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