2022年Java毕设论文英文翻译.pdf

Java 毕设论文英文翻译Java and the Internet If Java is, in fact, yet another computer programming language, you may question why it is so important and why it is being promoted as a revolutionary step in computer programming、 The answer isn t immediately obvious if youre coming from a traditional programming perspective、 Although Java is very useful for solving traditional standalone programming problems, it is also important because it will solve programming problems on the World Wide Web、What is the Web? The Web can seem a bit of a mystery at first, with all this talk of “surfing,”“presence,” and “home pages、” It s helpful to step back and see what it really is, but to do this you must understand client/server systems, another aspect of computing that s full of confusing issues 、Client/Servercomputing The primary idea of a client/server system is that you have a central repository of information some kind of data, often in a databasethat you want to distribute on demand to some set of people or machines、 A key to the client/server concept is that the repository of information is centrally located so that it an be changed and so that those changes will propagate out to the information consumers 、 Taken together, the information repository, the software that distributes the information, and the machine(s) where the information and software reside is called the server 、 The software that resides on the remote machine, communicates with the server, fetches the information, processes it, and then displays it on the remote machine is called the client、The basic concept of client/server computing, then, is not so complicated、 The problems arise because you have a single server trying to serve many clients at once、 Generally, a database management system is involved, so the designer “balances ” the layout of data into tables for optimal use、 In addition, systems often allow a client to insert new information into a server、 This means you must ensure that one cl ient s new data doesn t walk over another clientsnew data, or that data isn t lost in the process of adding it to the database (this is called transaction processing) 、 As client software changes, it must be built, debugged, and installed on the client machines, which turns out to be more complicated and expensive than you might think、 It s especially problematic to support multiple types of computers and operating systems、 Finally, there s the all-important performance issue: You might have hundreds of clients making requests of your server at any one time, so any small delay is crucial、 To minimize latency, programmers work hard to offload processing tasks, often to the client machine, but sometimes to other machines at the server site, using so-called middleware、 (Middleware is also used to improve maintainability、 ) 精品资料 - - - 欢迎下载 - - - - - - - - - - - 欢迎下载 名师归纳 - - - - - - - - - -第 1 页，共 9 页 - - - - - - - - - - Java 毕设论文英文翻译The simple idea of distributing information has so many layers of complexity that the whole problem can seem hopelessly enigmatic、 And yet it s crucial: Client/server computing accounts for roughly half of all programming activities、 It s responsible for everything from taking orders and credit-car d transactions to the distribution of any kind of datastock market, scientific, government, you name it 、 What weve come up with in the past is individual solutions to individual problems, inventing a new solution each time、 These were hard to create and hard to use, and the user had to learn a new interface for each one、The entire client/server problem needs to be solved in a big way、The Web asagiant serverThe Web is actually one giant client/server system、 It s a bit worse than that, since you have all the servers and clients coexisting on a single network at once、 You dont need to know that, because all you care about is connecting to and interacting with one server at a time (even though you might be hopping around the world in your search for the correct server)、 Initially it was a simple one-way process 、 You made a request of a server and it handed you a file, which your machine s browser software (i 、e、, the client) would interpret by formatting onto your local machine、 But in short order people began wanting to do more than just deliver pages from a server、 They wanted full client/server capability so that the client could feed information back to the server, for example, to do database look ups on the server, to add new information to the server, or to place an order (which required more security than the original systems offered)、 These are the changes weve been seeing in the development of the Web、The Web browser was a big step forward: the concept that one piece of information could be displayed on any type of computer without change、 However, browsers were still rather primitive and rapidly bogged down by the demands placed on them、 They weren t particularly interactive, and tended to clog up both the server and the Internet because any time you needed to do something that required programming you had to send information back to the server to be processed、 It could take many seconds or minutes to find out you had misspelled something in your request、 Since the browser was just a viewer it couldnt perform even the simplest computing tasks、 (On the other hand, it was safe, because it couldn t execute any programs on your local machine that might contain bugs or viruses、) To solve this problem, different approaches have been taken 、 To begin with, graphics standards have been enhanced to allow better animation and video within browsers 、 The remainder of the problem can be solved only by incorporating the ability to run programs on the client end, under the browser、 This is called client-side programming、Client-side programming 精品资料 - - - 欢迎下载 - - - - - - - - - - - 欢迎下载 名师归纳 - - - - - - - - - -第 2 页，共 9 页 - - - - - - - - - - Java 毕设论文英文翻译The Web s initial server-browser design provided for interactive content, but the interactivity was completely provided by the server、 The server produced static pages for the client browser, which would simply interpret and display them、 Basic HyperText Markup Language (HTML) contains simple mechanisms for data gathering: text-entry boxes, check boxes, radio boxes, lists and drop-down lists, as well as a button that can only be programmed to reset the data on the form or “submit ” the data on the form back to the server、 This submission passes through the Common Gateway Interface (CGI) provided on all Web servers、 The text within the submission tells CGI what to do with it、 The most common action is to run a program located on the server in a directory that s typically called “cgi -bin 、” (If you watch the address window at the top of your browser when you push a button on a Web page, you can sometimes see “cgi -bin ” within all the gobbledygook there、) These programs can be written in most languages 、 Perl has been a common choice because it is designed for text manipulation and is interpreted, so it can be installed on any server regardless of processor or operating system、 However, Python (my favoritesee ) has been making inroads because of its greater power and simplicity、Many powerful Web sites today are built strictly on CGI, and you can in fact do nearly anything with CGI、 However, Web sites built on CGI programs can rapidly become overly complicated to maintain, and there is also the problem of response time 、 The response of a CGI program depends on how much data must be sent, as well as the load on both the server and the Internet、 (On top of this, starting a CGI program tends to be slow、) The initial designers of the Web did not foresee how rapidly this bandwidth would be exhausted for the kinds of applications people developed、 For example, any sort of dynamic graphing is nearly impossible to perform with consistency because a Graphics Interchange Format (GIF) be created and moved from the server to the client for each version of the graph 、 And youve no doubt had direct experience with something as simple as validating the data on an input form、 You press the submit button on a page; the data is shipped back to the server; the server starts a CGI program that discovers an error, formats an HTML page informing you of the error, and then sends the page back to you; you must then back up a page and try again 、 Not only is this slow, it s inelegant、 The solution is client-side programming、 Most machines that run Web browsers are powerful engines capable of doing vast work, and with the original static HTML approach they are sitting there, just idly waiting for the server to dish up the next page 、 Client-side programming means that the Web browser is harnessed to do whatever work it can, and the result for the user is a much speedier and more interactive experience at your Web site、 The problem with discussions of client-side programming is that they aren t very different from discussions of programming in general、 The parameters are almost the same, but the platform is different; a Web browser is like a limited operating system、In the end, you must still program, and this accounts for the dizzying array of p精品资料 - - - 欢迎下载 - - - - - - - - - - - 欢迎下载 名师归纳 - - - - - - - - - -第 3 页，共 9 页 - - - - - - - - - - Java 毕设论文英文翻译roblems and solutions produced by client-side programming、 The rest of this section provides an overview of the issues and approaches in client-side programming 、Plug-insOne of the most significant steps forward in client-side programming is the development of the plug-in、 This is a way for a programmer to add new functionality to the browser by downloading a piece of code that plugs itself into the appropriate spot in the browser、 It tells the browser “from now on you can perform this new activity 、” (You need to download the plug-in only once、) Some fast and powerful behavior is added to browsers via plug-ins, but writing a plug-in is not a trivial task, and isn t something youd want to do as part of the process of building a particular site、 The value of the plug-in for client-side programming is that it allows an expert programmer to develop a new language and add that language to a browser without the permission of the browser manufacturer 、 Thus, plug-ins provide a “back door ” that allows the creation of new client-side programming languages (although not all languages are implemented as plug-ins) 、ScriptinglanguagesPlug-ins resulted in an explosion of scripting languages、 With a scripting language, you embed the source code for your client-side program directly into the HTML page, and the plug-in that interprets that language is automatically activated while the HTML page is being displayed、 Scripting languages tend to be reasonably easy to understand and, because they are simply text that is part of an HTML page, they load very quickly as part of the single server hit required to procure that page、 The trade-off is that your code is exposed for everyone to see (and steal) 、 Generally, however, you aren t doing amazingly sophisticated things with scripting languages, so this is not too much of a hardship、This points out that the scripting languages used inside Web browsers are really intended to solve specific types of problems, primarily the creation of richer and more interactive graphical user interfaces (GUIs)、 However, a scripting language might solve 80 percent of the problems encountered in client-side programming 、 Your problems might very well fit completely within that 80 percent,and since scripting languages can allow easier and faster development, you should probably consider a scripting language before looking at a more involved solution such as Java or ActiveX programming、精品资料 - - - 欢迎下载 - - - - - - - - - - - 欢迎下载 名师归纳 - - - - - - - - - -第 4 页，共 9 页 - - - - - - - - - - Java 毕设论文英文翻译The most commonly discussed browser scripting languages are JavaScript (which has nothing to do with Java; it s named that way just to grab some of Javas marketing momentum), VBScript (which looks like Visual BASIC), and Tcl/Tk, which comes from the popular cross-platform GUI-building language、 There are others out there, and no doubt more in development、JavaScript is probably the most commonly supported、 It comes built into both Netscape Navigator and the Microsoft Internet Explorer (IE)、 Unfortunately, the flavor of JavaScript on the two browsers can vary widely (the Mozilla browser, freely downloadable from , supports the ECMAScript standard, which may one day become universally supported)、 In addition, there are probably more JavaScript books available than there are for the other browser languages, and some tools automatically create pages using JavaScript、 However, if youre already fluent in Visual BASIC or Tcl/Tk, youll be more productive using those scripting languages rather than learning a new one、 (You ll have your hands full dealing with the Web issues already、) ja va与因特网既然 Jav a不过另一种类型的程序设计语言, 大家可能会奇怪它为什么值得如此重视 , 为什么 还 有 这 么 多 的 人 认 为 它 就 是 计 算 机 程 序 设 计 的一 个 里 程 碑 呢 ？ 如 果 您 来 自 一 个 传 统 的 程 序 设计背景 , 那么答案在刚开始的时候并不就是很明显。jav a除了可解决传统的程序设计问题以外, 还能解决 World Wide Web( 万维网 ) 上的编程问题。1、 11、 1 什么就是web？web这个词刚开始显得有些泛泛, 似乎“ 冲浪 ” 、“ 网上存在 ” 以及 “ 主页 ” 等等都与它拉上了一些关系。甚至还有一种“Internet综合症 ” 的说法 , 对许多人狂热的上网行为提出了质疑。我们在这里有必要作一些深入的探讨, 但在这之前 , 必须理解客户机服务器系统的概念, 这就是充斥着许多令人迷惑的问题的又一个计算领域。1、 客户机服务器计算客户机服务器系统的基本思想就是我们能在一个统一的地方集中存放信息资源。 一般将数据集中保存在某个数据库中, 根据其她人或者机器的请求将信息投递给对方。客户机服务器概述的一个关键在于信息就是“ 集中存放 ”的。所以我们能方便地更改信息, 然后将修改过的信息发放给信息的消费者。将各种元素集中到一起, 信息仓库、用于投递信息的软件以及信息及软件所在的那台机器 , 它们联合起来便叫作“ 服务器 ” (server)。而对那些驻留在程机器上的软件 , 它们需要与服务器通信, 取回信息 , 进 行 适 当 的 处 理 , 然后在远程机器上显示出来, 这些就叫作 “ 客户 ” (client)。 这样瞧来 , 客户机服务器的基本概念并不复杂。这里要注意的一个主要问题就是单个服务器精品资料 - - - 欢迎下载 - - - - - - - - - - - 欢迎下载 名师归纳 - - - - - - - - - -第 5 页，共 9 页 - - - - - - - - - - Java 毕设论文英文翻译需要同时向多个客户提供服务。在这一机制中, 通常少不了一套数据库管理系统, 使设计人员能将数据布局封装到表格中, 以获得最优的使用。除此以外,系统经常允许客户将新信息插入一个服务器。这意味着必须确保客户的新数据不会与其她客户的新数据冲突, 或者说需要保证那些数据在加入数据库的时候不会丢失 (用数据库的术语来说, 这叫作 “ 事务处理 ” ) 。 客户软件发生了改变之后 , 它们必须在客户机器上构建、调试以及安装。所有这些会使问题变得比我们一般想象的复杂得多。另外, 对多种类型的计算机与操作系统的支持也就是一个大问题。最后 , 性能的问题显得尤为重要: 可能会有数百个客户同时向服务器发出请求。所以任何微小的延误都就是不能忽视的。为尽可能缓解潜伏的问题, 程序员需要谨慎地分散任务的处理负担。一般可以考虑让客户机负担部分处理任务, 但有时亦可分派给服务器所在地的其她机器, 那些机器亦叫作 “ 中间件 ” ( 中间件也用于改进对系统的维护) 。所以在具体实现的时候, 其她人发布信息这样一个简单的概念可能变得异常复杂。有时甚至会使人产生完全无从着手的感觉。客户机服务器的概念在这时就可以大显身手了。事实上 , 大约有一半的程序设计活动都可以采用客户机服务器的结构。这种系统可负责从处理订单及信用卡交易, 一直到发布各类数据的方方面面的任务 股票市场、科学研究、政府运作等等。在过去 , 我们一般为单独的问题采取单独的解决方案 ; 每 次都 要 设 计 一 套 新 方 案 。 这些方案无论创建还就是使用都比较困难 , 用户每次都要学习与适应新界面。客户机服务器问题需要从根本上加以变革！2 、 we b就是一个巨大的服务器web实 际 就 就 是 一 套 规 模巨 大 的 客 户 机 服 务 器 系 统 。但 它 的情 况 要复 杂 一 些 , 因 为 所 有 服 务器与客户都同时存在于单个网络上面。但我们没必要了解更进一步的细节, 因为唯一要关心的就就是一次建立同一个服务器的连接 , 并同它打交道 ( 即使可能要在全世界的范围内搜索正确的服务器)。最开始的时候 , 这就是一个简单的单向操作过程。我们向一个服务器发出请求它向我们回传一个文件, 由于本机的浏览器软件( 亦即 “ 客户 ” 或“ 客户程序 ” ) 负责解释与格式化, 并在我们面前的屏幕上正确地显示出来。但人们不久就不满足于只从一个服务器传递网页。她们希望获得完全的客户机服务器能力,使客户 ( 程序 ) 也 能 反 馈 一 些 信 息 到 服 务器 。比如希望对服务器上的数据库进行检索 , 向服务器添加新信息, 或者下一份订单等等( 这也提供了比以前的系统更高的安全要求)。 在 web的发展过程中 , 我们可以很清晰地瞧出这些令人心喜的变化。 web 浏 览器 的 发 展终 于 迈 出