Java多线程通信之两个线程分别打印AB各10次

Posted 2020-06-21

一道经典的面试题目：两个线程，分别打印AB，其中线程A打印A，线程B打印B，各打印10次，使之出现ABABABABA.. 的效果

 1 package com.shangshe.path;
 2 
 3 public class ThreadAB {
 4 
 5     /**
 6      * @param args
 7      */
 8     public static void main(String[] args) {
 9         
10         final Print business = new Print();
11         
12         new Thread(new Runnable() {
13             public void run() {
14                 for(int i=0;i<10;i++) {
15                     business.print_A();
16                 }
17             }
18         }).start();
19         
20         new Thread(new Runnable() {
21             public void run() {
22                 for(int i=0;i<10;i++) {
23                     business.print_B();
24                 }
25             }
26         }).start();
27         
28     }
29 }
30 class Print {
31     
32     private boolean flag = true;
33     
34     public synchronized void print_A () {
35         while(!flag) {
36             try {
37                 this.wait();
38             } catch (InterruptedException e) {
39                 // TODO Auto-generated catch block
40                 e.printStackTrace();
41             }
42         }
43         System.out.print("A");
44         flag = false;
45         this.notify();
46     }
47     
48     public synchronized void print_B () {
49         while(flag) {
50             try {
51                 this.wait();
52             } catch (InterruptedException e) {
53                 // TODO Auto-generated catch block
54                 e.printStackTrace();
55             }
56         }
57         System.out.print("B");
58         flag = true;
59         this.notify();
60     }
61 }

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由上面的例子我们可以设计出3个线程乃至于n个线程的程序，下面给出的例子是3个线程，分别打印A，B，C 10次，使之出现ABCABC.. 的效果

 

 1 public class ThreadABC {
 2 
 3     /**
 4      * @param args
 5      */
 6     public static void main(String[] args) {
 7         
 8         final Print business = new Print();
 9         
10         new Thread(new Runnable() {
11             public void run() {
12                 for(int i=0;i<100;i++) {
13                     business.print_A();
14                 }
15             }
16         }).start();
17         
18         new Thread(new Runnable() {
19             public void run() {
20                 for(int i=0;i<100;i++) {
21                     business.print_B();
22                 }
23             }
24         }).start();
25         
26         new Thread(new Runnable() {
27             public void run() {
28                 for(int i=0;i<100;i++) {
29                     business.print_C();
30                 }
31             }
32         }).start();
33         
34     }
35 }
36 class Print {
37     
38     private boolean should_a = true;
39     private boolean should_b = false;
40     private boolean should_c = false;
41     
42     public synchronized void print_A () {
43         while(should_b || should_c) {
44             try {
45                 this.wait();
46             } catch (InterruptedException e) {
47                 // TODO Auto-generated catch block
48                 e.printStackTrace();
49             }
50         }
51         System.out.print("A");
52         should_a = false;
53         should_b = true;
54         should_c = false;
55         this.notifyAll();
56     }
57     
58     public synchronized void print_B () {
59         while(should_a || should_c) {
60             try {
61                 this.wait();
62             } catch (InterruptedException e) {
63                 // TODO Auto-generated catch block
64                 e.printStackTrace();
65             }
66         }
67         System.out.print("B");
68         should_a = false;
69         should_b = false;
70         should_c = true;
71         this.notifyAll();
72     }
73     
74     public synchronized void print_C () {
75         while(should_a || should_b) {
76             try {
77                 this.wait();
78             } catch (InterruptedException e) {
79                 // TODO Auto-generated catch block
80                 e.printStackTrace();
81             }
82         }
83         System.out.print("C");
84         should_a = true;
85         should_b = false;
86         should_c = false;
87         this.notifyAll();
88     }
89 }

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再一次证明了软件工程的重要性了；在多线程程序中，应该说在程序中，我们应该把那些业务逻辑代码放到同一个类中，使之高内聚，低耦合