创建一个Java程序，实现银行存取款功能。要求1.创建账户，初始存款

为0；2.实现存款、取款、查询余额功能；3.考虑多线程并发操作问题。

代码如下：

import java.util.concurrent.locks.ReentrantLock;

public class BankAccount {
    private String accountNumber; //账户号码
    private double balance; //账户余额
    private ReentrantLock lock; //重入锁

    public BankAccount(String accountNumber) {
        this.accountNumber = accountNumber;
        this.balance = 0;
        this.lock = new ReentrantLock();
    }

    //存款
    public void deposit(double amount) {
        lock.lock(); //加锁
        try{
            balance += amount;
            System.out.println(Thread.currentThread().getName() + " 存款 " + amount + " 元，余额 " + balance + " 元。");
        }finally {
            lock.unlock(); //解锁
        }
    }

    //取款
    public void withdraw(double amount) {
        lock.lock(); //加锁
        try{
            if(balance >= amount){
                balance -= amount;
                System.out.println(Thread.currentThread().getName() + " 取款 " + amount + " 元，余额 " + balance + " 元。");
            }else{
                System.out.println(Thread.currentThread().getName() + " 余额不足，无法取款！");
            }
        }finally {
            lock.unlock(); //解锁
        }
    }

    //查询余额
    public double getBalance() {
        return balance;
    }
}

主程序如下：

public class Main {
    public static void main(String[] args) {
        //创建账户
        BankAccount account = new BankAccount("123456");

        //创建存款线程
        Thread depositThread1 = new Thread(() -> {
            account.deposit(1000);
        }, "存款线程1");
        Thread depositThread2 = new Thread(() -> {
            account.deposit(2000);
        }, "存款线程2");

        //创建取款线程
        Thread withdrawThread1 = new Thread(() -> {
            account.withdraw(500);
        }, "取款线程1");
        Thread withdrawThread2 = new Thread(() -> {
            account.withdraw(1500);
        }, "取款线程2");

        //启动线程
        depositThread1.start();
        depositThread2.start();
        withdrawThread1.start();
        withdrawThread2.start();

        //等待线程执行完毕
        try {
            depositThread1.join();
            depositThread2.join();
            withdrawThread1.join();
            withdrawThread2.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        //查询余额
        System.out.println("账户余额为：" + account.getBalance() + " 元。");
    }
}

运行结果如下：

存款线程1 存款 1000.0 元，余额 1000.0 元。
存款线程2 存款 2000.0 元，余额 3000.0 元。
取款线程1 取款 500.0 元，余额 2500.0 元。
取款线程2 取款 1500.0 元，余额 1000.0 元。
账户余额为：1000.0 元。