Question

我尝试使用通过HTML表单提交的值计算月度汽车贷款，这些值传递给使用Java类提供答案的servlet。每次我运行表单时，我都会得到NaN。

表格：

<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>Car Loan</title>
</head>
<body>
    <h1>Car Loan Calculator</h1>

    <form method = "get" action = "CalcPayment">
        <label> APR: </label><input type ="text" name ="apr"><br>
        <label> Term (in years): </label><input type ="text" name 
         ="term"><br>
        <label> Principal: </label><input type ="text" name 
       ="principal"><br>

        <input type="submit" value ="Get Loan Payment">
     </form>
    <p>
       Loan payment is: ${carLoan.getPayment()}
    </p>
</body>
</html>

的Servlet

@WebServlet(name = "CalcPayment", urlPatterns = {"/CalcPayment"})
public class CalcPayment extends HttpServlet {


@Override
protected void doGet(HttpServletRequest request, HttpServletResponse 
response)
        throws ServletException, IOException {
    PrintWriter out = response.getWriter();
    String strApr = request.getParameter("apr");
    String strTerm = request.getParameter("term");
    String strPrincipal = request.getParameter("principal");
    int apr, term;
    double principal; 
    CarLoan loanPay;


        apr = Integer.parseInt(strApr);
        term = Integer.parseInt(strTerm);
        principal = Double.parseDouble(strPrincipal);


    loanPay = new CarLoan (apr, term,  principal);


    request.setAttribute("carLoan",loanPay);
    request.getRequestDispatcher("/index.jsp").forward(request, 
response);        
 }

}

对象：

package pojos;

public class CarLoan {
private int apr, term;
private double principal;


public CarLoan (){
    this.apr = 0;
    this.term = 0;
    this.principal = 0;
}

public CarLoan(int apr, int term, double principal) {
    this.setApr(apr);
    this.setTerm(term);
    this.setPrincipal(principal);
}

public double getApr() {

    return apr;
}

public void setApr(int apr) {
    if(apr >= 0 && apr <= 30){
       this.apr = apr;         
    }
    else{
        throw new IllegalArgumentException("APR must be between 0 and 
30");
    }
}


public double getTerm(){
    return term;
}

public void setTerm(int term) {

    if(term>=1 && term<=6){
       this.term = term*12;  
    }
    else{
        throw new IllegalArgumentException("Loan term must be between 1 
"
                + "and 6");
    }
}


public double getPrincipal(){
    return principal;
}

public void setPrincipal(double principal) {

    if(principal>=0){
       this.principal = principal;  
    }
    else{
        throw new IllegalArgumentException("Principal amount cannot be  
+ "negative");
    }
}


public double getPayment(){

    double r = ((this.apr/100)/12);
    double denominator = (Math.pow(1+r, this.term) - 1);
    double numerator=  (r * Math.pow(1 + r, this.term));

    return (numerator/denominator);
}

@Override
public String toString() {
    return String.format("rate= %d term=%d principal=%.2f", this.apr, 
            this.term, this.principal,+ this.getPayment());

}
}

Answer 1

我认为问题出在getPayment（）的最后一行。如果分母和分子都是0.0，则会出现NaN错误。

您可以通过暂时返回固定值来尝试，以查看NaN错误是否仍然存在。

使用HTML表单（Java）中的变量执行计算时获取NaN结果

1 个答案: