使用HTML表單（Java）中的變量執行計算時得到NaN結果

我試圖使用通過HTML表單提交的值來計算每月汽車貸款支付，該表單通過傳遞給使用Java類的servlet來提交與一個答案。每次我運行表單時，我都會得到NaN。使用HTML表單（Java）中的變量執行計算時得到NaN結果

形式：

<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);   
} 

}

對象：

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()); 

} 
}

來源

2017-04-18 emma

如果您可以告訴我們您的代碼中哪一行獲得NaN並且您當時使用了哪些輸入，那麼我們可以更容易地爲您提供幫助。 – DanielBarbarian

我認爲這個問題是在getPayment的最後一行（）。如果分母和分子均爲0.0，則會出現NaN錯誤。

您可以通過暫時返回一個固定值來查看NaN錯誤是否持續。

來源

2017-04-18 21:55:05 ptstone

使用HTML表單（Java）中的變量執行計算時得到NaN結果

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