java线程学习6——线程同步之同步锁-优快云博客

本文通过Java代码实现了一个带有同步机制的账户类(Account)，并利用ReentrantLock来保证线程安全。通过创建多个线程尝试从同一个账户中取款，演示了如何避免并发修改异常。

import java.util.concurrent.locks.ReentrantLock;

public class Account
{
/**
* 同步锁
*/
private final ReentrantLock lock = new ReentrantLock();

/**
* 账户号
*/
private String accountNo;
/**
* 账户余额
*/
private double balance;

public Account()
{
super();
}

public Account(String accountNo, double balance)
{
  super();
  this.accountNo = accountNo;
  this.balance = balance;
}

@Override
public int hashCode()
{
return accountNo.hashCode();
}

@Override
public boolean equals(Object obj)
{
  if (null != obj && obj.getClass() == Account.class)
  {
   Account target = (Account) obj;
   return target.accountNo.equals(accountNo);
  }
  return false;
}

/**
* 同步方法，同步方法的监视器是this，同步方法可以将该类变为线程安全的类
* 任何时候只有一个线程获得对Account对象的锁定，然后进入draw方法进行取钱
*/
public void draw(double drawAmount)
{
  lock.lock();
  try
  {
   if (balance >= drawAmount)
   {
    System.out.println(Thread.currentThread().getName()

          + "取出钞票成功" + drawAmount);
    balance -= drawAmount;
    System.out.println("余额为" + balance);
   }
   else
   {
    System.out.println("余额不足");
   }
  }
  finally
  {
   // 用finally块保证释放锁
   lock.unlock();
  }
}

/* 只提供Getters，不提供Setters，确保安全*/

public String getAccountNo()
{
return accountNo;
}

public double getBalance()
{
return balance;
}
}

public class DrawThread extends Thread
{
/**
* 模拟账户
*/
private Account ac;

/**
* 当前取钱线程希望取得的钱数
*/
private double drawAmount;

public DrawThread(String name, Account ac, double drawAmount)
{
  super(name);
  this.ac = ac;
  this.drawAmount = drawAmount;
}

@Override
public void run()
{
ac.draw(drawAmount);
}
}

public class Test
{
public static void main(String[] args)
{
  Account ac = new Account("00000001", 1000);
  Thread t1 = new Thread(new DrawThread("Lily", ac, 800));
  Thread t2 = new Thread(new DrawThread("Tom", ac, 800));
  t1.start();
  t2.start();
}
}

本文转自IT徐胖子的专栏博客51CTO博客，原文链接http://blog.51cto.com/woshixy/1058853如需转载请自行联系原作者

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