设计一个java程序链接数据库实现模拟银行atm机

好的，下面是一个简单的Java程序实现模拟银行ATM机：

首先，我们需要创建一个ATM类，它代表了整个ATM机的控制器。在ATM类中，我们需要定义以下属性：

- cardNumber：表示插入的银行卡号码；
- cardPin：表示银行卡的密码；
- balance：表示银行卡的余额；
- isCardInserted：表示是否插入了银行卡；
- isPinValid：表示银行卡密码是否正确。

import java.sql.*;

public class ATM {
    private String cardNumber;
    private int cardPin;
    private double balance;
    private boolean isCardInserted;
    private boolean isPinValid;
    private Connection connection;

    public ATM() {
        isCardInserted = false;
        isPinValid = false;
        balance = 0;
    }

    public void insertCard(String cardNumber, int cardPin) {
        this.cardNumber = cardNumber;
        this.cardPin = cardPin;
        isCardInserted = true;
        validatePin();
    }

    public void ejectCard() {
        isCardInserted = false;
        isPinValid = false;
        cardNumber = "";
        cardPin = 0;
    }

    public void validatePin() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/atm", "root", "password");
            Statement stmt = connection.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM accounts WHERE card_number='" + cardNumber + "'");
            if (rs.next()) {
                int pin = rs.getInt("pin");
                if (pin == cardPin) {
                    isPinValid = true;
                    balance = rs.getDouble("balance");
                }
            }
            rs.close();
            stmt.close();
            connection.close();
        } catch (Exception e) {
            System.out.println(e);
        }
    }

    public void checkBalance() {
        if (isCardInserted && isPinValid) {
            System.out.println("Your balance is: " + balance);
        } else {
            System.out.println("Please insert your card and enter your PIN.");
        }
    }

    public void withdraw(double amount) {
        if (isCardInserted && isPinValid) {
            if (amount <= balance) {
                balance -= amount;
                try {
                    Class.forName("com.mysql.jdbc.Driver");
                    connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/atm", "root", "password");
                    Statement stmt = connection.createStatement();
                    stmt.executeUpdate("UPDATE accounts SET balance=" + balance + " WHERE card_number='" + cardNumber + "'");
                    stmt.close();
                    connection.close();
                } catch (Exception e) {
                    System.out.println(e);
                }
                System.out.println("You have withdrawn " + amount + ". Your new balance is " + balance + ".");
            } else {
                System.out.println("Insufficient funds. Your balance is " + balance + ".");
            }
        } else {
            System.out.println("Please insert your card and enter your PIN.");
        }
    }
}

在ATM类中，我们定义了以下方法：

- insertCard：插入银行卡，并验证密码；
- ejectCard：退卡；
- validatePin：验证密码是否正确；
- checkBalance：查询余额；
- withdraw：取款。

在validatePin方法中，我们通过JDBC连接到MySQL数据库，根据卡号从accounts表中查询密码和余额。如果密码正确，将isPinValid设置为true，并将余额设置为balance。

在withdraw方法中，我们首先检查卡是否插入并且密码是否正确。如果是，则检查余额是否足够取款。如果足够，则将余额减去取款金额，并将新的余额更新到数据库中。

下面是一个简单的测试程序，它创建一个ATM对象并模拟了一些操作：

import java.util.Scanner;

public class TestATM {
    public static void main(String[] args) {
        ATM atm = new ATM();
        Scanner scanner = new Scanner(System.in);

        System.out.println("Welcome to the ATM!");
        System.out.println("Please insert your card.");

        System.out.print("Enter card number: ");
        String cardNumber = scanner.nextLine();

        System.out.print("Enter PIN: ");
        int cardPin = scanner.nextInt();

        atm.insertCard(cardNumber, cardPin);

        while (true) {
            System.out.println("What would you like to do?");
            System.out.println("1. Check balance");
            System.out.println("2. Withdraw");
            System.out.println("3. Eject card");

            int choice = scanner.nextInt();

            switch (choice) {
                case 1:
                    atm.checkBalance();
                    break;
                case 2:
                    System.out.print("Enter amount to withdraw: ");
                    double amount = scanner.nextDouble();
                    atm.withdraw(amount);
                    break;
                case 3:
                    atm.ejectCard();
                    System.out.println("Thank you for using the ATM!");
                    System.exit(0);
                default:
                    System.out.println("Invalid choice. Please try again.");
                    break;
            }
        }
    }
}

这个程序模拟了一个ATM机的基本功能，包括插卡、验证密码、查询余额和取款。当用户选择退出时，程序将退卡并结束。