Java语言与面向对象思想翻译(中英文)

Java语言与面向对象思想翻译（中英文）Java语言与面向对象思想Java，是由Sun Microsystems公司于1995年5月推出的Java程序设计语言和Java的总称。

用Java实现的Hot Java 浏览器(支持Java applet)显示了Java的魅力:跨平台、动态的Web、Internet计算。

从此，Java被广泛接受并推动了Web的迅速发展，常用的浏览器现在均支持Java applet。

1 Java语言的特点Java语言适用于Internet环境，是一种被广泛使用的网络编程语言，它具有如下的一些特点: 简单Java语言的语法规则和C++类似，但Java语言取消了指针和多重继承，统一使用引用来指示对象(C++中有两种形式，实际上是两种产生对象的途径，而Java 中只有一种)，通过自动垃圾收集免去了程序设计人员对于内存块的释放工作。

面向对象(近于完全)Java语言为了提高效率，定义了几个基本的数据类型以非类的方式实现，余下的所有数据类型都以类的形式进行封装，程序系统的构成单位也是类。

因而几乎可以认为是完全面向对象。

平台无关性(可移植、跨平台)Java虚拟机(JVM)是在各种体系结构真实机器中用软件模拟实现的一种想象机器，必要时候可以用硬件实现。

当然，这些虚拟机内部实现各异，但其功能是一致的——执行统一的Java虚拟机指令。

Java编译器将Java 应用程序的源代码文件(.java)翻译成Java字节码文件(.class),它是由Java虚拟机指令构成的。

由于是虚拟机器，因而Java虚拟机执行Java程序的过程一般称为解释。

依赖于虚拟机技术，Java语言具有与机器体系结构无关的特性，即Java程序一旦编写好之后，不需进行修改就可以移植到任何一台体系结构不同的机器上。

从操作系统的角度看，执行一次Java程序的过程就是执行一次Java 虚拟机进程的过程。

面向网络编程Java语言产生之初就面向网络，在JDK中包括了支持TCP/IP、HTTP和FTP等协议的类库。

多线程支持多线程是程序同时执行多个任务的一种功能。

多线程机制能够使应用程序并行执行多项任务，其同步机制保证了各线程对共享数据的正确操作。

良好的代码安全性运行时(Runtime)一词强调以动态的角度看程序，研究程序运行时候的动态变化，也用运行时环境一词表达类似的含义。

Java技术的很多工作是在运行时完成的，如加强代码安全性的校验操作。

一般地，Java技术的运行环境执行如下三大任务:加载代码——由类加载器执行类加载器为程序的执行加载所需要的全部类(尽可能而未必同时)。

校验代码——由字节码校验器执行Java代码在实际运行之前要经过几次测试。

字节码校验器对程序代码进行四遍校验，这可以保证代码符合JVM规范并且不破坏系统的完整性。

如,,检查伪造指针、违反对象访问权限或试图改变对象类型的非法代码。

执行代码——由运行时的解释器执行自动垃圾收集许多编程语言都允许在程序运行时动态分配内存块，分配内存块的过程由于语言句法不同而有所变化，但总是要返回指向存储区起始位置的指针。

在C，C++ 及其它一些语言中，程序员负责取消分配内存块。

有时这是一件很困难的事情。

因为程序员并不总是事先知道内存块应在何时被释放。

当在系统中没有能够被分配的内存块时，可导致程序瘫痪，这种程序被称作具有内存漏洞。

当分配内存块不再需要时，程序或运行环境应取消分配内存块。

垃圾收集就是将不再需要的已分配内存块回收。

在其它一般的语言中，取消分配是程序员的责任。

Java编程语言提供了一种系统级线程以跟踪存储区分配，来完成垃圾收集:可检查和释放不再需要的存储块可自动完成上述工作可在JVM实现周期中，产生意想不到的变化良好的代码健壮性Java能够检查程序在编译和运行时的错误。

类型检查能帮助用户检查出许多在开发早期出现的错误。

同时很多集成开发工具(IDE)的出现使编译和运行Java程序更加容易，并且很多集成开发工具(如Eclipse)都是免费的。

2 面向对象与面向过程的差异一种程序设计语言的产生，不仅是程序设计技术的改进，也包含了表达和认知思想的进步。

以C语言为代表的部分早期语言，被称为面向过程的语言，不仅因为其程序设计的表达形式是以过程为基本元素，本质上更在于此时对计算机化的系统的理解的主导思想还是控制流或者数据流的，构成系统的要素是模块——处理逻辑。

面向对象语言的产生，是因为对于系统的理解或抽象到了更为高级的层次。

此时的认知思想不仅更接近于现实世界，其抽象程度也很高。

因而，既有易懂的一方面，也有难懂的另一方面，就看理解的境界了。

2.1 面向过程思想回顾面向过程思想和程序设计语言的体现，可以简单总结为以下几条:对系统的认识采用结构化分析的过程——自顶向下，逐步求精地进行功能分解; 每个功能就是处理数据的一个模块，因而IPO描述充分刻画了模块的内外特征; 每个模块都是控制流的，因而有典型的三种程序结构——顺序、分支、循环; 模块间的关系通过调用维系，因而模块成为了函数，这也是面向过程方式下最主要的代码重用方式;尽管函数调用有参数和返回值，但数据总是和函数分开的，不仅有了著名的断言——程序=算法+数据，也使得绝对平等产生了无序的麻烦——所有的函数和数据的关联关系没有限制;如果要使用数据流，那么只能是在数据产生之后的适当时机调用函数。

这一时期的主要缺点是:对系统的理解比较难，系统地开发效率低，代码的可重用性差。

2.2 面向对象思想介绍面向对象思想，对现实世界采用直观的理解，计算机化时候采用深度的抽象，简单地可以总结如下:系统是由事物构成的，事物之间是有联系的，复杂的事物也是系统;系统与系统、系统与事物、事物与事物之间是有明确界限(边界)的;系统或事物的状态刻画可以用属性表示，属性一般是些简单的数据，如果复杂那就是事物了;系统或事物的状态会发生变化，称为行为，产生变化是有原因的(内部的或外部的)，变化的过程可能是复杂的;不同的事物之间会具有共同的属性和行为，共同的极端情形就是完全包含。

基于以上的认识，一个运行时(动态)的具体系统或事物，是由几个更小的具体事物构成(极端的事物就是一个简单的属性数据)，它们是不断发生变化的。

如果对事物这一概念进行了有效的抽象，那么问题就迎刃而解。

首先，将任何一个具体的事物称为对象(Object),它的极端情形就是过去的变量;事物是分类的，每一类事物都具有统一的属性和行为，即类型——抽象数据类型，简称为类(Class);行为既然是过程，那么就抽象成函数，命名为方法，以示区别。

例如:描述身高或姓名，各自只是一个简单的数据变量;描述一个学生，可以使用学号、姓名、宿舍、班级等;那更换宿舍算什么呢～那描述宿舍、班级，又要有许多个项目。

3面向对象程序设计中的主要概念和特征面向对象程序设计(Object Oriented Programming，OOP)语言中，为了进行更为高度的抽象，会引入一些现实世界中难于找到的概念，但对于一个程序语言来说确实很有价值的。

以下暂时介绍的概念基本上都来源于对现实世界的抽象，要从程序设计的角色中去理解它们。

面向对象程序设计使系统更易于理解，也使代码具有更好的重用性、可扩展性、易于管理和维护。

3.1 主要概念(1)、类类是对一类事物的抽象表示，其角色就相当于数据类型，当然可以算作复杂的数据类型。

如学生、宿舍、班级。

(2)、对象对象表示一个具体的事物，其角色就是变量，即一个复杂数据类型——xx类的变量。

如周瑜、张飞、瑜飞居，飞虎班。

(3)、成员一个事物的构成元素，讨论类的时候就是虚拟的，讨论对象的时候就是具体的。

如在类中，一个变量属于成员——成员变量，一个对象也属于成员——成员对象，一个函数也属于成员——成员方法。

3.2 主要特征OOP语言有三个特征:封装、继承及多态性。

(1)、封装类的构成包括成员变量/对象与成员方法，这样将相关的数据与函数包装在一起，同其他的类相区分，就是封装。

显然，避免了面向过程语言的平行缺陷，说明了类和成员之间的所属关系。

进一步地，可以限制类的成员在外部的可见性，那么就将封装体现得更完美。

(2)、继承当一种事物甲完全是另一种事物乙的特例，那么，一般地，类甲只是比类乙多出一些成员变量/对象与成员方法，称为类甲继承类乙，类甲称为(类乙的)子类，类乙称为(类甲的)父类。

父类也称为基类、超类，子类也称为导出类、派生类。

显然编写子类就没有必要重复书写父类中乙有的代码部分，这是OOP中最典型的代码重用。

(3)、多态多态表示一个类的某种行为存在多种实现版本。

简单的情况是在一个类中，给出多种不同的实现，复杂的情况是在多个子类中各自给出不同的实现。

Overview of Java languageJava, from Sun Microsystems, launched in May 1995 of the Java programming language and Java in general. Hot Java implementation with Java browser (supporting Java applet) shows the charm of Java: cross-platform, dynamic Web, Internet computing. Since then, Java is widely accepted and promoted the rapid development of Web, popular browsers now support Java applet1 Java Language FeaturesJava language for Internet environment, is a widely used web programming language, it has the following features:SimpleJava language and C + + syntax rules are similar, but canceled the Java language and multiple inheritance pointer, unified by reference to indicate the object (C + + in two forms, is actually two ways to generate objects, and Java, there is only one) by automatic garbagecollection eliminates the need for programmers working for the release of the memory block.object-oriented (nearly complete)Java language in order to improve efficiency, defined a few basic data types to achieve a non-class manner, and the remaining class of all data types in the form of packaging, the program structure of the system unit is also a class. Therefore considered to be almost completely object-oriented.platform independent (portable, cross-platform)Java Virtual Machine (JVM) is true in a variety of machine architectures implemented using software to simulate an imaginary machine, when necessary, can be implemented by hardware.Of course, the internal implementation of these virtual machines vary, but its function is the same - the implementation of a unified Java virtual machine instructions.Java compiler Java application's source code files (. Java) translated into Java byte code file (. Class), which is composed of Java virtual machine instructions. Because it is a virtual machine, and thus the implementation of Java Virtual Machine Java programs commonly referred to as the process of interpretation.Relies on virtual machine technology, Java language has nothing todo with the characteristics of the machine architecture, that Java programs, once after being written, can be transplanted without modification to any one on a different machine architecture. From theoperating system point of view, the process of implementation of a Java program is the process of implementation of a Java virtual machine process.oriented network programmingJava language for generating the beginning of the network of supportin the JDK includes TCP / IP, HTTP and FTP protocols such as class libraries.Multi-threading supportMultithreading is to simultaneously perform multiple tasks of a function. Multi-threading mechanism that enables applications to perform multiple tasks in parallel, the various thread synchronization mechanisms to ensure proper operation of the shared data.Good security codeRuntime (Runtime) term perspective emphasizes the dynamic process of the dynamic changes when the program is running, but also with the expression of the runtime environment similar to the meaning of the word.Java technology is a lot of work done at run time, such as strengthening security code verification operations.In general, Java technology runtime environment performs thefollowing three major tasks:loading code - the implementation by the class loaderClass loader for the implementation of the procedures required toload all classes (as far as possible and not necessarily the same).validation code - the implementation of the byte code verifierJava code before the actual operation after several tests. Byte code verifier for four times on the validation code, which can ensure code compliance and does not destroy the JVM specification system integrity.If - Check forged pointers, object access rights violation or attempt to change the object type of illegal code.code execution - from the implementation of the runtime interpreterAutomatic garbage collectionMany programming languages allow programs running in the memoryblock dynamically allocated, the process of allocating memory blocks because of the language syntax varies, but always point to the store to return to the starting position of the pointer. In C, C + + and other languages, the programmer is responsible for deallocation of memory blocks. Sometimes this is a very difficult task. Because programmers do not always know in advance when a block of memory should be released. When not in the system can be allocated memory block, it can cause the program to a standstill, this procedure is called a memory leak.When the allocated memory block is no longer needed, the programshould be canceled or the operating environment to allocate memory block.garbage collection is no longer needed recovery of allocated memory block. In other languages in general, is the programmer's responsibility to cancel the allocation.Java programming language provides a system-level threads to keep track of memory allocation, to complete the garbage collection:No longer need to check and release the memory block,The above work can be completed automatically,In the JVM implementation cycle, resulting in unexpected changes,Good robustness of the code.Java program to check at compile and run-time errors. Type of examination can help detect many errors early in development. Meanwhile, many integrated development tools (IDE) to compile and run the emergence of Java programs easier and a lot of integrated development tools (eg Eclipse) are free.2 Object-oriented and process-oriented differencesThe production of a programming language, programming is not only a technical improvement, but also includes the expression of ideas andcognitive progress. The C language as the representative of the early part of the language, known asprocess-oriented language, not only because of their expression of program design is based on the basic elements of the process, in essence, is now more understanding of the computerized system the dominant ideology or control flow or data flow, constitute elements of the system is the module - processing logic.The generation of object-oriented languages, because the understanding of the system or the abstract to a more advanced level. Cognitive thinking at this time not only closer to the real world, andits high degree of abstraction. Thus, both easy to understand on the one hand, there are also difficult to understand the other hand, to see the realm of understanding.2.1 Review process-oriented thinkingProcess-oriented programming language, thought and expression, canbe simply summarized as the following few:Understanding of the system structure analysis of the process - top-down, stepwise refinement to the functional decomposition;Each function is a data processing module, which fully describe the IPO described the internal and external features of the module;Each module is control flow, and therefore have a typical structureof the three procedures - sequence, branch, loop;The relationship between the module by calling the preserve, which has become a function module, which is the most important process-oriented way of code reuse under way;Although the function call parameters and return values, but thedata and functions are always separate, not only with the famous assertion - program = algorithm + data, but also makes the absolute equality of the disorder have trouble - all the functions and data relationship is no limit;If you want to use the data flow, then the data can only be produced in an appropriate time after the call function.The main drawback of this period are: understanding the system more difficult, the systematic development of low efficiency, codereusability is poor.2.2 OOPObject-oriented thinking on the use of an intuitive understanding of the real world, when the use of computerized depth of abstraction can be summarized briefly as follows: System is composed of things, there is a connection between things, the complexity is system;System and the system, and things, things and things is a clear boundary between the (boundary) of;System or the state of things can describe the property, said property is usually some simple data, if that is something the complex;System or the state of things will change, called the behavior of a difference there is a reason (internal or external), changes in the process may be complex;Will have different things in common between the properties and behavior, a common extreme case is completely contained.Based on the above understanding, a runtime (dynamic) to thespecific system or something, by several smaller things that constitute a specific (extreme things is a simpleattribute data), which is constantly changing. If this concept of things an effective abstract, then the problem is solved.First of all, any one specific thing called the object (Object), it is the extreme case of previous variables; things are classified, each class of things have the properties and behavior of uniform, that type - abstract data types, referred to as for the class (Class); behavior since it is the process, then a function of the abstract, named for the method to show the difference.For example:Describe the height or name, each just a simple data variable;Describe a student, you can use the student number, name, dorm, class, etc.; What kind of accommodation that replaced it!It describes the dorm, class, and also has many projects.3 Object-oriented programming concepts and features of the mainObject-oriented programming (Object Oriented Programming, OOP) language, in order to be more highly abstract, will introduce some ofthe real world, the concept is difficult to find, but for a programming language is indeed valuable. The following describes the concept ofbeing basically derived from the abstract to the real world, from therole of program design to understand them.Object-oriented programming to make the system easier to understand, but also make the code better reusability, scalability, easy management and maintenance.3.1 Main Concepts(1) classClass is the abstract of a class of things that the data type is equivalent to its role, of course, can be regarded as complex data types. Such as students, dormitories, class. (2) the objectObject represents a specific thing, its role is variable, that is, a complex data type - xx class variables. Such as Zhou Yu, Zhang Fei, Yufly home, Tiger classes. (3) membersThe elements of a thing to discuss when the class is virtual, it is the discussion of specific objects. As in class, a variable belonging to members - member variable, an object also belong to members - members of the object, a function also belong to the members - members of the method.3.2 Main FeaturesThere are three features of OOP languages: encapsulation,inheritance and polymorphism.(1) packageThe composition includes members of the class variables / objects and members of the method, so the relevant data and functions will be packaged together with other distinguished class is package. Obviously, avoiding the process-oriented parallel language defects, indicating the class and members of their respective relationships. Further, members of the class can limit the visibility of the external, then the packagewill reflect the more perfect.(2) inheritanceWhen a thing is another thing entirely a special case of B, then, in general, the class Aclass B is more than the number of member variables / objects and members of the method, called class A inherits class B and class A is called ( Class B's) sub-class, class B is called (Class A) for the parent class.Parent, also known as the base class, superclass, subclass, also known as derived class, derived class.Obviously there is no need to write duplicate subclass the parent class to write some code in Part B, which is the most typical OOP code reuse.(3) multi-statePolymorphism that an act of a class there are several implementation version. The simplest case is in a class, given a variety of different implementations, the complex is in many different sub-classes are given in their implementation.。