毕业论文外文翻译-J2ME和Java领域

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1、原文Java 2 Micro Edition and the World of Java1 Introduction The computer revolution of the 1970s increased the demand for sophisticated computersoftware to take advantage of the ever-increasing capacity of computers to process data.The C programming language became the linchpin that enabled programme

2、rs to buildsoftware that was just as robust as the computer it ran on.As the 1980s approached, programmers were witnessing another spurt in the evolutionof programming language. Computer technology advanced beyond the capabilities of the C programming language. The problem wasnt new. It occurred pre

3、viously and caused the demise of generations of programming languages. The problem was thatprograms were becoming too complicated to design, write, and manage to keep up with the capabilities of computers. It was around this time that a design concept based on Simula 67 and Smalltalk (from the late

4、1960s) moved programming to the next evolutionary step. This was the period when object-oriented programming (OOP), and with it a new programming language called C+, took programmers by storm.In 1979, Bjarne Stroustrup of Bell Laboratories in New Jersey enhanced the C programming language to include

5、 object-oriented features. He called the language C+. (The + is the incremental operator in the C programming language.) C+ is truly an enhancement of the C programming language, and it began as a preprocessor language that was translated into C syntax before the program was processed by the compile

6、r.Stroustrup built on the concept of a class (taken from Simula 67 and Smalltalk), from which instances of objects are created. A class contains data members and member functions that define an objects data and functionality. He also introduced the concept of inheritance, which enabled a class to in

7、herit some or all data members and member functions from one or more other classesall of which complements the concepts of object-oriented programming. By 1988, ANSI officials standardized Stroustrups C+ specification.2 Enter JavaJust as C+ was becoming the language of choice for building industrial

8、-strength applications, another growth spurt in the evolution of programming language was budding, fertilized by the latest disruptive technologythe World Wide Web. The Internet had been a well-kept secret for decades before the National Science Foundation (who oversaw the Internet) removed barriers

9、 that prevented commercialization. Until 1991 when it was opened to commerce, the Internet was the almost exclusive domain of government agencies and the academic community. Once the barrier to commercialization was lifted, the World Wide Webone of several services offered on the Internet became a v

10、irtual community center where visitors could get free information about practically anything and browse through thousands of virtual stores.Browsers power the World Wide Web.A browser translates ASCII text files written in HTML into an interactive display that can be interpreted on any machine. As l

11、ong as the browser is compatible with the correct version of HTML and HTTP implementation, any computer running the browser can use the same HTML document without having to modify it for a particular type of computer, which was something unheard of at the time. Programs written in C or C+ are machin

12、e dependent and cannot run on a differentmachine unless the program is recompiled. The success of the Internet gave renewed focus to developing a machine-independent programming language. And the same year the Internet was commercialized, five technologists at Sun Microsystems set out to do just tha

13、t. James Gosling, Patrick Naughton, ChrisWarth, Ed Frank, and Mike Sheridan spent 18 months developing the programming language they called Oak, which was renamed Java when this new language made its debut in 1995. Java went through numerous iterations between 1991 and 1995, during which time many o

14、ther technologists at Sun made substantial contributions to the language. These included Bill Joy, Arthur van Hoff, Jonathan Payne, Frank Yelin, and Tim Lindholm. Although Java is closely associated with the Internet, it was developed as a language for programming software that could be embedded int

15、o electronic devices regardless of the type of CPU used by the device. This is known as the EmbeddedJava platform and is in continuous use today for closed systems.The Java team from Sun succeeded in creating a portable programming language, something that had eluded programmers since computers were

16、 first programmed. Their success, however, was far beyond their wildest dreams. The same concept used to make Java programs portable to electronic devices also could be used to make Java programs run on computers running Microsoft Windows, UNIX, and Macintosh. Timing was perfect. The Internet/intran

17、et had whetted corporate Americas appetite for cost-effective, portable programs that could replace mission-critical applications within the corporation. And Java had proven itself as a programming language used to successfully develop machine-independent applications.3 Java Virtual MachineWriting J

18、ava programs is similar to writing C+ programs in that the programmer writes source code that contains instructions into an editor, or in an integrated developmentenvironment, and then the source code is compiled. However, thats where Java and C+part ways. The compiling and linking process of a C+ p

19、rogram results in an executablethat can be run on an appropriate machine. In contrast, the Java compiler converts Javasource code into bytecode that is executed by the Java Virtual Machine (JVM).Machine-specific instructions are not included in bytecode. Instead, they already reside in the JVM, whic

20、h is machine specific. This means that the bytecode might contain fewer instructions that need to be translated than a comparable C+ program.A lthough the Java compiler generates bytecode that must be interpreted by the JVMat run time, the number of instructions that need translation are usually min

21、imal andhave already been optimized by the Java compiler.4 Back to the Future: J2MERemember that Java began as a programming language to create programs for embedded systemsmicrocomputers found in consumer and industrial products such as those used to control automobiles and appliances. The developm

22、ent team at Sun worked on Java in the early 1990s to address the programming needs of the fledgling embedded computer market, but that effort was sidetracked by more compelling opportunities presented by the Internet.As those opportunities were addressed, a new breed of portable communications devic

23、es opened other opportunities at the turn of the century. Cell phones expanded J 2 M E : T h e C o m p l e t e R e f e r e n c e from voice communications devices to voice and text communications devices. Pocket electronic telephone directories evolved into personal digital assistants. Chipmakers we

24、re releasing new products at this time that were designed to transfer computing power from a desktop computer into mobile small computers that controlled gas pumps, cable television boxes, and an assortment of other appliances.The time was right for the next evolution of Java. However, instead of be

25、efing up Java with additional APIs, the team at Sun, along with the Java Community Process Program, dismantled both the Java programming language and the Java Virtual Machine. Theystripped down Java APIs and the JVM to the minimum coding required to provideintelligence to embedded systems and microc

26、omputer devices. This was necessarybecause of resource constraints imposed upon the hardware design of these devices. Theresult of their efforts is J2ME. J2ME is a reduced version of the Java API and Java Virtual Machine that is designed to operate within the sparse resources available in the new br

27、eed of embedded computers and microcomputers.5 How J2ME Is Organized Traditional computing devices use fairly standard hardware configurations such as a display, keyboard,mouse, and large amounts of memory and permanent storage. However, the new breed of computing devices lacks hardware configuratio

28、n continuity among devices. Some devices dont have a display, permanent storage, keyboard, or mouse. And memory availability is inconsistent among small computing devices. The lack of uniform hardware configuration among the small computing devices poses a formidable challenge for the Java Community

29、 Process Program, which is charged with developing standards for the JVM and the J2ME for small computing devices. J2ME must service many different kinds of small computing devices, including screenphones, digital set-top boxes used for cable television, cell phones, and personal digital assistants.

30、 The challenge for the Java Community Process Program is to develop a Java standard that can be implemented on small computing devices that have nonstandardhardware configurations. The Java Community Process Program has used a twofold approach to addressing the needs of small computing devices. Firs

31、t, they defined the Java run-time environment and core classes that operate on each device. This is referred to as the configuration. A configuration defines the Java Virtual Machine for a particular small computing device. There are two configurations, one for handheld devices and the other for plu

32、g-in devices. Next, the Java Community Process Program defined a profile for categories of small computing devices. A profile consists of classes that enable developers to implement features found on a related group of small computing devices.6 J2ME configurationsThere are two configurations for J2M

33、E as of this writing. These are Connected Limited Device Configuration (CLDC) and the Connected Device Configuration (CDC). The CLDC is designed for 16-bit or 32-bit small computing devices with limited amounts of memory.CLDC devices usually have between 160KB and 512KB of available memory and are b

34、attery powered. They also use an inconsistent, small-bandwidth network wirelessconnection and may not have a user interface. CLDC devices use the KJava VirtualMachine (KVM) implementation, which is a stripped-down version of the JVM. CLDCdevices include pagers, personal digital assistants, cell phon

35、es, dedicated terminals, andhandheld consumer devices with between 128KB and 512KB of memory.CDC devices use a 32-bit architecture, have at least two megabytes of memoryavailable, and implement a complete functional JVM. CDC devices include digital set-top boxes, home appliances, navigation systems,

36、 point-of-sale terminals, and smart phones.7 J2ME ProfilesA profile consists of Java classes that enable implementation of features for either a particular small computing device or for a class of small computing devices. Small computing technology continues to evolve, and with that, there is an ong

37、oing process of defining J2ME profiles. Seven profiles have been defined as of this writing. These are the Foundation Profile, Game Profile, Mobile Information Device Profile, PDA Profile, Personal Profile, Personal Basis Profile, and RMI Profile. The Foundation Profile is used with the CDC configur

38、ation and is the core for nearly all other profiles used with the CDC configuration because the Foundation Profile contains core Java classes. The Game Profile is also used with the CDC configuration and contains the necessary classes for developing game applications for any small computing device t

39、hat uses the CDC configuration. The Mobile Information Device Profile (MIDP) is used with the CLDC configuration and contains classes that provide local storage, a user interface, and networking capabilities to an application that runs on a mobile computing device such as Palm OS devices. MIDP is us

40、ed with wireless Java applications. The PDAProfile (PDAP) is used with the CLDC configuration and contains classes that utilize sophisticated resources found on personal digital assistants. These features include better displays and larger memory than similar resources found on MIDP mobile devices (

41、such as cell phones). The Personal Profile is used with the CDC configuration and the Foundation Profile and contains classes to implement a complex user interface. The Foundation Profile provides core classes, and the Personal Profiles provide classes to implement a sophisticated user interface, wh

42、ich is a user interface that is capable of displaying multiple windows at a time. The Personal Basis Profile is similar to the Personal Profile in that it is used with the CDC configuration and the Foundation Profile. However, the Personal Basis Profile provides classes to implement a simple user in

43、terface, which is a user interface that is capable of displaying one window at a time. The RMI Profile is used with the CDC configuration and the Foundation Profile to provide Remote Method Invocation classes to the core classes contained in the Foundation Profile.There will likely be many profiles

44、as the proliferation of small computing devices ontinues. Industry groups within the Java Community Process Program ( boutjava/communityprocess) define profiles. Each group establishes the standard rofile used by small computing devices manufactured by that industry.ACDC profile is defined by expand

45、ing upon core Java classes found in the Foundation rofile with classes specifically targeted to a class of small computing device. These device-specific classes are contained in a new profile that enables developers to create ndustrial-strength applications for those devices. However, if the Foundat

46、ion Profile s specific to CDC, not all profiles are expanded upon the core classes found in the oundation Profile. eep in mind that applications can access a small computing devices software and rdware features only if the necessary classes to do so are contained in the JVM and in the profile used b

47、y the developer.8 J2ME and Wireless DevicesWith the dramatic increase and sophistication of mobile communications devices such as cell phones came demand for applications that can run on those devices. Consumers andcorporations want to expand mobile communications devices from voice communicationsto

48、 applications traditionally found on laptops and PCs. They want to send and receiveemail, store and retrieve personal information, perform sophisticated calculations, andplay games.Developers, mobile communications device manufacturers, and mobile networkp roviders are anxious to fill this need, but

49、 there is a serious hurdle: mobile communications devices utilize a number of different application platforms and operating systems.Without tweaking the code, an application written for one device cannot run on another device.Mobile communications devices lack a standard application platform and ope

50、ratingsystem, which has made developing applications for mobile communications devicesa risky economic venture for developers.The lack of standards is nothing new to computing or to any developing technology.Traditionally, manufacturers of hardware devices try to corner the market and enforce their

51、own proprietary standard as the de facto standard for the industry. Usually one upstart succeeds, as in the case of Microsoft. Other times, industry leaders form a consortium, such as the Java Community Process Program, to collectively develop a standard.The Wireless Application Protocol (WAP) forum

52、 became the initial industry groupthat set out to create standards for wireless technology. Ericsson, Motorola, Nokia, andUnwired Planet formed theWAP forum in 1997, and it has since grown to include nearlyall mobile device manufacturers, mobile network providers, and developers. The WAPforum create

53、d mobile communications device standards referred to as theWAP standard.The WAP standard is an enhancement of HTML, XML, and TCP/IP. One element of this standard is the Wireless Markup Language specification, which consists of a blend of HTML and XML and is used by developers to create documents tha

54、t can be displayed by a microbrowser. A microbrowser is a diminutive web browser that operates on a mobile communications device.The WAP standard also includes specifications for aWireless Telephony ApplicationInterface (WTAI) specification and the WMLScript specification. WTAI is used to create an

55、interface for applications that run on a mobile communications device. WMLScript is a stripped-down version of JavaScript.9 J2ME applications J2ME applications referred to as a MIDlet can run on practically any mobilecommunications device that implements a JVM and MIDP. This encourages developersto

56、invest time and money in building applications for mobile communications deviceswithout the risk that the application is device dependent. However, J2ME isnt seen asa replacement for the WAP specification because both are complementary technologies.Developers whose applications are light-client base

57、d continue to use WML andWMLScript. Developers turn to J2ME for heavier clients that require sophisticatedprocessing on the mobile communications device.J2ME和Java领域1 介绍20世纪70年代以来随着计算机革命的开始，对计算机先进软件的需求大大增加，从而可以充分利用功能日益增强的精密的计算机的处理数据的能力。C编程语言逐渐成为支柱，使程序员开发软件像计算机运行一样流畅。80年代以来，程序员又目睹了编程语言领域的又一次变革的高潮。C语言的

58、编程能力已经不能满足计算机的技术发展的需要。这问题并不是新问题。它造成了一代又一代的编程语言的新老更替。问题是，它使得程序设计过于复杂，从而使计算机软件的设计，编写和开发落后于硬件的发展。就是这个时候，两种基于设计概念的编程语言Simula 67和Smalltalk （从上世纪60年代末）带来了接近编程语言未来前景的循序渐进的步骤。这期间，当面向对象编程（ OOP ）， 与它一种新的编程语言，所谓的C + +在程序员中掀起了一场风暴。1979年， Bjarne Stroustrup的在新泽西州的贝尔实验室增强了C 语言，使其具有面向对象的特点即所谓的C + + 语言 （ + +是C编程语言增强

59、的承载符号 ）。 C + +是一个真正的提高的C编程语言，它开始是一种前置语言，该计划最初是一种编译工具。 Stroustrup建立类的概念（借用了Simula 67和Smalltalk 中的概念） ，由类则可以创建实例对象。一个类包含数据成员和定义对象数据和功能的成员函数。他还介绍了继承的概念，使一类继承其他一个或多个类的部分或全部数据成员或成员函数，职能由一个或多个其他类别-所有这些概念就是面向对象的编程。1988年由ANSI官员将C + +标准化。走进JAVA正当C + +作为企业开发所选择的语言时，由于最新的突破性技术-万维网的出现，别一种编程语言正在萌芽，并逐渐成熟。几十年来互联网对

60、普通人来说还是个秘密，直到前美国国家科学基金会（监督互联网的机构）拆除了防止互联网商业化的壁垒。1991年当它向商贸开放时，互联网几乎是政府机构和学术团体的专利。一旦商业化的障碍被取消，万维网提供的几个服务，在互联网上成为虚拟社区中心，游客可以得到几乎任何的免费的资讯并浏览数以千计的虚拟商店。 浏览器加强了万维网。浏览器转换将用HTML编写的ASCII文本文件转化成为一个互动的显示功能，并可以任何计算机上编译运行。只要浏览器是和HTML和HTTP兼容的正确版本， 在任何电脑上运行的浏览器可以使用相同的HTML文件，而不是指定为某一特定类型的计算机，而在以前是闻所未闻的。而C或C + +是依赖于

61、机器的，并且不能运行于不同机器上，除非是重新编译。互联网的成功使人们将重点放在发展独立于机器的编程语言上。和同年在互联网上被商品化，科技工作者SunMicrosystems詹姆斯戈斯林，帕特里克诺顿， chriswarth ，和麦克谢里登花了18个月发展规划，并在1995年向公众发布，他们所谓的Oak，后来改名为Java。Java 在1991年和1995年期间经历了无数次的变革。那个时候，在Sun公司的许多其他科技人员对该语言的发展做出了重大贡献。Joy，阿瑟范霍夫，乔纳森佩恩， Yelin ， 添佩尔都分享了成功的喜悦。 虽然Java是和互联网密切相关，但开始是为了开发一种可以嵌入到电子器件

62、中去的软件的编程语言，而无论所用装置的CPU类型。这也是众所周知的所谓embedded java平台。Java团队从Sun成功地建立了一种可移植性的编程语言，电脑程序员进行了首次编程，一些已经实现。他们的成功远远超出了他们的梦想。同样可以使Java程序进行在各种可移植的电子装置上，也可以使Java程序在安装了Microsoft Windows ， UNIX和Macintosh的计算机上运行。 这个时机很完美。因特网/内部网已使美国企业为符合公司成本效益，而开发应用于公司的可移植程序的兴趣。Java已被证明可以作为一种成功开发与机器无关的应用程序的编程语言。 Java虚拟机写Java程序和写C

63、+ +程序是相似的，这程序员可以编写： 包含指示的源代码，成为一个编辑器，或在一个综合发展环境中对源代码进行编译。不过，这也就是Java和C + + 一部分的方式。该编译和链接的过程中一个C + +程序的结果可以运行在一个适当的可执行的机器上。与此相反，Java编译器则将Java 源代码转换成字节，即由Java虚拟机（ JVM ）执行 。机器的具体指示，则不会包括在字节中。相反，他们已经包括在JVM的，这是属于具体机器的。这意味着该字节可能包含的C + +程序要翻译的指令要少。未来的世界：J2ME请记住， Java是在消费和工业产品中作为一种编程语言创建程序嵌入式系统微机发现的开始，如那些用来

64、控制汽车和家用电器的微机。在20世纪90年代初，开发团队在Sun的工作利用Java以解决幼稚的嵌入式电脑市场的编程的需要，但这种努力是更侧重于来自互联网的吸引力的机会。在世纪交替之年由于这些机会已得到解决，一种新的便携式通信带来了其他设备的机会。从语音通信设备的语音到文本通信设备。而便携式电子电话簿演变成个人数码助理。在这时候，芯片制造商所推出的新产品，其目的是为了从桌上型电脑转移计算能力到移动的小型电脑控制的燃气水泵，电缆电视盒，和其他组合的其他电器。为下一步的演变的Java的时机是合理的 。不过，不是Java 与额外的空气污染指数加强，在Sun公司的该小组，即Java Community

65、Process计划， 拆除均采用Java编程语言和Java虚拟机。他们从嵌入式系统和微机设备剥离下来的Java的API和JVM到最低限度编码须提供情报。由于这些设备资源方面的限制强加的硬件设计，这是必要的。他们的努力结果是J2ME的。 J2ME是减少了Java API和Java虚拟机是设计用来运作稀疏可用的资源在新的品种的嵌入式计算机和微机的版本。组织J2ME传统计算设备需要使用标准相当的硬件配置，如显示器，键盘，鼠标和大量的记忆和永久储存。不过，其中新一代的计算设备缺乏的硬件配置的连续性。有些设备不具有显示屏，永久储存，键盘， 或鼠标。其中小的计算设备的记忆提供情况是不一致的。缺乏统一标准的硬件配置之间的小型计算设备的构成是一项艰巨的挑战Java Community Process的计划则是为JVM和J2ME的小型计算设备制定标准。 许多不同种的小的J2ME的计算设备，包括screen phones ，数字机顶盒用于有线电视，手机和个人数字助理，所面临的挑战是Java Community Process的计划是建立一个可以对小的无标准的计算设备实施的Java标准。J2ME Profile一个配置文件构成的Java类，其执行