Java知多少（63）线程间通信

 1 // An incorrect implementation of a producer and consumer.
 2 class Q {
 3     int n;
 4     synchronized int get() {
 5         System.out.println("Got: " + n);
 6         return n;
 7     }
 8     synchronized void put(int n) {
 9         this.n = n;
10         System.out.println("Put: " + n);
11     }
12 }
13 class Producer implements Runnable {
14     Q q;
15     Producer(Q q) {
16         this.q = q;
17         new Thread(this, "Producer").start();
18     }
19     public void run() {
20         int i = 0;
21         while(true) {
22             q.put(i++);
23         }
24     }
25 }
26 class Consumer implements Runnable {
27     Q q;
28     Consumer(Q q) {
29         this.q = q;
30         new Thread(this, "Consumer").start();
31     }
32     public void run() {
33         while(true) {
34            q.get();
35         }
36     }
37 }
38 class PC {
39     public static void main(String args[]) {
40         Q q = new Q();
41         new Producer(q);
42         new Consumer(q);
43         System.out.println("Press Control-C to stop.");
44     }
45 }

 1 // A correct implementation of a producer and consumer.
 2 class Q {
 3     int n;
 4     boolean valueSet = false;
 5     synchronized int get() {
 6         if(!valueSet)
 7             try {
 8                 wait();
 9             } catch(InterruptedException e) {
10                 System.out.println("InterruptedException caught");
11             }
12             System.out.println("Got: " + n);
13             valueSet = false;
14             notify();
15             return n;
16         }
17         synchronized void put(int n) {
18             if(valueSet)
19             try {
20                 wait();
21             } catch(InterruptedException e) {
22                 System.out.println("InterruptedException caught");
23             }
24             this.n = n;
25             valueSet = true;
26             System.out.println("Put: " + n);
27             notify();
28         }
29     }
30     class Producer implements Runnable {
31         Q q;
32         Producer(Q q) {
33         this.q = q;
34         new Thread(this, "Producer").start();
35     }
36     public void run() {
37         int i = 0;
38         while(true) {
39             q.put(i++);
40         }
41     }
42 }
43 class Consumer implements Runnable {
44     Q q;
45     Consumer(Q q) {
46         this.q = q;
47         new Thread(this, "Consumer").start();
48     }
49     public void run() {
50         while(true) {
51             q.get();
52         }
53     }
54 }
55 class PCFixed {
56     public static void main(String args[]) {
57         Q q = new Q();
58         new Producer(q);
59         new Consumer(q);
60         System.out.println("Press Control-C to stop.");
61     }
62 }