java使用condition進行線程通信

package cond;

import java.util.concurrent.*;
import java.util.concurrent.locks.*;
 
public class Account
{
	// 顯式定義Lock對象
	private final Lock lock = new ReentrantLock();
	// 獲得指定Lock對象對應的Condition
	private final Condition cond  = lock.newCondition();
	// 封裝賬戶編號、賬戶餘額的兩個成員變量
	private String accountNo;
	private double balance;
	// 標識賬戶中是否已有存款的旗標
	private boolean flag = false;

	public Account(){}
	// 構造器
	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;
	}
	// 因此賬戶餘額不允許隨便修改，所以只爲balance提供getter方法，
	public double getBalance()
	{
		return this.balance;
	}

	public void draw(double drawAmount)
	{
		// 加鎖
		lock.lock();
		try
		{
			// 如果flag爲假，表明賬戶中還沒有人存錢進去，取錢方法阻塞
			if (!flag)
			{
				cond.await();
			}
			else
			{
				// 執行取錢
				System.out.println(Thread.currentThread().getName()
					+ " 取錢:" +  drawAmount);
				balance -= drawAmount;
				System.out.println("賬戶餘額爲：" + balance);
				// 將標識賬戶是否已有存款的旗標設爲false。
				flag = false;
				// 喚醒其他線程
				cond.signalAll();
			}
		}
		catch (InterruptedException ex)
		{
			ex.printStackTrace();
		}
		// 使用finally塊來釋放鎖
		finally
		{
			lock.unlock();
		}
	}
	public void deposit(double depositAmount)
	{
		lock.lock();
		try
		{
			// 如果flag爲真，表明賬戶中已有人存錢進去，則存錢方法阻塞
			if (flag)             // ①
			{
				cond.await();
			}
			else
			{
				// 執行存款
				System.out.println(Thread.currentThread().getName()
					+ " 存款:" +  depositAmount);
				balance += depositAmount;
				System.out.println("賬戶餘額爲：" + balance);
				// 將表示賬戶是否已有存款的旗標設爲true
				flag = true;
				// 喚醒其他線程
				cond.signalAll();
			}
		}
		catch (InterruptedException ex)
		{
			ex.printStackTrace();
		}
		// 使用finally塊來釋放鎖
		finally
		{
			lock.unlock();
		}
	}

	// 下面兩個方法根據accountNo來重寫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;
	}
}

package cond;


 
public class DepositThread extends Thread
{
	// 模擬用戶賬戶
	private Account account;
	// 當前取錢線程所希望存款的錢數
	private double depositAmount;
	public DepositThread(String name , Account account
		, double depositAmount)
	{
		super(name);
		this.account = account;
		this.depositAmount = depositAmount;
	}
	// 重複100次執行存款操作
	public void run()
	{
		for (int i = 0 ; i < 100 ; i++ )
		{
			account.deposit(depositAmount);
		}
	}
}

package cond;


 
public class DrawThread extends Thread
{
	// 模擬用戶賬戶
	private Account account;
	// 當前取錢線程所希望取的錢數
	private double drawAmount;
	public DrawThread(String name , Account account
		, double drawAmount)
	{
		super(name);
		this.account = account;
		this.drawAmount = drawAmount;
	}
	// 重複100次執行取錢操作
	public void run()
	{
		for (int i = 0 ; i < 100 ; i++ )
		{
			account.draw(drawAmount);
		}
	}
}

package cond;


 
public class DrawTest
{
	public static void main(String[] args)
	{
		// 創建一個賬戶
		Account acct = new Account("1234567" , 0);
		new DrawThread("取錢者" , 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();
	}
}

賬戶餘額爲：0.0
存款者乙 存款:800.0
賬戶餘額爲：800.0
取錢者 取錢:800.0
賬戶餘額爲：0.0
存款者乙 存款:800.0
賬戶餘額爲：800.0
取錢者 取錢:800.0
賬戶餘額爲：0.0
存款者乙 存款:800.0
賬戶餘額爲：800.0