## Chapter 9. General Programming（通用程序设计）
### Item 68: Adhere to generally accepted naming conventions（遵守被广泛认可的命名约定）
The Java platform has a well-established set of naming conventions, many of which are contained in The Java Language Specification [JLS, 6.1]. Loosely speaking, naming conventions fall into two categories: typographical and grammatical.
Java 平台有一组完善的命名约定，其中许多约定包含在《The Java Language Specification》[JLS, 6.1]。不严格地讲，命名约定分为两类：排版和语法。
There are only a handful of typographical naming conventions, covering packages, classes, interfaces, methods, fields, and type variables. You should rarely violate them and never without a very good reason. If an API violates these conventions, it may be difficult to use. If an implementation violates them, it may be difficult to maintain. In both cases, violations have the potential to confuse and irritate other programmers who work with the code and can cause faulty assumptions that lead to errors. The conventions are summarized in this item.
有少量的与排版有关的命名约定，包括包、类、接口、方法、字段和类型变量。如果没有很好的理由，你不应该违反它们。如果 API 违反了这些约定，那么它可能很难使用。如果实现违反了这些规则，可能很难维护。在这两种情况下，违规都有可能使其他使用代码的程序员感到困惑和恼怒，并使他们做出错误的假设，从而导致错误。本条目概述了各项约定。
Package and module names should be hierarchical with the components separated by periods. Components should consist of lowercase alphabetic characters and, rarely, digits. The name of any package that will be used outside your organization should begin with your organization’s Internet domain name with the components reversed, for example, edu.cmu, com.google, org.eff. The standard libraries and optional packages, whose names begin with java and javax, are exceptions to this rule. Users must not create packages or modules whose names begin with java or javax. Detailed rules for converting Internet domain names to package name prefixes can be found in the JLS [JLS, 6.1].
包名和模块名应该是分层的，组件之间用句点分隔。组件应该由小写字母组成，很少使用数字。任何在你的组织外部使用的包，名称都应该以你的组织的 Internet 域名开头，并将组件颠倒过来，例如，edu.cmu、com.google、org.eff。以 java 和 javax 开头的标准库和可选包是这个规则的例外。用户不能创建名称以 java 或 javax 开头的包或模块。将 Internet 域名转换为包名前缀的详细规则可以在《The Java Language Specification》[JLS, 6.1] 中找到。
The remainder of a package name should consist of one or more components describing the package. Components should be short, generally eight or fewer characters. Meaningful abbreviations are encouraged, for example, util rather than utilities. Acronyms are acceptable, for example, awt. Components should generally consist of a single word or abbreviation.
包名的其余部分应该由描述包的一个或多个组件组成。组件应该很短，通常为 8 个或更少的字符。鼓励使用有意义的缩写，例如 util 而不是 utilities。缩写词是可以接受的，例如 awt。组件通常应该由一个单词或缩写组成。
Many packages have names with just one component in addition to the Internet domain name. Additional components are appropriate for large facilities whose size demands that they be broken up into an informal hierarchy. For example, the javax.util package has a rich hierarchy of packages with names such as java.util.concurrent.atomic. Such packages are known as subpackages, although there is almost no linguistic support for package hierarchies.
除了 Internet 域名之外，许多包的名称只有一个组件。附加组件适用于大型工具包，这些工具包的大小要求将其分解为非正式的层次结构。例如 `javax.util` 包具有丰富的包层次结构，包的名称如 `java.util.concurrent.atomic`。这样的包称为子包，尽管 Java 几乎不支持包层次结构。
Class and interface names, including enum and annotation type names, should consist of one or more words, with the first letter of each word capitalized, for example, List or FutureTask. Abbreviations are to be avoided, except for acronyms and certain common abbreviations like max and min. There is some disagreement as to whether acronyms should be uppercase or have only their first letter capitalized. While some programmers still use uppercase, a strong argument can be made in favor of capitalizing only the first letter: even if multiple acronyms occur back-to-back, you can still tell where one word starts and the next word ends. Which class name would you rather see, HTTPURL or HttpUrl?
类和接口名称，包括枚举和注释类型名称，应该由一个或多个单词组成，每个单词的首字母大写，例如 List 或 FutureTask。除了缩略语和某些常见的缩略语，如 max 和 min，缩略语应该避免使用。缩略语应该全部大写，还是只有首字母大写，存在一些分歧。虽然有些程序员仍然使用大写字母，但支持只将第一个字母大写的理由很充分：即使多个首字母缩写连续出现，你仍然可以知道一个单词从哪里开始，下一个单词从哪里结束。你希望看到哪个类名，HTTPURL 还是 HttpUrl？
Method and field names follow the same typographical conventions as class and interface names, except that the first letter of a method or field name should be lowercase, for example, remove or ensureCapacity. If an acronym occurs as the first word of a method or field name, it should be lowercase.
方法和字段名遵循与类和接口名相同的排版约定，除了方法或字段名的第一个字母应该是小写，例如 remove 或 ensureCapacity。如果方法或字段名的首字母缩写出现在第一个单词中，那么它应该是小写的。
The sole exception to the previous rule concerns “constant fields,” whose names should consist of one or more uppercase words separated by the underscore character, for example, VALUES or NEGATIVE_INFINITY. A constant field is a static final field whose value is immutable. If a static final field has a primitive type or an immutable reference type (Item 17), then it is a constant field. For example, enum constants are constant fields. If a static final field has a mutable reference type, it can still be a constant field if the referenced object is immutable. Note that constant fields constitute the only recommended use of underscores.
前面规则的唯一例外是「常量字段」，它的名称应该由一个或多个大写单词组成，由下划线分隔，例如 VALUES 或 NEGATIVE_INFINITY。常量字段是一个静态的 final 字段，其值是不可变的。如果静态 final 字段具有基本类型或不可变引用类型(第17项)，那么它就是常量字段。例如，枚举常量是常量字段。如果静态 final 字段有一个可变的引用类型，那么如果所引用的对象是不可变的，那么它仍然可以是一个常量字段。注意，常量字段是唯一推荐使用下划线用法的。
Local variable names have similar typographical naming conventions to member names, except that abbreviations are permitted, as are individual characters and short sequences of characters whose meaning depends on the context in which they occur, for example, i, denom, houseNum. Input parameters are a special kind of local variable. They should be named much more carefully than ordinary local variables, as their names are an integral part of their method’s documentation.
局部变量名与成员名具有类似的排版命名约定，但允许使用缩写，也允许使用单个字符和短字符序列，它们的含义取决于它们出现的上下文，例如 i、denom、houseNum。输入参数是一种特殊的局部变量。它们的命名应该比普通的局部变量谨慎得多，因为它们的名称是方法文档的组成部分。
Type parameter names usually consist of a single letter. Most commonly it is one of these five: T for an arbitrary type, E for the element type of a collection, K and V for the key and value types of a map, and X for an exception. The return type of a function is usually R. A sequence of arbitrary types can be T, U, V or T1, T2, T3.
类型参数名通常由单个字母组成。最常见的是以下五种类型之一：T 表示任意类型，E 表示集合的元素类型，K 和 V 表示 Map 的键和值类型，X 表示异常。函数的返回类型通常为 R。任意类型的序列可以是 T、U、V 或 T1、T2、T3。
For quick reference, the following table shows examples of typographical conventions.
为了快速参考，下表显示了排版约定的示例。
| Identifier Type | Example |
|:-------:|:-------:|
| Package or module | `org.junit.jupiter.api`, `com.google.common.collect` |
| Class or Interface | Stream, FutureTask, LinkedHashMap,HttpClient |
| Method or Field | remove, groupingBy, getCrc |
| Constant Field | MIN_VALUE, NEGATIVE_INFINITY |
| Local Variable | i, denom, houseNum |
| Type Parameter | T, E, K, V, X, R, U, V, T1, T2 |
Grammatical naming conventions are more flexible and more controversial than typographical conventions. There are no grammatical naming conventions to speak of for packages. Instantiable classes, including enum types, are generally named with a singular noun or noun phrase, such as Thread, PriorityQueue, or ChessPiece. Non-instantiable utility classes (Item 4) are often named with a plural noun, such as Collectors or Collections. Interfaces are named like classes, for example, Collection or Comparator, or with an adjective ending in able or ible, for example, Runnable, Iterable, or Accessible. Because annotation types have so many uses, no part of speech predominates. Nouns, verbs, prepositions, and adjectives are all common, for example, BindingAnnotation, Inject, ImplementedBy, or Singleton.
语法命名约定比排版约定更灵活，也更有争议。包没有语法命名约定。可实例化的类，包括枚举类型，通常使用一个或多个名词短语来命名，例如 Thread、PriorityQueue 或 ChessPiece。不可实例化的实用程序类（[Item-4](/Chapter-2/Chapter-2-Item-4-Enforce-noninstantiability-with-a-private-constructor.md)）通常使用复数名词来命名，例如 collector 或 Collections。接口的名称类似于类，例如集合或比较器，或者以 able 或 ible 结尾的形容词，例如 Runnable、Iterable 或 Accessible。因为注解类型有很多的用途，所以没有哪部分占主导地位。名词、动词、介词和形容词都很常见，例如，BindingAnnotation、Inject、ImplementedBy 或 Singleton。
Methods that perform some action are generally named with a verb or verb phrase (including object), for example, append or drawImage. Methods that return a boolean value usually have names that begin with the word is or, less commonly, has, followed by a noun, noun phrase, or any word or phrase that functions as an adjective, for example, isDigit, isProbablePrime, isEmpty, isEnabled, or hasSiblings.
执行某些操作的方法通常用动词或动词短语（包括对象）命名，例如，append 或 drawImage。返回布尔值的方法的名称通常以单词 is 或 has（通常很少用）开头，后面跟一个名词、一个名词短语，或者任何用作形容词的单词或短语，例如 isDigit、isProbablePrime、isEmpty、isEnabled 或 hasSiblings。
Methods that return a non-boolean function or attribute of the object on which they’re invoked are usually named with a noun, a noun phrase, or a verb phrase beginning with the verb get, for example, size, hashCode, or getTime. There is a vocal contingent that claims that only the third form (beginning with get) is acceptable, but there is little basis for this claim. The first two forms usually lead to more readable code, for example:
返回被调用对象的非布尔函数或属性的方法通常使用以 get 开头的名词、名词短语或动词短语来命名，例如 size、hashCode 或 getTime。有一种说法是，只有第三种形式（以 get 开头）才是可接受的，但这种说法几乎没有根据。前两种形式的代码通常可读性更强，例如：
```
if (car.speed() > 2 * SPEED_LIMIT)
generateAudibleAlert("Watch out for cops!");
```
The form beginning with get has its roots in the largely obsolete Java Beans specification, which formed the basis of an early reusable component architecture. There are modern tools that continue to rely on the Beans naming convention, and you should feel free to use it in any code that is to be used in conjunction with these tools. There is also a strong precedent for following this naming convention if a class contains both a setter and a getter for the same attribute. In this case, the two methods are typically named getAttribute and setAttribute.
以 get 开头的表单起源于基本过时的 Java bean 规范，该规范构成了早期可复用组件体系结构的基础。有一些现代工具仍然依赖于 bean 命名约定，你应该可以在任何与这些工具一起使用的代码中随意使用它。如果类同时包含相同属性的 setter 和 getter，则遵循这种命名约定也有很好的先例。在本例中，这两个方法通常被命名为 getAttribute 和 setAttribute。
A few method names deserve special mention. Instance methods that convert the type of an object, returning an independent object of a different type, are often called toType, for example, toString or toArray. Methods that return a view (Item 6) whose type differs from that of the receiving object are often called asType, for example, asList. Methods that return a primitive with the same value as the object on which they’re invoked are often called typeValue, for example, intValue. Common names for static factories include from, of, valueOf, instance, getInstance, newInstance, getType, and newType (Item 1, page 9).
一些方法名称值得特别注意。转换对象类型（返回不同类型的独立对象）的实例方法通常称为 toType，例如 toString 或 toArray。返回与接收对象类型不同的视图（[Item-6](/Chapter-2/Chapter-2-Item-6-Avoid-creating-unnecessary-objects.md)）的方法通常称为 asType，例如 asList。返回与调用它们的对象具有相同值的基本类型的方法通常称为类型值，例如 intValue。静态工厂的常见名称包括 from、of、valueOf、instance、getInstance、newInstance、getType 和 newType（[Item-1](/Chapter-2/Chapter-2-Item-1-Consider-static-factory-methods-instead-of-constructors.md)，第 9 页）。
Grammatical conventions for field names are less well established and less important than those for class, interface, and method names because welldesigned APIs contain few if any exposed fields. Fields of type boolean are often named like boolean accessor methods with the initial is omitted, for example, initialized, composite. Fields of other types are usually named with nouns or noun phrases, such as height, digits, or bodyStyle. Grammatical conventions for local variables are similar to those for fields but even weaker.
字段名的语法约定没有类、接口和方法名的语法约定建立得好，也不那么重要，因为设计良好的 API 包含很少的公开字段。类型为 boolean 的字段的名称通常类似于 boolean 访问器方法，省略了初始值「is」，例如 initialized、composite。其他类型的字段通常用名词或名词短语来命名，如 height、digits 和 bodyStyle。局部变量的语法约定类似于字段的语法约定，但要求更少。
To summarize, internalize the standard naming conventions and learn to use them as second nature. The typographical conventions are straightforward and largely unambiguous; the grammatical conventions are more complex and looser. To quote from The Java Language Specification [JLS, 6.1], “These conventions should not be followed slavishly if long-held conventional usage dictates otherwise.” Use common sense.
总之，将标准命名约定内在化，并将其作为第二性征来使用。排版习惯是直接的，而且在很大程度上是明确的；语法惯例更加复杂和松散。引用《The JavaLanguage Specification》[JLS, 6.1] 中的话说，「如果长期以来的传统用法要求不遵循这些约定，就不应该盲目地遵循这些约定。」，应使用常识判断。
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- Chapter 2. Creating and Destroying Objects（创建和销毁对象）
- Item 1: Consider static factory methods instead of constructors（考虑以静态工厂方法代替构造函数）
- Item 2: Consider a builder when faced with many constructor parameters（在面对多个构造函数参数时，请考虑构建器）
- Item 3: Enforce the singleton property with a private constructor or an enum type（使用私有构造函数或枚举类型实施单例属性）
- Item 4: Enforce noninstantiability with a private constructor（用私有构造函数实施不可实例化）
- Item 5: Prefer dependency injection to hardwiring resources（依赖注入优于硬连接资源）
- Item 6: Avoid creating unnecessary objects（避免创建不必要的对象）
- Item 7: Eliminate obsolete object references（排除过时的对象引用）
- Item 8: Avoid finalizers and cleaners（避免使用终结器和清除器）
- Item 9: Prefer try with resources to try finally（使用 try-with-resources 优于 try-finally）
- Chapter 3. Methods Common to All Objects（对象的通用方法）
- Item 10: Obey the general contract when overriding equals（覆盖 equals 方法时应遵守的约定）
- Item 11: Always override hashCode when you override equals（当覆盖 equals 方法时，总要覆盖 hashCode 方法）
- Item 12: Always override toString（始终覆盖 toString 方法）
- Item 13: Override clone judiciously（明智地覆盖 clone 方法）
- Item 14: Consider implementing Comparable（考虑实现 Comparable 接口）
- Chapter 4. Classes and Interfaces（类和接口）
- Item 15: Minimize the accessibility of classes and members（尽量减少类和成员的可访问性）
- Item 16: In public classes use accessor methods not public fields（在公共类中，使用访问器方法，而不是公共字段）
- Item 17: Minimize mutability（减少可变性）
- Item 18: Favor composition over inheritance（优先选择复合而不是继承）
- Item 19: Design and document for inheritance or else prohibit it（继承要设计良好并且具有文档，否则禁止使用）
- Item 20: Prefer interfaces to abstract classes（接口优于抽象类）
- Item 21: Design interfaces for posterity（为后代设计接口）
- Item 22: Use interfaces only to define types（接口只用于定义类型）
- Item 23: Prefer class hierarchies to tagged classes（类层次结构优于带标签的类）
- Item 24: Favor static member classes over nonstatic（静态成员类优于非静态成员类）
- Item 25: Limit source files to a single top level class（源文件仅限有单个顶层类）
- Chapter 5. Generics（泛型）
- Item 26: Do not use raw types（不要使用原始类型）
- Item 27: Eliminate unchecked warnings（消除 unchecked 警告）
- Item 28: Prefer lists to arrays（list 优于数组）
- Item 29: Favor generic types（优先使用泛型）
- Item 30: Favor generic methods（优先使用泛型方法）
- Item 31: Use bounded wildcards to increase API flexibility（使用有界通配符增加 API 的灵活性）
- Item 32: Combine generics and varargs judiciously（明智地合用泛型和可变参数）
- Item 33: Consider typesafe heterogeneous containers（考虑类型安全的异构容器）
- Chapter 6. Enums and Annotations（枚举和注解）
- Item 34: Use enums instead of int constants（用枚举类型代替 int 常量）
- Item 35: Use instance fields instead of ordinals（使用实例字段替代序数）
- Item 36: Use EnumSet instead of bit fields（用 EnumSet 替代位字段）
- Item 37: Use EnumMap instead of ordinal indexing（使用 EnumMap 替换序数索引）
- Item 38: Emulate extensible enums with interfaces（使用接口模拟可扩展枚举）
- Item 39: Prefer annotations to naming patterns（注解优于命名模式）
- Item 40: Consistently use the Override annotation（坚持使用 @Override 注解）
- Item 41: Use marker interfaces to define types（使用标记接口定义类型）
- Chapter 7. Lambdas and Streams（λ 表达式和流）
- Item 42: Prefer lambdas to anonymous classes（λ 表达式优于匿名类）
- Item 43: Prefer method references to lambdas（方法引用优于 λ 表达式）
- Item 44: Favor the use of standard functional interfaces（优先使用标准函数式接口）
- Item 45: Use streams judiciously（明智地使用流）
- Item 46: Prefer side effect free functions in streams（在流中使用无副作用的函数）
- Item 47: Prefer Collection to Stream as a return type（优先选择 Collection 而不是流作为返回类型）
- Item 48: Use caution when making streams parallel（谨慎使用并行流）
- Chapter 8. Methods（方法）
- Item 49: Check parameters for validity（检查参数的有效性）
- Item 50: Make defensive copies when needed（在需要时制作防御性副本）
- Item 51: Design method signatures carefully（仔细设计方法签名）
- Item 52: Use overloading judiciously（明智地使用重载）
- Item 53: Use varargs judiciously（明智地使用可变参数）
- Item 54: Return empty collections or arrays, not nulls（返回空集合或数组，而不是 null）
- Item 55: Return optionals judiciously（明智地的返回 Optional）
- Item 56: Write doc comments for all exposed API elements（为所有公开的 API 元素编写文档注释）
- Chapter 9. General Programming（通用程序设计）
- Item 57: Minimize the scope of local variables（将局部变量的作用域最小化）
- Item 58: Prefer for-each loops to traditional for loops（for-each 循环优于传统的 for 循环）
- Item 59: Know and use the libraries（了解并使用库）
- Item 60: Avoid float and double if exact answers are required（若需要精确答案就应避免使用 float 和 double 类型）
- Item 61: Prefer primitive types to boxed primitives（基本数据类型优于包装类）
- Item 62: Avoid strings where other types are more appropriate（其他类型更合适时应避免使用字符串）
- Item 63: Beware the performance of string concatenation（当心字符串连接引起的性能问题）
- Item 64: Refer to objects by their interfaces（通过接口引用对象）
- Item 65: Prefer interfaces to reflection（接口优于反射）
- Item 66: Use native methods judiciously（明智地使用本地方法）
- Item 67: Optimize judiciously（明智地进行优化）
- Item 68: Adhere to generally accepted naming conventions（遵守被广泛认可的命名约定）
- Chapter 10. Exceptions（异常）
- Item 69: Use exceptions only for exceptional conditions（仅在确有异常条件下使用异常）
- Item 70: Use checked exceptions for recoverable conditions and runtime exceptions for programming errors（对可恢复情况使用 checked 异常，对编程错误使用运行时异常）
- Item 71: Avoid unnecessary use of checked exceptions（避免不必要地使用 checked 异常）
- Item 72: Favor the use of standard exceptions（鼓励复用标准异常）
- Item 73: Throw exceptions appropriate to the abstraction（抛出能用抽象解释的异常）
- Item 74: Document all exceptions thrown by each method（为每个方法记录会抛出的所有异常）
- Item 75: Include failure capture information in detail messages（异常详细消息中应包含捕获失败的信息）
- Item 76: Strive for failure atomicity（尽力保证故障原子性）
- Item 77: Don’t ignore exceptions（不要忽略异常）
- Chapter 11. Concurrency（并发）
- Item 78: Synchronize access to shared mutable data（对共享可变数据的同步访问）
- Item 79: Avoid excessive synchronization（避免过度同步）
- Item 80: Prefer executors, tasks, and streams to threads（Executor、task、流优于直接使用线程）
- Item 81: Prefer concurrency utilities to wait and notify（并发实用工具优于 wait 和 notify）
- Item 82: Document thread safety（文档应包含线程安全属性）
- Item 83: Use lazy initialization judiciously（明智地使用延迟初始化）
- Item 84: Don’t depend on the thread scheduler（不要依赖线程调度器）
- Chapter 12. Serialization（序列化）
- Item 85: Prefer alternatives to Java serialization（优先选择 Java 序列化的替代方案）
- Item 86: Implement Serializable with great caution（非常谨慎地实现 Serializable）
- Item 87: Consider using a custom serialized form（考虑使用自定义序列化形式）
- Item 88: Write readObject methods defensively（防御性地编写 readObject 方法）
- Item 89: For instance control, prefer enum types to readResolve（对于实例控制，枚举类型优于 readResolve）
- Item 90: Consider serialization proxies instead of serialized instances（考虑以序列化代理代替序列化实例）