Java中join的使用

package com.jack.test;

public class TestJoin implements Runnable{
    public static int a = 0;
    
    public void run(){
        try{
            Thread.sleep(1100);
            for(int i = 0; i < 5; i++){
                a = a +1;
            }
            System.out.println("after for loop, a="+a);
        }catch(InterruptedException e){
            e.printStackTrace();
        }
        
    }
    
    public static void main(String[] args) throws InterruptedException{
        Runnable r = new TestJoin();
        Thread t = new Thread(r);
        t.start();
        t.join();
        System.out.println(a);
    }

}