如何用Java编程语言来设计和实现一个基础的银行ATM（自动取款机）系统？

设计一个基本的银行ATM系统，我们可以使用Java来创建几个类来模拟机器的功能和用户交互。以下是一个简单的示例：

1. **Account** 类：代表用户的账户，包含账户余额、户名等属性。

public class Account {
    private double balance;
    private String holderName;

    public Account(double initialBalance, String name) {
        this.balance = initialBalance;
        this.holderName = name;
    }

    // getters and setters...
    public double getBalance() { return balance; }
    public void deposit(double amount) { balance += amount; }
    public void withdraw(double amount) {
        if (amount <= balance) {
            balance -= amount;
        } else {
            System.out.println("Insufficient balance.");
        }
    }
}

2. **ATM** 类：作为银行ATM的实体，负责与用户交互并处理操作。

import java.util.Scanner;

public class ATM {
    private Account account;

    public ATM(Account account) {
        this.account = account;
    }

    public void startSession() {
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.println("Select an option:");
            System.out.println("1. Check Balance");
            System.out.println("2. Deposit");
            System.out.println("3. Withdraw");
            System.out.println("4. Exit");

            int choice = scanner.nextInt();
            switch (choice) {
                case 1:
                    displayBalance();
                    break;
                case 2:
                    handleDeposit(scanner.nextDouble());
                    break;
                case 3:
                    handleWithdraw(scanner.nextDouble());
                    break;
                case 4:
                    System.out.println("Thank you for using the ATM. Goodbye!");
                    return;
                default:
                    System.out.println("Invalid choice. Please try again.");
            }
        }
    }

    private void displayBalance() {
        System.out.printf("Your current balance is %.2f\n", account.getBalance());
    }

    private void handleDeposit(double amount) {
        account.deposit(amount);
        displayBalance();
    }

    private void handleWithdraw(double amount) {
        account.withdraw(amount);
        displayBalance();
    }
}

3. **Main** 类用于测试ATM。

public class Main {
    public static void main(String[] args) {
        Account userAccount = new Account(5000, "John Doe");
        ATM atm = new ATM(userAccount);
        atm.startSession();
    }
}

在这个例子中，用户通过ATM选择操作，如查看余额、存款和取款。ATM会根据用户输入执行相应的账户操作。