java 多个线程按顺序打印字符 

 1 public class ABCTest {
 2 
 3     private final static Object lock = new Object();
 4     private static int COUNT = 1;
 5     private static int NUM = 4;
 6     public static void main(String[] args) throws InterruptedException {
 7         MyPrint a = new MyPrint(1);
 8         MyPrint b = new MyPrint(2);
 9         MyPrint c = new MyPrint(3);
10         MyPrint d = new MyPrint(4);
11         a.start();
12         b.start();
13         c.start();
14         d.start();
15         a.join();
16         b.join();
17         c.join();
18         d.join();
19 
20     }
21 
22     private static class MyPrint extends Thread {
23 
24         private int name;
25 
26         public MyPrint(int name) {
27             this.name = name;
28         }
29 
30         @Override
31         public void run() {
32             for (int i = 0; i < 10; i++) {
33                 for (int j = 1; j <= NUM; j ++) {
34                     if (j == name) {
35                         waitAndPrint();
36                     }
37                 }
38 
39             }
40         }
41 
42         private void waitAndPrint() {
43             while (true) {
44                 synchronized (lock) {
45                     if (COUNT == name) {
46                        // System.out.println("count = " + COUNT);
47                         print();
48                         COUNT = name % NUM + 1;
49                         lock.notifyAll();
50                         break;
51                     } else {
52                         try {
53                             lock.wait();
54                         } catch (InterruptedException e) {
55                             e.printStackTrace();
56                         }
57                     }
58                 }
59             }
60         }
61 
62         private void print() {
63             System.out.println((char)(name + 64));
64         }
65     }
66 }

常见的java多线程面试题，是更好的理解wait notify ,本质是生产者消费者模型。

要思考wait 的时候为什么要用while,而不是if (因为如果用if 方法结束后这个线程就结束了，不能被 block 住)

 

posted on 2018-08-30 17:58  cococooder  阅读(408)  评论(0)    收藏  举报