Java 使用 Thread 类代表线程，所有的线程对象都必须是 Thread 类或其子类的实例。每个线程的作用是完成一定的任务，实际上就是执行一段程序流（一段顺序执行的代码）。 Java 使用线程执行体来代表这段程序流。
继承 Thread 类创建线程类
通过继承 Thread 类来创建并启动多线程的步骤如下。
- 定义 Thread 类的子类，并重写该类的 run() 方法，该 run() 方法的方法体就代表了线程需要完成的任务。因此把 run() 方法称为线程执行体。
- 创建 Thread 子类的实例，即创建了线程对象。
- 调用线程对象的 start() 方法来启动该线程。
下面程序示范了通过继承 Thread 类来创建并启动多线程。
//通过继承Thread类来创建线程类 public class FirstThread extends Thread { private int i = 0; // 重写run()方法的方法体就是线程执行体 public void run() { for (; i < 100; i++) { // 当线程类继承Thread时，直接使用this即可获取当前线程 // Thread对象的getName()方法返回当前线程的名字 // 因此可以直接调用getName()方法返回当前线程的名字 System.out.println(getName() + " " + i); } } public static void main(String[] args) { for (int i = 0; i < 100; i++) { // 调用Thread的currentThread()方法获取当前线程 System.out.println(Thread.currentThread().getName() + " " + i); if (i == 20) { // 创建并启动第一个线程 new FirstThread().start(); // 创建并启动第二个线程 new FirstThread().start(); } } } }
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