java for循环改造多线程例子

package com.company;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Main {

    public static void main(String[] args) {
        // write your code here
        System.out.println("Hello World");
        int TOTAL_THREADS = 4;//线程数
        //数据库中的100条数据;
        List list = new ArrayList();
        for (int i = 0; i < 100; i++) {
            list.add(i);
        }
        //Executors创建线程池new固定的10个线程
        ExecutorService taskExecutor = Executors.newCachedThreadPool();
        final CountDownLatch latch = new CountDownLatch(list.size());//用于判断所有的线程是否结束
        System.out.println("个数==" + list.size());

        for (int m = 0; m < list.size(); m++) {
            final int n = m;//内部类里m不能直接用,所以赋值给n
            Runnable run = new Runnable() {
                public void run() {
                    try {
                        System.out.println("我在执行=" + n);
                    } finally {
                        latch.countDown(); //每次调用CountDown()，计数减1
                    }
                }
            };
            taskExecutor.execute(run);//开启线程执行池中的任务。还有一个方法submit也可以做到，它的功能是提交指定的任务去执行并且返回Future对象，即执行的结果
        }

        try {
            //等待所有线程执行完毕
            latch.await();//主程序执行到await()函数会阻塞等待线程的执行，直到计数为0
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        taskExecutor.shutdown();//关闭线程池
        //所有线程执行完毕,执行主线程
    }

}