java多线程面试题

1、有三个线程ID分别是A、B、C,请有多线编程实现，在屏幕上循环打印10次ABCABC…

由于线程执行的不确定性，要保证这样有序的输出，必须控制好多线程的同步。

线程同步有两种基本方法：

（1） synchronized

（2） wait,notify,notifyAll

现在分别采用这两种方法来解答这道题目。

注：此面试题主要考查，面试者线程并发的问题。可以参考：生产者-消费者模型。

方法1：使用 synhronized同步代码块

 1 class Method1 implements Runnable {
 2     private String name = "";
 3     private StartLock lock = null;
 4     private int count = 10;
 5 
 6     public Method1(String name, StartLock lock) {
 7         this.name = name;
 8         this.lock = lock;
 9 
10     }
11 
12     public void run() {
13         while (count > 0) {
14             synchronized (lock) {
15                 if (lock.getName().equalsIgnoreCase(this.name)) {
16                     System.out.print("当前线程名："
17                             + Thread.currentThread().getName() + " " + name
18                             + "    ");
19 
20                     if (name == "C") {
21                         System.out.println();
22                     }
23 
24                     count--;
25 
26                     if (this.name.equals("A")) {
27                         lock.setName("B");
28                     } else if (this.name.equals("B")) {
29                         lock.setName("C");
30                     } else if (this.name.equals("C")) {
31                         lock.setName("A");
32                     }
33                 }
34             }
35         }
36     }
37 }

方法2：使用 wait,notify,notifyAll

 1 class Method2 implements Runnable {
 2     private String name = "";
 3     private StartLock lock = null;
 4     private int count = 10;
 5     
 6     public Method2(String name, StartLock lock) {
 7         this.name = name;
 8         this.lock = lock;
 9     }
10 
11     public void run() {
12         while (count > 0) {
13             synchronized (lock) {
14                 while (!lock.getName().equalsIgnoreCase(this.name)) {
15                     try {
16                         lock.wait();
17                     } catch (InterruptedException e) {
18                         e.printStackTrace();
19                     }
20                 }
21 
22                 System.out.print(name);
23 
24                 count--;
25 
26                 if (this.name.equals("A")) {
27                     lock.setName("B");
28                 } else if (this.name.equals("B")) {
29                     lock.setName("C");
30                 } else if (this.name.equals("C")) {
31                     lock.setName("A");
32                 }
33                 lock.notifyAll();
34             }
35         }
36     }
37 }

测试：

 1 class StartLock {//锁对象
 2     public String name = "A";
 3     
 4     public String getName() {
 5         return name;
 6     }
 7     public void setName(String name) {
 8         this.name = name;
 9     }
10 }
11 
12 public class Test  {
13     public static void main(String[] args) {
14         StartLock lock = new StartLock();
15         
16         //new Thread(new Method1("A", lock)).start();
17         //new Thread(new Method1("B", lock)).start();
18         //new Thread(new Method1("C", lock)).start();
19         
20         new Thread(new Method2("A", lock)).start();
21         new Thread(new Method2("B", lock)).start();
22         new Thread(new Method2("C", lock)).start();
23     }
24 }