Java多线程实现同时输出

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

 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

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