Java使用Condition控制线程通信的方法实例详解

public class Account
{
   // 显式定义Lock对象
   private final Lock lock = new ReentrantLock();
   // 获得指定Lock对象对应的Condition
   private final Condition cOnd= lock.newCondition();
   // 封装账户编号、账户余额的两个成员变量
   private String accountNo;
   private double balance;
   // 标识账户中是否已有存款的旗标
   private boolean flag = false;
   public Account(){}
   // 构造器
   public Account(String accountNo , double balance)
   {
      this.accountNo = accountNo;
      this.balance = balance;
   }
   // accountNo的setter和getter方法
   public void setAccountNo(String accountNo)
   {
      this.accountNo = accountNo;
   }
   public String getAccountNo()
   {
      return this.accountNo;
   }
   // 因此账户余额不允许随便修改，所以只为balance提供getter方法，
   public double getBalance()
   {
      return this.balance;
   }
   public void draw(double drawAmount)
   {
      // 加锁
      lock.lock();
      try
      {
        // 如果flag为假，表明账户中还没有人存钱进去，取钱方法阻塞
        if (!flag)
        {
           cond.await();
        }
        else
        {
           // 执行取钱
           System.out.println(Thread.currentThread().getName()
              + " 取钱:" + drawAmount);
           balance -= drawAmount;
           System.out.println("账户余额为：" + balance);
           // 将标识账户是否已有存款的旗标设为false。
           flag = false;
           // 唤醒其他线程
           cond.signalAll();
        }
      }
      catch (InterruptedException ex)
      {
        ex.printStackTrace();
      }
      // 使用finally块来释放锁
      finally
      {
        lock.unlock();
      }
   }
   public void deposit(double depositAmount)
   {
      lock.lock();
      try
      {
        // 如果flag为真，表明账户中已有人存钱进去，则存钱方法阻塞
        if (flag)       // ①
        {
           cond.await();
        }
        else
        {
           // 执行存款
           System.out.println(Thread.currentThread().getName()
              + " 存款:" + depositAmount);
           balance += depositAmount;
           System.out.println("账户余额为：" + balance);
           // 将表示账户是否已有存款的旗标设为true
           flag = true;
           // 唤醒其他线程
           cond.signalAll();
        }
      }
      catch (InterruptedException ex)
      {
        ex.printStackTrace();
      }
      // 使用finally块来释放锁
      finally
      {
        lock.unlock();
      }
   }
   // 下面两个方法根据accountNo来重写hashCode()和equals()方法
   public int hashCode()
   {
      return accountNo.hashCode();
   }
   public boolean equals(Object obj)
   {
      if(this == obj)
        return true;
      if (obj !=null
        && obj.getClass() == Account.class)
      {
        Account target = (Account)obj;
        return target.getAccountNo().equals(accountNo);
      }
      return false;
   }
}

public class DrawThread extends Thread
{
   // 模拟用户账户
   private Account account;
   // 当前取钱线程所希望取的钱数
   private double drawAmount;
   public DrawThread(String name , Account account
      , double drawAmount)
   {
      super(name);
      this.account = account;
      this.drawAmount = drawAmount;
   }
   // 重复100次执行取钱操作
   public void run()
   {
      for (int i = 0 ; i <100 ; i++ )
      {
        account.draw(drawAmount);
      }
   }
}

public class DepositThread extends Thread
{
   // 模拟用户账户
   private Account account;
   // 当前取钱线程所希望存款的钱数
   private double depositAmount;
   public DepositThread(String name , Account account
      , double depositAmount)
   {
      super(name);
      this.account = account;
      this.depositAmount = depositAmount;
   }
   // 重复100次执行存款操作
   public void run()
   {
      for (int i = 0 ; i <100 ; i++ )
      {
        account.deposit(depositAmount);
      }
   }
}

public class DrawTest
{
   public static void main(String[] args)
   {
      // 创建一个账户
      Account acct = new Account("1234567" , 0);
      new DrawThread("取钱者" , acct , 800).start();
      new DepositThread("存款者甲" , acct , 800).start();
      new DepositThread("存款者乙" , acct , 800).start();
      new DepositThread("存款者丙" , acct , 800).start();
   }
}