java常見併發面試題目+示例代碼

一、如今有線程 T一、T2 和 T3。你如何確保 T2 線程在 T1 以後執行，而且 T3 線程在 T2 以後執行？

這個線程面試題一般在第一輪面試或電話面試時被問到，這道多線程問題爲了測試面試者是否熟悉join方法的概念。答案也很是簡單——能夠用 Thread 類的join方法實現這一效果。

 1 public class Test {  2 
 3     public static void main(String[] args) throws InterruptedException {  4         Thread t1 = new Thread() {  5             public void run() {  6                 System.out.println("1");  7  }  8  };  9         Thread t2 = new Thread() { 10             public void run() { 11                 System.out.println("2"); 12  } 13  }; 14         Thread t3 = new Thread() { 15             public void run() { 16                 System.out.println("3"); 17  } 18  }; 19         
20  t1.start(); 21         t1.join();//阻塞住直到t1完成
22  t2.start(); 23  t2.join(); 24  t3.start(); 25         System.out.println("end"); 26  } 27 }

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 二、兩線程奇偶數打印

 1 public class Test {  2     static class SoulutionTask implements Runnable {  3         static int value = 0;  4 
 5  @Override  6         public void run() {  7             while (value <= 100) {  8                 synchronized (SoulutionTask.class) {  9                     System.out.println(Thread.currentThread().getName() + ":" + value++); 10                     SoulutionTask.class.notify(); 11                     try { 12                         SoulutionTask.class.wait(); 13                     } catch (InterruptedException e) { 14  e.printStackTrace(); 15  } 16  } 17  } 18  } 19  } 20 
21     public static void main(String[] args) throws InterruptedException { 22         new Thread(new SoulutionTask(), "偶數").start(); 23         new Thread(new SoulutionTask(), "奇數").start(); 24  } 25 }

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N個線程循環打印

 1 public class Test implements Runnable {  2     private static final Object LOCK = new Object();  3     /**
 4  * 當前即將打印的數字  5      */
 6     private static int current = 0;  7     /**
 8  * 當前線程編號，從0開始  9      */
10     private int threadNo; 11     /**
12  * 線程數量 13      */
14     private int threadCount; 15     /**
16  * 打印的最大數值 17      */
18     private int maxInt; 19 
20     public Test(int threadNo, int threadCount, int maxInt) { 21         this.threadNo = threadNo; 22         this.threadCount = threadCount; 23         this.maxInt = maxInt; 24  } 25 
26  @Override 27     public void run() { 28         while (true) { 29             synchronized (LOCK) { 30                 // 判斷是否輪到當前線程執行
31                 while (current % threadCount != threadNo) { 32                     if (current > maxInt) { 33                         break; 34  } 35                     try { 36                         // 若是不是，則當前線程進入wait
37  LOCK.wait(); 38                     } catch (Exception e) { 39  e.printStackTrace(); 40  } 41  } 42                 // 最大值跳出循環
43                 if (current > maxInt) { 44                     break; 45  } 46                 System.out.println("thread" + threadNo + " : " + current); 47                 current++; 48                 // 喚醒其餘wait線程
49  LOCK.notifyAll(); 50  } 51  } 52  } 53 
54     public static void main(String[] args) { 55         int threadCount = 3; 56         int max = 100; 57         for (int i = 0; i < threadCount; i++) { 58             new Thread(new Test(i, threadCount, max)).start(); 59  } 60  } 61 }

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