多线程概述

线程的创建和启动

1.1 继承 Thread 类创建线程

步骤如下:

• 定义 Thread 的子类,并重写该类的 run() 方法.该方法表示线程需要完成的任务,因此 run() 方法被称为线程执行体
• 创建 Thread 子类的实例,即创建了线程对象
• 调用线程对象的 start() 方法启动该线程

FirstThread.java(继承 Thread 的子类)

package Threads;/*
 * @Author Sheng WenZeng
 * @Date 2019/9/7 17:51
 * @Version 1.0
 */

/**
 * @author Sheng Wenzeng
 * @ClassName FirstThread
 * @Description TODO
 * @Date 2019/9/7 17:51
 * @Version 1.0
 */
public class FirstThread extends Thread {
    private int i;

    public static void main(String[] args) {
        for (int i = 0; i < 100; i++) {
            System.out.println(Thread.currentThread().getName() + "  " + i);
            if (i == 20) {
                new FirstThread().start();
                new FirstThread().start();
                System.out.println(Thread.currentThread().getName() + "  " + i);
            }
        }
    }

    @Override
    public void run() {
        for (; i < 100; i++) {
            // 当线程类继承 Thread 时,直接使用 this 可以获取当前线程
            // Thread 对象的 getName() 方法可以获得当前线程的名字
            System.out.println(this.getName() + "  " + i);
        }
    }
}

运行结果:

............
main  74
main  75
main  76
main  77
main  78
main  79
main  80
main  81
main  82
main  83
main  84
main  85
main  86
main  87
main  88
main  89
main  90
main  91
main  92
main  93
main  94
main  95
main  96
main  97
main  98
main  99
Thread-0  0
Thread-0  1
Thread-0  2
Thread-0  3
Thread-0  4
Thread-0  5
Thread-0  6
Thread-0  7
Thread-0  8
Thread-0  9
Thread-0  10
Thread-0  11
Thread-0  12
Thread-0  13
Thread-0  14
Thread-0  15
Thread-0  16
Thread-0  17
Thread-0  18
Thread-0  19
Thread-0  20
Thread-0  21
Thread-0  22
Thread-0  23
Thread-1  0
Thread-0  24
Thread-1  1
Thread-0  25
Thread-0  26
Thread-0  27
Thread-0  28
Thread-0  29
Thread-0  30
Thread-0  31
Thread-0  32
Thread-0  33
Thread-0  34
Thread-0  35
Thread-0  36
Thread-0  37
Thread-0  38
Thread-0  39
Thread-0  40
Thread-0  41
Thread-0  42
Thread-0  43
Thread-0  44
Thread-0  45
Thread-0  46
Thread-0  47
Thread-0  48
Thread-0  49
Thread-0  50
Thread-0  51
Thread-0  52
Thread-0  53
Thread-0  54
Thread-0  55
Thread-0  56
Thread-0  57
Thread-0  58
Thread-0  59
Thread-0  60
Thread-0  61
Thread-0  62
Thread-0  63
Thread-0  64
Thread-0  65
Thread-0  66
Thread-1  2
Thread-1  3
Thread-1  4
Thread-1  5
Thread-1  6
Thread-1  7
Thread-1  8
Thread-1  9
Thread-1  10
Thread-1  11
.........

Main类中的main方法就是一个线程,然后调用了另外两个线程,这两个线程的实例不能共享

1.2 实现 Runable 接口创建线程类

SecondThread.java(实现 Runable接口)

package Threads;/*
 * @Author Sheng WenZeng
 * @Date 2019/9/7 18:09
 * @Version 1.0
 */

/**
 * @author Sheng Wenzeng
 * @ClassName SecondThread
 * @Description TODO
 * @Date 2019/9/7 18:09
 * @Version 1.0
 */
public class SecondThread implements Runnable {

    @Override
    public void run() {
        int i = 0;
        for (; i < 100; i++) {
            System.out.println(Thread.currentThread().getName() + "  " + i);
        }
    }
}

Main.java

package Threads;/*
 * @Author Sheng WenZeng
 * @Date 2019/9/7 18:09
 * @Version 1.0
 */

/**
 * @author Sheng Wenzeng
 * @ClassName SecondThread
 * @Description TODO
 * @Date 2019/9/7 18:09
 * @Version 1.0
 */
public class SecondThread implements Runnable {
    private int i;

    public static void main(String[] args) {
        for (int i = 0; i < 200; i++) {
            System.out.println(Thread.currentThread().getName() + "  " + i);
            if (i == 20) {
                SecondThread st = new SecondThread();
                new Thread(st, "线程一").start();
                new Thread(st, "线程二").start();
            }
        }
    }

    @Override
    public void run() {
        for (; i < 200; i++) {
            System.out.println(Thread.currentThread().getName() + "  " + i);
        }
    }
}

运行结果:

main  0
main  1
main  2
main  3
main  4
main  5
main  6
main  7
main  8
main  9
main  10
main  11
main  12
main  13
main  14
main  15
main  16


.......................


线程一  38
线程一  39
线程一  40
线程一  41
线程一  42
线程一  43
线程一  44
线程一  45
线程一  46
线程一  47
线程一  48
线程一  49
线程一  50
线程一  51
线程一  52
线程一  53
线程一  54
线程一  55
线程二  55
线程二  56
线程二  57
线程二  58
线程二  59
线程二  60
线程二  61
线程二  62
线程二  63
线程二  64
线程二  65
线程二  66
..............

使用 Runable 接口的线程之间可以共享实例变量