Java学习-068-多线程01：继承 Thread 类

进程是程序的一次动态执行过程，是程序代码加载 -> 代码执行 -> 执行完成的过程，此过程也是进程本身从产生，发展到最终消亡的过程。目前我们的操作系统均是多进程操作系统，能同时运行多个进程（程序），由于 CPU 具备分时机制，所以每个进程都能循环获得自己的 CPU 时间片，而且 CPU 执行速度非常快，使得所有程序好像是在同时运行一样。

多线程是实现并发机制的一种有效手段。进程和线程一样，都是实现并发的基本单位。线程是比进程更小的执行单位，是在进程的基础上更进一步的划分。所谓多线程是指一个进程在执行过程中产生的多个更小的程序单元，这些更小的单元称为线程，这些线程可以同时存在，同时运行，一个进程可能包含多个同时执行的线程。

Java程序每次运行时，至少启动两个线程，一个是mian线程，另一个是垃圾收集线程（Java本身具备垃圾回收的机制）。

Java可通过继承 Thread 类或实现 Runnable 接口来实现多线程。本文以集成 Thread 类为例实现多线程。代码如下所示：

package com.fanfengping.demo;

import lombok.extern.slf4j.Slf4j;

/**
 * Java程序里面对于继承永远都是存在有单继承局限的
 */
@Slf4j
public class ThreadDemo extends Thread{
    private Thread t;
    // 线程名称
    private String threadName;

    ThreadDemo(String tName) {
        threadName = tName;
        log.info("Create a thread : {}", threadName);
    }

    // 重写 run 方法，作为线程操作主体
    public void run() {
        log.info("Running Runnable Thread : {}", threadName);

        try {
            for(int i = 3; i > 0; i--) {
                log.info("Current Thread name is {}, work batch : {}", threadName, i);
                Thread.sleep(500);
            }
        } catch (InterruptedException e) {
            log.info("Thread {} interrupted!", threadName);
            e.printStackTrace();
        }

        log.info("Thread {} exit", threadName);
    }

    public void start() {
        log.info("Start Thread : {}", threadName);
        if (t == null) {
            t = new Thread(this, threadName);
            t.start();
        }
    }
}

  

编写测试类，代码如下所示：

package com.fanfengping.demo;

public class ThreadDemoTest {
    public static void main(String args[]) {
        ThreadDemo t1 = new ThreadDemo("ThreadDemo-1");
        t1.start();
        ThreadDemo t2 = new ThreadDemo("ThreadDemo-2");
        t2.start();
        ThreadDemo t3 = new ThreadDemo("ThreadDemo-3");
        t3.start();
        ThreadDemo t4 = new ThreadDemo("ThreadDemo-4");
        t4.start();
        ThreadDemo t5 = new ThreadDemo("ThreadDemo-5");
        t5.start();
    }
}

  

控制台输出如下所示：

[main] INFO com.fanfengping.demo.ThreadDemo - Create a thread : ThreadDemo-1
[main] INFO com.fanfengping.demo.ThreadDemo - Start Thread : ThreadDemo-1
[main] INFO com.fanfengping.demo.ThreadDemo - Create a thread : ThreadDemo-2
[main] INFO com.fanfengping.demo.ThreadDemo - Start Thread : ThreadDemo-2
[ThreadDemo-1] INFO com.fanfengping.demo.ThreadDemo - Running Runnable Thread : ThreadDemo-1
[main] INFO com.fanfengping.demo.ThreadDemo - Create a thread : ThreadDemo-3
[main] INFO com.fanfengping.demo.ThreadDemo - Start Thread : ThreadDemo-3
[ThreadDemo-1] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-1, work batch : 3
[ThreadDemo-2] INFO com.fanfengping.demo.ThreadDemo - Running Runnable Thread : ThreadDemo-2
[ThreadDemo-2] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-2, work batch : 3
[main] INFO com.fanfengping.demo.ThreadDemo - Create a thread : ThreadDemo-4
[main] INFO com.fanfengping.demo.ThreadDemo - Start Thread : ThreadDemo-4
[ThreadDemo-3] INFO com.fanfengping.demo.ThreadDemo - Running Runnable Thread : ThreadDemo-3
[main] INFO com.fanfengping.demo.ThreadDemo - Create a thread : ThreadDemo-5
[ThreadDemo-3] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-3, work batch : 3
[main] INFO com.fanfengping.demo.ThreadDemo - Start Thread : ThreadDemo-5
[ThreadDemo-4] INFO com.fanfengping.demo.ThreadDemo - Running Runnable Thread : ThreadDemo-4
[ThreadDemo-4] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-4, work batch : 3
[ThreadDemo-5] INFO com.fanfengping.demo.ThreadDemo - Running Runnable Thread : ThreadDemo-5
[ThreadDemo-5] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-5, work batch : 3
[ThreadDemo-1] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-1, work batch : 2
[ThreadDemo-4] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-4, work batch : 2
[ThreadDemo-3] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-3, work batch : 2
[ThreadDemo-2] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-2, work batch : 2
[ThreadDemo-5] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-5, work batch : 2
[ThreadDemo-1] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-1, work batch : 1
[ThreadDemo-3] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-3, work batch : 1
[ThreadDemo-4] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-4, work batch : 1
[ThreadDemo-5] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-5, work batch : 1
[ThreadDemo-2] INFO com.fanfengping.demo.ThreadDemo - Current Thread name is ThreadDemo-2, work batch : 1
[ThreadDemo-4] INFO com.fanfengping.demo.ThreadDemo - Thread ThreadDemo-4 exit
[ThreadDemo-1] INFO com.fanfengping.demo.ThreadDemo - Thread ThreadDemo-1 exit
[ThreadDemo-5] INFO com.fanfengping.demo.ThreadDemo - Thread ThreadDemo-5 exit
[ThreadDemo-2] INFO com.fanfengping.demo.ThreadDemo - Thread ThreadDemo-2 exit
[ThreadDemo-3] INFO com.fanfengping.demo.ThreadDemo - Thread ThreadDemo-3 exit

  

从上述程序运行输出日志可以看出，多个线程对象是交错运行的。线程是否运行，取决于线程对象是否被分配并获得了 CPU 资源。所以程序每次的运行结果通常是不一样的。另外，线程启动时虽然调用的是 start() 方法，实际上最终调用的却是 run() 方法定义的主体。

线程命名方式有如下两种：

1. 系统默认生成：new Thread(ThreadDemo)
2. 指定线程名称：new Thread(ThreadDemo, "线程名称")