精通Java 7多线程开发：并行指南

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"Java 7 并行指南书" 本书《Java 7 并行指南书》专注于通过60多个简洁而高效的方法，帮助读者掌握Java 7中的多线程应用程序开发。作者Javier Fernández González是一位经验丰富的IT专家，他深入浅出地介绍了Java 7在并行处理领域的关键概念和技术。 Java 7引入了若干重要的并发编程改进，旨在提高多线程应用的性能和可维护性。以下是一些关键知识点： 1. **Fork/Join框架**：这是Java 7中一个重要的新特性，它提供了一种处理大型计算任务的有效方式。Fork/Join框架基于分治策略，将大任务分解为小任务，然后在工作窃取队列中执行这些子任务，从而实现并行计算。 2. **并发集合类的增强**：Java 7对`ConcurrentHashMap`进行了优化，提升了并发性能。此外，还引入了`ConcurrentSkipListMap`，这是一种线程安全的有序映射，适用于需要保持排序顺序的并发场景。 3. **原子变量类（Atomic Variables）**：Java 7提供了更多的原子变量类，如`AtomicIntegerArray`、`AtomicLongArray`等，它们支持低开销的无锁编程，可以用于在多线程环境中更新数组元素。 4. **ThreadLocalRandom**：为了提高多线程环境下的随机数生成性能，Java 7引入了`ThreadLocalRandom`类，每个线程都有自己的随机数生成器实例，减少了同步开销。 5. **try-with-resources语句**：这个语法糖使得资源管理（如文件、数据库连接等）变得更加方便和安全，尤其是在多线程环境中，确保资源在使用完毕后被正确关闭，避免资源泄漏。 6. **改进的死锁检测**：Java 7的JDK工具如`jstack`提供了更好的死锁检测和分析能力，帮助开发者诊断和解决多线程程序中的死锁问题。 7. **更强大的并发工具类**：`java.util.concurrent`包中新增了一些实用工具类，如`CountDownLatch`、`CyclicBarrier`和`Phaser`，这些工具可以帮助开发者更好地控制线程间的同步和协调。 8. **更易用的线程池API**：`ExecutorService`和`ThreadPoolExecutor`类的使用更加简便，允许开发者创建和管理线程池，以便更有效地调度和执行任务。 9. **线程本地存储（ThreadLocal）的改进**：`ThreadLocal`类在Java 7中增强了对内存泄漏的防护，当线程结束时，会自动清理其关联的`ThreadLocal`变量。 10. **异常处理优化**：在多线程环境中，Java 7改进了异常处理机制，使得在捕获和处理异常时，程序的行为更加清晰和一致。《Java 7 并行指南书》全面覆盖了Java 7在并行编程方面的核心特性，是开发者理解和应用这些技术的重要参考资料。通过学习本书，读者能够更好地设计和实现高效的多线程应用，提升软件性能，同时减少潜在的并发问题。

Preface

Who this book is for

If you are a Java developer, who wants to take his knowledge of concurrent programming and

multithreading further, as well as discover the new concurrency features of Java 7, then Java

7 Concurrency Cookbook is for you. You should already be comfortable with general Java

development practices and a basic grasp of threads would be an advantage.

Conventions

In this book, you will nd a number of styles of text that distinguish between different kinds

of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text are shown as follows: “Extending the Thread class and overriding the

run() method”.

A block of code is set as follows:

public Calculator(int number) {

this.number=number;

}

New terms and important words are shown in bold. Words that you see on the screen,

in menus or dialog boxes for example, appear in the text like this: “Create a new project

with the New Project option of the File menu in the menu bar”.

Warnings or important notes appear in a box like this.

Tips and tricks appear like this.

Reader feedback

Feedback from our readers is always welcome. Let us know what you think about this

book—what you liked or may have disliked. Reader feedback is important for us to develop

titles that you really get the most out of.

To send us general feedback, simply send an e-mail to feedback@packtpub.com, and

mention the book title via the subject of your message.

Preface

If there is a topic that you have expertise in and you are interested in either writing

or contributing to a book, see our author guide on www.packtpub.com/authors.

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Now that you are the proud owner of a Packt book, we have a number of things to help you

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Downloading the example code

You can download the example code les for all Packt books you have purchased from your

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Errata

Although we have taken every care to ensure the accuracy of our content, mistakes

do happen. If you nd a mistake in one of our books—maybe a mistake in the text or the

code—we would be grateful if you would report this to us. By doing so, you can save other

readers from frustration and help us improve subsequent versions of this book. If you nd

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selecting your book, clicking on the errata submission form link, and entering the details

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will be uploaded on our website, or added to any list of existing errata, under the Errata

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Questions

You can contact us at questions@packtpub.com if you are having a problem with

any aspect of the book, and we will do our best to address it.

Thread Management

Another concept related to concurrency is parallelism. There are different denitions and

relations with the concurrency concept. Some authors talk about concurrency when you

execute your application with multiple threads in a single-core processor, so simultaneously

you can see when your program execution is apparent. Also, you can talk about parallelism

when you execute your application with multiple threads in a multi-core processor or in a

computer with more than one processor. Other authors talk about concurrency when the

threads of the application are executed without a predened order, and talk about parallelism

when you use various threads to simplify the solution of a problem, where all these threads

are executed in an ordered way.

This chapter presents a number of recipes that show how to perform basic operations with

threads using the Java 7 API. You will see how to create and run threads in a Java program,

how to control their execution, and how to group some threads to manipulate them as a unit.

Creating and running a thread

In this recipe, we will learn how to create and run a thread in a Java application. As with every

element in the Java language, threads are objects. We have two ways of creating a thread

in Java:

f Extending the Thread class and overriding the run() method

f Building a class that implements the Runnable interface and then creating

an object of the Thread class passing the Runnable object as a parameter

In this recipe, we will use the second approach to create a simple program that creates

and runs 10 threads. Each thread calculates and prints the multiplication table of a number

between one and 10.

Getting ready

The example of this recipe has been implemented using the Eclipse IDE. If you use Eclipse

or another IDE such as NetBeans, open it and create a new Java project.

How to do it...

Follow these steps to implement the example:

1. Create a class named Calculator that implements the Runnable interface.

public class Calculator implements Runnable {

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精通Java 7多线程开发：并行指南

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