深入理解Java泛型与集合

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"Java泛型和集合，英文原版，由Maurice Naftalin和Philip Wadler合著，O'Reilly Media出版。本书详细介绍了Java泛型和集合的使用，是学习Java泛型的优秀参考资料。" 在Java编程语言中，泛型和集合是两个极其重要的概念，它们共同提升了代码的类型安全性和可读性。Java泛型是在JDK 5.0版本引入的，其主要目标是允许在编译时检查类型，防止在运行时出现ClassCastException。这通过引入类型参数化来实现，使得集合可以存储特定类型的元素，而不是任何Object。泛型的主要特点包括： 1. 类型安全：通过泛型，编译器可以在编译时就发现类型错误，避免了运行时异常。 2. 消除强制类型转换：在使用泛型之前，从集合中取出对象需要进行强制类型转换，而泛型集合可以直接使用预期类型，无需转换。 3. 提高代码复用：泛型允许创建通用的类、接口和方法，适用于多种数据类型，减少了代码重复。 Java集合框架包括List、Set、Queue等接口，以及ArrayList、HashSet、LinkedList等实现类。泛型的应用使集合框架更加灵活和强大。例如，ArrayList<T>可以确保列表中的所有元素都是类型T，不允许插入其他类型。本书《Java Generics and Collections》详细探讨了以下主题： 1. 泛型的基本概念：类型参数、类型通配符、类型推断、边界限制（如extends和super关键字）。 2. 集合接口：List、Set、Map及其子接口的泛型使用。 3. 泛型与反射、序列化的关系。 4. 泛型方法和泛型类型的创建。 5. 类级和方法级的类型参数，以及泛型通配符在多态中的应用。 6. 实际编程中的最佳实践和陷阱，以及如何避免类型擦除带来的问题。 7. 深入讨论了Java集合框架的设计和实现，包括内部工作原理和性能优化。作者Maurice Naftalin和Philip Wadler是Java泛型和集合领域的专家，他们通过丰富的实例和深入的分析，帮助读者理解和掌握这些核心概念。书中的内容涵盖了从基础到高级的泛型和集合使用，适合各层次的Java开发者阅读。 Java泛型和集合是Java开发中不可或缺的部分，理解并熟练运用它们可以显著提高代码质量。这本书提供了一个全面的学习指南，对于想要提升Java编程技能的开发者来说是一份宝贵的资源。

• We often include code that corresponds to the body of an appropriate main method:

Stack<Integer> stack = new ArrayStack<Integer>();

for (int i = 0; i<4; i++) stack.push(i);

assert stack.toString().equals("stack[0, 1, 2, 3]");

• Code fragments are printed in fixed-width font when they appear within a para-

graph (as when we referred to a main method in the preceding item).

• We often omit standard imports. Code that uses the Java Collection Framework

or other utility classes should be preceded by the line:

import java.util.*;

• Sample interactive sessions, showing command-line input and corresponding out-

put, are shown in constant-width font, with user-supplied input preceded by a

percent sign:

% javac g/Stack.java g/ArrayStack.java g/Stacks.java l/Client.java

Note: Client.java uses unchecked or unsafe operations.

Note: Recompile with -Xlint:unchecked for details.

• When user-supplied input is two lines long, the first line is ended with a backslash:

% javac -Xlint:unchecked g/Stack.java g/ArrayStack.java \

% g/Stacks.java l/Client.java

l/Client.java:4: warning: [unchecked] unchecked call

to push(E) as a member of the raw type Stack

for (int i = 0; i<4; i++) stack.push(new Integer(i));

Using Code Examples

This book is here to help you get your job done. In general, you may use the code in

this book in your programs and documentation. You do not need to contact us for

permission unless you’re reproducing a significant portion of the code. For example,

writing a program that uses several chunks of code from this book does not require

permission. Selling or distributing a CD-ROM of examples from O’Reilly books does

require permission. Answering a question by citing this book and quoting example

code does not require permission. Incorporating a significant amount of example code

from this book into your product’s documentation does require permission.

We appreciate, but do not require, attribution. An attribution usually includes the title,

author, publisher, and ISBN. For example: "Java Generics and Collections, by Maurice

If you feel your use of code examples falls outside fair use or the permission given above,

feel free to contact us at permissions@oreilly.com.

xiv | Preface

PART I

Generics

Generics are a powerful, and sometimes controversial, new feature of the Java pro-

gramming language. This part of the book describes generics, using the Collections

Framework as a source of examples. A comprehensive introduction to the Collections

Framework appears in the second part of the book.

The first five chapters focus on the fundamentals of generics. Chapter 1 gives an over-

view of generics and other new features in Java 5, including boxing, foreach loops, and

functions with a variable number of arguments. Chapter 2 reviews how subtyping

works and explains how wildcards let you use subtyping in connection with generics.

Chapter 3 describes how generics work with the Comparable interface, which requires

a notion of bounds on type variables. Chapter 4 looks at how generics work with various

declarations, including constructors, static members, and nested classes. Chapter 5

explains how to evolve legacy code to exploit generics, and how ease of evolution is a

key advantage of the design of generics in Java. Once you have these five chapters under

your belt, you will be able to use generics effectively in most basic situations.

The next four chapters treat advanced topics. Chapter 6 explains how the same design

that leads to ease of evolution also necessarily leads to a few rough edges in the treat-

ment of casts, exceptions, and arrays. The fit between generics and arrays is the worst

rough corner of the language, and we formulate two principles to help you work around

the problems. Chapter 7 explains new features that relate generics and reflection, in-

cluding the newly generified type Class<T> and additions to the Java library that support

reflection of generic types. Chapter 8 contains advice on how to use generics effectively

in practical coding. We consider checked collections, security issues, specialized

classes, and binary compatibility. Chapter 9 presents five extended examples, looking

at how generics affect five well-known design patterns: Visitor, Interpreter, Function,

Strategy, and Subject-Observer.

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