线程-主线程等待子线程

在开发中多线程并发问题，数据安全，很重要，

如果用了多线程就不的不考虑数据安全，

如何让主线程等待所有子线程都执行完，在继续执行？

方法很多，

1.在主方法中做现场数标记，如果有子线程没执行完就循环检测。

2.Thread.join()方法等待线程结束。

第一种方法：

package com.yangtb.Thread;

import java.util.Random;

public class ThreadJoin {
    int intThreadNum;//记录子线程个数

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ThreadJoin tj = new ThreadJoin();
        tj.run();
        System.out.println("主线程结束");
    }



    class Work implements Runnable{
        String name;
        int sleeptime;
        Work(String name, int sleeptime){
            this.name = name;
            this.sleeptime=sleeptime;
        }
        public void run() {

            // TODO Auto-generated method stub
            try {
                               //线程加1
                upThread();
                Thread.sleep(sleeptime);
                System.out.println(name+"---end---sleep :"+sleeptime);

                downThread();//线程减1
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

    }



    public  void run(){

        int time = 10000;
        Random r = new Random();
        Thread[] rs = new Thread[10];
        for(int i =0;i<10;i++){

            rs[i] =new Thread(new Work(i+"",r.nextInt(time)));
            rs[i].start();
            System.out.println(i+"--Start---");
        }


        //每隔1秒检查是否还有线程，如果有就等1秒在检查，如果没有就结束
        while(isok()){
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

        System.out.println("----end--");
    }
    //线程结束
    private synchronized void downThread(){
        intThreadNum--;
    }
    //线程开始
    private synchronized void upThread(){
        intThreadNum++;
    }
    //检查现场数
    private synchronized boolean isok(){
        return intThreadNum>0;
    }

}

 

第二种方法：Thread.join();

package com.yangtb.Thread;

import java.util.Random;

public class ThreadJoin {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ThreadJoin tj = new ThreadJoin();
        tj.run();
        System.out.println("主线程结束");
    }



    class Work implements Runnable{
        String name;
        int sleeptime;
        Work(String name, int sleeptime){
            this.name = name;
            this.sleeptime=sleeptime;
        }
        public void run() {

            // TODO Auto-generated method stub
            try {

                Thread.sleep(sleeptime);
                System.out.println(name+"---end---sleep :"+sleeptime);

            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

    }



    public  void run(){

        int time = 10000;
        Random r = new Random();
        Thread[] rs = new Thread[10];
        for(int i =0;i<10;i++){

            rs[i] =new Thread(new Work(i+"",r.nextInt(time)));
            rs[i].start();
            System.out.println(i+"--Start---");
        }

        for(Thread rtemp : rs){
            try {
                rtemp.join();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        for(Thread rtemp : rs){
            try {
                rtemp.join();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

        System.out.println("----end--");
    }



}