在真实开发 中关于多线程的通讯的问题用到下边的例子是比较多的
不同的地方时if 和while 的区别 如果只是两个线程之间的通讯，使用if是没有问题的。
但是在多个线程之间就会有问题
1 /* 2 * 这个例子用来解释多个生产者和多个消费者的情况 3 */ 4 5 /* 6 * 资源库 7 */ 8 class Resource 9 { 10 private String name; 11 private int count = 1; 12 private boolean flag = false; 13 public synchronized void set (String name){ 14 15 while (flag) 16 try {this.wait();} 17 catch(Exception e){ 18 19 } 20 this .name = name + "--" + count++; 21 System.out.println(Thread.currentThread().getName()+"生产商品"+this.name); 22 flag = true; 23 this.notifyAll(); 24 25 } 26 27 28 public synchronized void out(){ 29 while (!flag) 30 try {this.wait();} 31 catch(Exception e){ 32 33 } 34 System.out.println(Thread.currentThread().getName() + "消费了" + this.name); 35 flag = false; 36 this.notifyAll(); 37 } 38 39 } 40 41 /* 42 * 生产者 43 */ 44 class Producer implements Runnable 45 { 46 private Resource res; 47 Producer (Resource res){ 48 49 this.res = res; 50 } 51 public void run(){ 52 53 while (true){ 54 55 res.set ("牙膏"); 56 } 57 } 58 59 60 } 61 /* 62 * 消费者 63 */ 64 class Consumer implements Runnable 65 { 66 67 private Resource res; 68 Consumer(Resource res){ 69 70 this.res = res; 71 } 72 public void run(){ 73 74 while (true){ 75 res.out(); 76 } 77 } 78 } 79 public class producerConsumerDemo { 80 81 public static void main(String[] args) { 82 // TODO Auto-generated method stub 83 Resource res = new Resource(); 84 85 Producer p1 = new Producer(res); 86 Producer p2 = new Producer(res); 87 88 Consumer c1 = new Consumer(res); 89 Consumer c2 = new Consumer(res); 90 91 Thread t1 = new Thread(p1); 92 Thread t2 = new Thread(p2); 93 Thread t3 = new Thread(c1); 94 Thread t4 = new Thread(c2); 95 96 t1.start(); 97 t2.start(); 98 t3.start(); 99 t4.start(); 100 101 102 103 } 104 105 }