Question

我一直在Java上得到这个错误

org.apache.jasper.JasperException：java.lang.NullPointerException

我想要做的是在netbeans 8.1上运行JSP页面。基本上尝试获取sqrt的上限和下限函数域并将其显示在表上。但是当我运行该程序时，我不断在页面上收到该错误。我花了几个小时试图解决它，但我卡住了。任何帮助都会很好。

<%-- 
Document   : Lab 4 - Test cases
Created on : Jan 30, 2016, 6:28:25 PM
Author     : David Adade
--%>
<%@page import="lu.engi3255.dadade.lab4.Numerical"%>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@ page import = "java.util.Map" %>
<%@page import="java.util.*" %>
<!DOCTYPE html>

<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
    <title>Math Page</title>
</head>
<body>
    <h1>Math Page 1</h1>
    <%
        String x0, x1, n;
        double x, inc;

        x0 = request.getParameter("x0");
        x1 = request.getParameter("x1");
        n = request.getParameter("n");
        double lowerbound = Double.parseDouble(x0);
        double upperbound = Double.parseDouble(x1);
        double domain;
        int num = Integer.parseInt(n);
        if (x0 == null) {%>
    <p>x0 has to be a number</P>
        <%
        } else {
            try {
                lowerbound = Double.parseDouble(x0);
            } catch (NumberFormatException e) {
                n = null;
        %>
    <p>x0 has to be a number1</p>
    <% }
        }
        if (x1 == null) {
    %>
    <P>x1 is invalid</p>
        <% } else {
            try {
                upperbound = Double.parseDouble(x1);
            } catch (NumberFormatException e) {
                x1 = null;

        %>
    <p>x1 has to be a number </p>
    <% }
        }
        if (n == null) {
    %>

    <p>n is invalid</p>
    <% } else {
            try {
                num = Integer.parseInt(n);
            } catch (NumberFormatException e) {
                n = null;
            }
        }
    %>
    <p>n has to be a number</p>
    <%
        if (lowerbound < 0) {
    %>
    <p>lowerbound has to be greater than 0</p>
    <% }
                if (lowerbound == upperbound) {
                }%>
    <p> Lowerbound not equal </p>
    <% if ( n != null && x0 != null && x1 != null){
        num = Integer.parseInt(n);
        lowerbound = Double.parseDouble(x0);
        upperbound = Double.parseDouble(x1);


      //  inc /= num - 1;

    %>
    <p> invalidentry</p>
    <% if (num > 0 && upperbound <= 1) { %>
    <table>
        <thead>
            <tr>
                <th>x</th>
                <th> y = sqrt(x) +100</th>
            </tr>
        </thead>
        <tbody>
            <%                    for (int i = 0; i < num; i++) {

            %>

            <tr>
                <td><% out.println(String.format("%.3f", lowerbound)); %></td>
                <td><% out.println(String.format("%.3f", (Math.sqrt(upperbound)))); %></td>
                <% lowerbound = Math.sqrt(lowerbound) + (100);
                    }

                    }
                }%>
            </tr>


            </tbody>
        </table>
    </body>
</html>

这是我第一次使用netbeans，而且我是二年级学生，所以可能会有很多错误。

继续得到Null Java错误

0 个答案: