Java的线程基本用法

创建线程的方法：

实现Runnable接口

首先我们查看Runnable接口的定义：

package java.lang;
@FunctionalInterface
public interface Runnable {
    public abstract void run();
}

单纯通过代码，我们可以得到的信息有：

• 这个接口是一个函数式接口，所以有且只有一个抽象方法需要被实现；
• 实际上线程运行的代码块，都在run方法中；

关于Runnable接口更多详细的说明，我想没有什么是比官方文档更精确的了：

/**
 * The Runnable interface should be implemented by any
 * class whose instances are intended to be executed by a thread. The
 * class must define a method of no arguments called run.
 * <p>
 * This interface is designed to provide a common protocol for objects that
 * wish to execute code while they are active. For example,
 * Runnable is implemented by class Thread.
 * Being active simply means that a thread has been started and has not
 * yet been stopped.
 * <p>
 * In addition, Runnable provides the means for a class to be
 * active while not subclassing Thread. A class that implements
 * Runnable can run without subclassing Thread
 * by instantiating a Thread instance and passing itself in
 * as the target.  In most cases, the Runnable interface should
 * be used if you are only planning to override the run()
 * method and no other Thread methods.
 * This is important because classes should not be subclassed
 * unless the programmer intends on modifying or enhancing the fundamental
 * behavior of the class.
 *
 * @author  Arthur van Hoff
 * @see     java.lang.Thread
 * @see     java.util.concurrent.Callable
 * @since   JDK1.0
 */

翻译下：

• 任何想要其实例被放到线程里来执行的类都必须实现Runnable接口，这个类必须定义一个无参的run()方法。
• 这个接口设计出来是为对象提供一个公用的协议，当对象活跃时执行相应的代码。比如Thread类就实现了Runnable接口。活跃的意思是一个线程已经启动并且还没用被终止。
• 总的来讲，Runnable接口提供了一种方法，在不继承Thread类的情况下来创建一个线程运行需要的类。一个实现了Runnable接口的类可以把自身的实例作为参数传递给Thread类来创建线程运行，而不用继承Thread类。绝大多数情况下，如果你只是想重写run()方法中的代码而不想修改Thread类中其他的方法，那你应该使用Runnable接口。
• 这很重要，因为除非你想要修改或者增强一个类，否则原则上是不应该继承这个类的。

关于run方法的注释：

/**
 * When an object implementing interface Runnable is used
 * to create a thread, starting the thread causes the object's
 * run method to be called in that separately executing
 * thread.
 * <p>
 * The general contract of the method run is that it may
 * take any action whatsoever.
 *
 * @see     java.lang.Thread#run()
 */

翻译下：

当一个实现了Runnable接口的类被用来创建一个线程时，开始这个线程会在这个单独的线程里执行run方法里的代码。run方法设计的理念就是它可以用来干任何事。

看到这里应该说Runnable接口的设计理念和用途已经非常清晰了，简单来说，它就是定义了一个规范，规定任何需要创建线程执行的代码都应该实现runnable接口，并把代码放入到run方法中。当线程启动时，就会在这个线程中执行run方法中的代码。

下面写一个简单的示例来演示Runnable接口的使用：

package org.xtf2009.concurrent.runnable;

public class RunnableDemo implements Runnable {

    @Override
    public void run() {
        System.out.println("I am running in Thread:" + Thread.currentThread().getName());
    }

    public static void main(String[] args) {
        System.out.println("Start main in Thread:"+ Thread.currentThread().getName());
        Thread t = new Thread(new RunnableDemo());//创建一个Thread类，传入RunnableDemo的实例
        t.start();//线程启动后，就会执行run方法中的代码
        System.out.println("End main in Thread:"+ Thread.currentThread().getName());
    }
}

看下输出结果：

Start main in Thread:main
End main in Thread:main
I am running in Thread:Thread-0