee shop is the fact that the first 4 bytes (the so-called "Magic number") of any class file are, in hexadecimal, 0xCAFEBABE.

In October of 1994, HotJava and the Java platform was demonstrated for Sun executives. Java 1.0a was made available for download in 1994, but the first public release of Java and the HotJava web browser came on May 23, 1995, at the SunWorld conference. The announcement was made by John Gage, the Director of Science for Sun Microsystems. His announcement was accompanied by a surprise announcement by Marc Andreessen, Executive Vice President of Netscape, that Netscape would be including Java support in its browsers. On January 9th, 1996, the JavaSoft business group was formed by Sun Microsystems to develop the technology.[2] Two weeks later the first version of Java was released.

Recent history
After several years of popularity, Java's place in the browser has steadily eroded. For simple interactive animations, it has been almost completely superseded by Macromedia Flash and Shockwave. As of 2005 its use is mostly limited to more complex applications like Yahoo! Games. It has also suffered from a lack of support by Microsoft which no longer includes the Java platform with Internet Explorer or Windows.

By contrast, on the server side of the Web, Java is far more popular than ever, with many websites using JavaServer Pages and other Java-based technologies.

On the desktop, stand-alone Java applications remain relatively rare because of their large overhead. However, with the great advances in computer power in the last decade along with improvements in VM and compiler quality, several have gained widespread use, including the NetBeans and Eclipse Integrated development environments, and file sharing clients such as Limewire and Azureus. Java is also used in the Matlab mathematics program for rendering the user interface and for part of the calculation functionality. Java Swing desktop applications are being developed as an alternative to Microsoft .NET technology.

Philosophy

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 and borrow the good parts of older object-oriented languages like C++.

Especially for the latter part, however, extensions are sometimes required, like CORBA or OSGi.

Object orientation
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.

Platform independence
The second characteristic, platform independence, means that programs 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 compilers 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 interprets and executes generic Java bytecode. Further, standardized libraries are provided to allow access to features of the host machines (such as graphics, threading and 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 machine instructions by the 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 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 portability. These implementations produced programs that ran more slowly than programs 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. More sophisticated VMs use dynamic recompilation, in which the VM can analyze the behavior of the running program and selectively recompile and optimise 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 services, servlets, and Enterprise Java Beans, as well as with Embedded systems based on OSGi, using Embedded Java environments.

Automatic garbage collection
One possible argument against languages such as C++ is the burden of having to perform manual memory management. In C++, memory is allocated by the programmer to create an object, then deallocated to delete the object. If a programmer forgets or is unsure when to deallocate, this can lead to a memory leak, where a program consumes more and more memory without cleaning up after itself. Even worse, if a region of memory is deallocated twice, the program can become unstable and will likely crash.

In Java, this potential problem is avoided by automatic garbage collection. Objects are created and placed at an address on the heap. The program or other objects can reference an object by holding a reference to its address on the heap. When no references to an object remain, the Java garbage collector automatically deletes the object, freeing memory and preventing a memory leak. Memory leaks, however, can 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. But on the whole, Java's automatic garbage collection makes creation and deletion of objects in Java simpler, potentially safer, and often faster than in C++.

Garbage collection in Java is virtually invisible to the developer. That is, developers may have no notion of when garbage collection will take place as it is not necessarily a function of the code they themselves write.

Criticism

Java was intended to serve as a novel way to manage software complexity. Most consider Java technology to deliver reasonably well on this promise. However, Java is not without flaws, and it does not universally accommodate all programming styles, environments, or requirements.

• Not all projects or environments require enterprise-level complexity, such as stand-alone websites or sole-proprietorship programmers. Such individuals find Java's self-enforcing complexity management to be overkill.
• Java is often a focal point of discontent for those who are not enthusiastic about object-oriented programming.
• Java can be considered a less pure object-oriented programming language than for instance Ruby or Smalltalk because it makes certain compromises (such as the fact that not all values are objects) for performance reasons.
• Java programs may have lower performance than those written in languages such as C++, which are compiled directly into machine code. The reasons for this include the following: Java byte code is not optimized to the same degree as machine code resulting from C++; Java does not support manual inlining (though many JIT compilers perform this optimization); and the usage of a garbage collector to automatically decide when to delete objects is more expensive than imperative deletion in C++ (although modern garbage collectors may outperform imperative deletion).
• As an established technology, Java inevitably invites comparison with contemporary languages such as C++, C#, Python, and others. Commenting upon Java's proprietary nature, supposed inflexibility to change, and growing entrenchment in the corporate sector, some have said that Java is "the new COBOL". Many consider this to be a somewhat hyperbolic assertion, although it does allude to some legitimate concerns with Java's prospects for the future.

Language

• The distinction between reference types and primitive types may be viewed as artificial by programmers who are familiar with languages such as Smalltalk, Python and Ruby, where everything is an object.
• Conversely, C++ programmers can become confused with Java because in Java primitives are always automatic variables and objects always reside on the heap, whereas C++ programmers are explicitly given the choice in both cases by means of operator new.
• Java code is often more verbose than code written in other languages. This is due in part to its frequent type declarations and manual casts. It is also due to the lack of operator overloading (see below) and the relatively simple syntax. However, J2SE 5.0 introduced Generics which addresses the issue of manual casts, as well as new syntax for for-loops which also reduces verbosity.
• Unlike C++, Java does not support user-definable operator overloading; however, this is a deliberate design decision, seen by many as a plus because of the well-known readability and maintenance problems experienced with operator overloading.
• Java is predominantly a single-paradigm language. Historically, it has not been very accommodating of paradigms other than object-oriented programming. As of J2SE 5.0, the procedural paradigm is somewhat better supported in Java with the addition of the ability to import static methods and fields so that they can be used globally as one could do in, for example, C.
• Java only supports single inheritance of implementation. This causes consternation to programmers accustomed to orthogonal multiple inheritance, which is available in many other languages. However, Java employs interfaces, which allow multiple inheritance of type and abstract methods.
• Java's support of text matching and manipulation is not as strong as languages such as Perl or PHP, although regular expressions were introduced in J2SE 1.4.

Library
The look and feel of GUI applications written in Java using the Swing platform is often different from native applications. While programmers can choose to use the AWT toolkit that displays native widgets (and thus look like the operating platform), the AWT toolkit is unable to meet advanced GUI programming needs by wrapping around advanced widgets and not sacrificing portability across the various supported platforms, each of which have vastly different APIs especially for higher-level widgets. The Swing toolkit, written completely in Java, avoids this problem by reimplementing widgets using only the most basic drawing mechanisms that are guaranteed available on all platforms. The drawback is that extra effort is required to resemble the operating platform. While this is possible (using the GTK+ and Windows Look-and-Feel), most users do not know how to change the default Metal Look-And-Feel to one that resembles their native platform, and as a result they are stuck with Java applications that look radically different from their native applications. Of note however, Apple Computer's own optimized version of the Java Runtime, which is included within the Mac OS X distribution, by default implements its "Aqua" Look-And-Feel, giving Swing applications a similar appearance to native Mac software.

Some parts of the standard Java libraries are considered excessively complicated, or badly designed, but cannot be changed due to the need for backward compatibility.

Performance
It is misleading to make any generalization about the performance of Java programs in general, because run-time performance is affected much more by the quality of the compiler or JVM than by any intrinsic properties of the language itself.

Indeed, there are very few language requirements which incur an unavoidable time penalty. Among these are array bounds checking, run-time type checking and virtual function indirection, all of which can be made much cheaper by a good compiler or JVM. Garbage collection may actually increase the performance of some programs, if implemented well.

Relative performance of JIT compilers as compared to native compilers can be quite close (often superseeding native compiled), and is often a subject of debate. The JIT stage may be time-consuming, which is inconvenient for applications that are short-lived and/or contain large amounts of code. Once this is done, however, the performance of the program can easily be comparable to that achieved by a native compiler, even on numerical tasks. In addition, JITs can exploit information from the runtime environment to guide more effective transformations, such as profile-directed inlining.

Java was designed with an emphasis on security and portability, and does not support direct access to the machine architecture and address space. Applications can drop down to native code to access these features using the Java Native Interface (JNI).

About this Tutorial
This tutorial is from The Wikipedia which is published under the GNU Free Documentation License.

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