Java 使用 double 或 float 时计算错误

Question

我正在尝试使用以下代码为 MVC 模式的模型部分创建一个 Web 应用程序:

    public OddsCalcBrain(String _odds, String _personalodds, String _bankroll){

    odds = Double.parseDouble(_odds);
    personalodds = Double.parseDouble(_personalodds) / 100.0d;
    personaloddslose = 1.0d-personalodds;
    bankroll = Double.parseDouble(_bankroll);

    result = bankroll * ((odds * personalodds - personaloddslose) / (2.0d * odds));
}

public String getResult(){
    return Double.toString(result);
}

我在 servlet 中使用 RequestDispatcher 将结果转发到 JSP 页面，如下所示:

     public void doGet(HttpServletRequest request,
         HttpServletResponse response)
 throws ServletException, IOException
 {
     String _personalodds = request.getParameter("personalodds");
     String _odds = request.getParameter("odds");
     String _bankroll = request.getParameter("bankroll");
     OddsCalcBrain brain = new OddsCalcBrain(_personalodds, _odds, _bankroll);

    request.setAttribute("result", brain.getResult());
    RequestDispatcher dispatcher=getServletContext().getRequestDispatcher("/oddscalc.jsp");
    dispatcher.forward(request, response);

 }

要打印它，我使用这个:

Result: ${result}

这个结果是非常错误的。例如，如果:

odds = 3;
personalodds = 0.5; //(The user would enter a percentage, so 50 would be 0.5)
personaloddslose = 0.5;
bankroll = 120;

该公式应生成 20.0 作为结果，如果我手动将其放入计算器中，它就会生成，但无论我使用 float 还是 double 作为变量，它都会生成 0.636。为什么会这样，我该如何正确地做到这一点？

Answer 1

您正在调用:

OddsCalcBrain brain = new OddsCalcBrain(_personalodds, _odds, _bankroll); 
//OddsCalcBrain("50", "3", "120");

而不是

OddsCalcBrain brain = new OddsCalcBrain(_odds, _personalodds, _bankroll);
//OddsCalcBrain("3", "50", "120");