用MVC写一个贷款计算程序

在MVC（Model-Controller）架构中编写贷款计算程序通常会将程序分为三个部分：

1. **Model**（模型）：负责数据处理和业务逻辑。在这个场景下，模型会包含贷款相关的数据结构，如贷款金额、利率、还款期限等，并定义计算月供、总利息等方法。例如：

public class LoanCalculator {
    private double loanAmount;
    private double annualInterestRate;

    // 构造函数和getter/setter...
    public double calculateMonthlyPayment() {
        // 计算公式，比如使用等额本息法
        double monthlyRate = annualInterestRate / 12 / (1 - Math.pow(1 + annualInterestRate / 12, -loanTermInYears * 12));
        return loanAmount * monthlyRate / (1 - Math.pow(1 + monthlyRate, -loanTermInYears * 12));
    }

    // 其他计算方法...
}

2. **View**（视图）：显示用户界面，接收用户输入并展示计算结果。这可以是一个简单的控制台应用或GUI界面。例如，在控制台上：

public class ConsoleLoanCalculatorView {
    public void displayInstructions() {
        System.out.println("请输入贷款金额、年利率和贷款年限:");
    }

    // 接收用户输入并调用模型计算...
    public void displayMonthlyPayment(double loanAmount, double interestRate, int loanYears) {
        LoanCalculator model = new LoanCalculator();
        double payment = model.calculateMonthlyPayment();
        System.out.printf("每月应还:%.2f\n", payment);
    }
}

3. **Controller**（控制器）：连接模型和视图，处理用户的交互请求。它从视图获取输入，更新模型，然后通知视图显示新的信息。例如：

public class LoanCalculatorController {
    private ConsoleLoanCalculatorView view;
    private LoanCalculator model;

    public LoanCalculatorController(ConsoleLoanCalculatorView view) {
        this.view = view;
    }

    public void run() {
        view.displayInstructions();
        // 用户输入处理...
        double loanAmount = getLoanAmountFromUser();
        double interestRate = getAnnualInterestRateFromUser();
        int loanYears = getLoanYearsFromUser();

        model = new LoanCalculator(loanAmount, interestRate);
        view.displayMonthlyPayment(loanAmount, interestRate, loanYears);
    }
}