【正文】 經(jīng)濟(jì)上的主要?jiǎng)訖C(jī)便是能夠以class libraries 的形式，輕松地重復(fù)運(yùn)用既有的程序代碼（本書廣泛使用的Java 標(biāo)準(zhǔn)鏈接庫更是如此）。4．使用既有的鏈接庫（libraries）更換跑道至OOP這一點(diǎn)，也可能沒有發(fā)現(xiàn)到鏈接庫的存在，抑或過度迷戀程序語言的魅力，總想自己動(dòng)手寫一些早已存在的classes。就算沒有人恰巧解決你的問題，你也有可能應(yīng)用所學(xué)，修改他人設(shè)計(jì)的抽象方法，套用在自己的需求上。3．向成功借鏡起跑之前，先找一些有著良好對象導(dǎo)向設(shè)計(jì)的范例出來閱讀。第一個(gè)項(xiàng)目可能無法一蹴而成，所以不應(yīng)該挑選會(huì)對公司產(chǎn)生重大影響的案子。2．低風(fēng)險(xiǎn)專案先以低風(fēng)險(xiǎn)項(xiàng)目做為試探，并允許錯(cuò)誤發(fā)生。這種方式特別適合小型公司進(jìn)行根本性的移轉(zhuǎn)，或是對大型公司的部門層次來進(jìn)行。挑選一小群人來進(jìn)行教育，這一小群人最好是個(gè)性好奇、能夠彼此合作、能夠在學(xué)習(xí)Java 的時(shí)候彼此奧援的人。實(shí)踐準(zhǔn)則想要過渡到OOP 和Java，可以參考以下建議的實(shí)踐準(zhǔn)則：1．訓(xùn)練第一步便是某種形式的教育。這就是有經(jīng)驗(yàn)的程序員轉(zhuǎn)換到Java 跑道時(shí)可以采取的方式。接下來就是一個(gè)「真實(shí)世界」中的項(xiàng)目，這個(gè)項(xiàng)目真的能夠做一些有用的事情。過渡策略如果你大量采用OOP，那么你的下一個(gè)問題可能是：「我要如何才能夠讓我的上司、同事、部門、同儕們都開始使用對象呢？」想想你，一個(gè)獨(dú)立的程序員，如何開始學(xué)習(xí)一個(gè)全新的程序語言和一個(gè)全新的設(shè)計(jì)思維？其實(shí)你辦到了。如果你只是想寫一個(gè) Hello World 小程序，當(dāng)然不需動(dòng)用OOP，但是當(dāng)你需要用到時(shí)，這些功能唾手可得。就這樣不知不覺付出了額外的成本。即使存在界線，你還是會(huì)忽略它。但是當(dāng)程序的長度超過數(shù)頁，或是逾越該語言的標(biāo)準(zhǔn)題域之外，你就會(huì)像「在一池黏稠液體中游泳」一樣，動(dòng)彈不得。大型程序設(shè)計(jì)對于程序的大小和復(fù)雜度，許多傳統(tǒng)語言都存在若干內(nèi)建限制。如果你所開發(fā)的程序很大，很復(fù)雜，那么大概沒有什么事比得上「程序某處暗藏一個(gè)錯(cuò)誤，我們卻對其發(fā)生原因毫無頭緒」還要糟糕吧。由于Java 編譯器會(huì)留意鏈接庫被使用的方式——保證初始化動(dòng)作和清除動(dòng)作確實(shí)正確地執(zhí)行，并確保呼叫函式的方式合乎規(guī)矩——你可以專注于鏈接庫的運(yùn)用，而不必?fù)?dān)心如何制造它們。將鏈接庫轉(zhuǎn)換為新的data types（classes）便是Java 達(dá)成此一目標(biāo)的手段。透過鏈接庫（libraries）發(fā)揮最大杠桿效應(yīng)開發(fā)程序的最快途徑，就是使用現(xiàn)成的東西：鏈接庫（library）。如果程序易于理解，便相對地易于維護(hù)。如此一來便能夠以高階觀念來處理問題，而且每一行程序代碼可以做的事情就更多了。易于表達(dá)、易于理解的系統(tǒng)Systems are easier to express and understand被設(shè)計(jì)用來「與待解問題相稱」的class，先天上就有較佳的表述能力。生產(chǎn)力來自于許多層面，但是Java 語言希望從語言層面提供盡可能的協(xié)助。 in any case it’s not an issue while you’re in rapiddevelopment mode. When you have a system that you like, if it’s small and fast enough, then you’re done. If not, you begin tuning with a profiling tool, looking first for speedups that can be done by rewriting small portions of code. If that doesn’t help, you look for modifications that can be made in the underlying implementation so no code that uses a particular class needs to be changed. Only if nothing else solves the problem do you need to change the design. The fact that performance is so critical in that portion of the design is an indicator that it must be part of the primary design criteria. You have the benefit of finding this out early using rapid development.If you find a function that is a particular bottleneck, you can rewrite it in C/C++ using Java’s native methods. 附錄B 中文譯文Java為什么成功Java 能夠取得如此的成功，原因在于其目標(biāo)的設(shè)定：為當(dāng)今開發(fā)人員解決他們所面臨的諸多問題。 then es a trial project to give you a feel for the basics without doing anything too confusing. Then es a “real world” project that actually does something useful. Throughout your first projects you continue your education by reading, asking questions of experts, and trading hints with friends. This is the approach many experienced programmers suggest for the switch to Java. Switching an entire pany will of course introduce certain group dynamics, but it will help at each step to remember how one person would do it. GuidelinesHere are some guidelines to consider when making the transition to OOP and Java: 1. TrainingThe first step is some form of education. Remember the pany’s investment in code, and try not to throw everything into disarray for six to nine months while everyone puzzles over how interfaces work. Pick a small group for indoctrination, preferably one posed of people who are curious, work well together, and can function as their own support network while they’re learning Java.An alternative approach that is sometimes suggested is the education of all pany levels at once, including overview courses for strategic managers as well as design and programming courses for project builders. This is especially good for smaller panies making fundamental shifts in the way they do things, or at the division level of larger panies. Because the cost is higher, however, some may choose to start with projectlevel training, do a pilot project (possibly with an outside mentor), and let the project team bee the teachers for the rest of the pany. 2. Lowrisk projectTry a lowrisk project first and allow for mistakes. Once you’ve gained some experience, you can either seed other projects from members of this first team or use the team members as an OOP technical support staff. This first project may not work right the first time, so it should not be missioncritical for the pany. It should be simple, selfcontained, and instructive。 Java language design decisions were based on providing the maximum benefits to the programmer. Systems are easier to express and understandClasses designed to fit the problem tend to express it better. This means that when you write the code, you’re describing your solution in the terms of the problem space (“Put the grommet in the bin”) rather than the terms of the puter, which is the solution space (“Set the bit in the chip that means that the relay will close”). You deal with higherlevel concepts and can do much more with a single line of code. The other benefit of this ease of expression is maintenance, which (if reports can be believed) takes a huge portion of the cost over a program’s lifetime. If a program is easier to understand, then it’s easier to maintain. This can also reduce the cost of creating and maintaining the documentation. Maximal leverage with librariesThe fastest way to create a program is to use code that’s already written: a library. A major goal in Java is to make library use easier. This is acplished by casting libraries into new data types (classes), so that bringing in a library means adding new types to the language. Because the Java piler takes care of how the library is used—guaranteeing proper initialization and cleanup, and ensuring that functions are called properly—you can focus on what you want the library to do, not how you have to do it. Error handlingError handling in C is a notorious problem, and one that is often ignored—fingercrossing is usually involved. If you’re building a large, plex program, there’s nothing worse than having an error buried somewhere with no clue as to where it came from. Java exception handling is a way to guarantee that an error is noticed, and that something happens as a result. Programming in the largeMany