【導(dǎo)讀】對于一個名副其實的程序設(shè)計人員來說，使。用Java無疑是一個好的選擇。Java是一個完整的平臺，有一個龐大的庫，其中包含很多可重用的代碼和。Java這種功能齊全的出色語言，具有高質(zhì)量的執(zhí)行環(huán)境以及龐大的。因此，盡管人們發(fā)現(xiàn)C++不太適用，但在設(shè)計Java的時候還是盡?？赡艿亟咏麮++，以便系統(tǒng)更易于理解。Java別除了C++中許多很少使用、難以理。的確，Java語法是C++語法的一個“純凈”版本。給出的C++注釋，那里比較詳細(xì)地解釋了Java與C++之間的區(qū)別。并沒有試圖清除C++中所有不適當(dāng)?shù)奶匦?。Java的目標(biāo)之一是支持開發(fā)能夠在小型機(jī)器上獨立。在本質(zhì)上，Java的面向?qū)ο竽芰εcC++是一樣的。Java與C++的主要不同點在于多繼承，在Java中，取而代之的是簡單的接口。而引起內(nèi)存沖突的人來說，一定很喜歡Java的這一特性。在任何情況下，蒙騙Java的安全機(jī)制都是十分困難的。·未經(jīng)授權(quán)禁止讀寫文件。許多安全特性相繼不斷地被加入Java中

　　

【正文】 pilation, the justintime (JIT) pilers. These work by piling the bytecodes into native code once, caching the results, and then calling them again if needed. This approach speeds up monly used code tremendously because one has to do the interpretation only once. Although still slightly slower than a true native code piler, a justintime piler can give you a 10 or even 20fold speedup for some programs and will almost always be significantly faster than an interpreter. This technology is being improved continuously and may eventually yield results that cannot be matched by traditional pilation systems. For example, a justintime piler can monitor which code is executed frequently and optimize just that code for speed. 10. Multithreaded The enefits of multithreading are better interactive responsiveness and realtime you have ever tried to do multithreading in another language, you will be pleasantly surprised at how easy it is in Java. Threads in Java also can take advantage of multiprocessor systems if the base operating system does so. On the downside, thread implementations on the major platforms differ widely, and Java makes no effort to be platform independent in this regard. Only the code for calling multithreading remains the same across machines。 Java offloads the implementation of multithreading to the underlying operating system or a thread library. Noheless, the ease of multithreading is one of the main reasons why Java is such an appealing language for serverside development. 11. Dynamic In a number of ways, Java is a more dynamic language than C or C++. It was designed to adapt to an evolving environment. Libraries can freely add new methods and instance variables without any effect on their clients. In Java, finding out run time type information is straightforward. This is an important feature in those situations in which code needs to be added to a running program. A prime example is code that is downloaded from the Inter to run in a browser. In Java , finding out runtime type information was anything but straightforward, but current versions of Java give the programmer full insight into both the structure and behavior of its objects. This is extremely useful for systems that need to analyze objects at run time, such as Java GUI builders, smart debuggers, pluggable ponents, and object databases. Java and the Inter The idea here is simple: users will download Java bytecodes from the Inter and run them on their own machines. Java programs that work on web pages are called applets. To use an applet, you need a Javaenabled web browser, which will execute the bytecodes for you. Because Sun is licensing the Java source code and insisting that there be no changes in the language and basic library structure, a Java applet should run on any browser that is advertised as Javaenabled. Unfortunately, reality has been different. Various versions of Netscape and Inter Explorer run different versions of Java, some of which are seriously outdated. This sorry situation made it increasingly difficult to develop applets that take advantage of the most current Java version. To remedy this problem, Sun has developed the Java Plugin, a tool that makes the newest Java runtime environment available to both Netscape and Inter Explorer When the user downloads an applet, it works much like embedding an image in a web page. The applet bees a part of the page, and the text flows around the space used for the applet. The point is, the image is alive. It reacts to user mands, changes its appearance, and sends data between the puter presenting the applet and the puter serving it. a good example of a dynamic web page— an applet to view molecules— that carries out sophisticated calculations. By using the mouse, you can rotate and zoom each molecule to better understand its structure. This kind of direct manipulation is not achievable with static web pages, but applets make it possible. Common Misconceptions About Java This is a list of some mon misconceptions about Java, along with mentary. Java is an extension of HTML. Java is a programming language。 HTML is a way to describe the structure of a web page. They have nothing in mon except that there are HTML extensions for placing Java applets on a web page. I use XML, so I don39。t need Java. Java is a programming language。 XML is a way to describe data. You can process XML data with any programming language, but the Java API contains excellent support for XML processing. In addition, many important thirdparty XML tools are implemented in Java. See Volume 2 for more information. Java is an easy programming language to learn. No programming language as powerful as Java is easy. You always have to distinguish between how easy it is to write toy programs and how hard it is to do serious work. Also, consider that only four chapters in this book discuss the Java language. The remaining chapters of both volumes show how to put the language to work, using the Java libraries. The Java libraries contain thousands of classes and interfaces, and tens of thousands of functions. Luckily, you do not need to know every one of them, but you do need to know surprisingly many to use Java for anything realistic. Java will bee a universal programming language for all platforms. This is possible, in theory, and it is certainly the case that every vendor but Microsoft seems to want this to happen. However, many applications, already working perfectly well on desktops, would not work well on other devices or inside a browser. Also, these applications have been written to take advantage of the speed of the processor and the native user interface library and have been ported to all the important platforms anyway. Among these kinds of applications are word processors, photo editors, and web browse