class X{//定义锁对象private final ReentrantLock lock = new ReentrantLock();//...//定义需要保证线程安全的方法public void method() {//加锁
        lock.lock();try {//需要保证线程安全的代码
        }finally {//使用finally来保证释放锁
            lock.unlock();}}
}

public class Account {private String account;//账号private double balance;//余额//定义锁对象private final ReentrantLock lock = new ReentrantLock();public Account() {super();}public Account(String account, double balance) {super();this.account = account;this.balance = balance;}public void drawMoney(double drawMoney) {//加锁
        lock.lock();try {if(balance >= drawMoney) {System.out.println(Thread.currentThread().getName() + "取钱成功！吐出钞票：" + drawMoney);try {Thread.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}balance -= drawMoney;System.out.println("\t余额为：" + balance);}else {System.out.println(Thread.currentThread().getName() + "取钱失败！余额不足");}}finally {//放锁
            lock.unlock();}}public String getAccount() {return account;}public void setAccount(String account) {this.account = account;}public double getBalance() {return balance;}public void setBalance(double balance) {this.balance = balance;}
}

public class DrawThread extends Thread{private Account account;//模拟账户private double drawMoney;//当前取钱线程想要取的钱数public DrawThread(String name , Account account, double drawMoney) {super(name);this.account = account;this.drawMoney = drawMoney;}public void run() {account.drawMoney(drawMoney);}public static void main(String[] args) {Account account = new Account("123456" , 1000);new DrawThread("A", account, 800).start();new DrawThread("B", account, 800).start();}
}