Question

我的问题是我的程序忽略了else语句。例如，用户没有在字段中输入任何内容并单击提交按钮，else下的语句应该执行。但它没有做它应该做的事情。我被困在这里，无法找到我的代码有什么问题。我试图在Eclipse中使用调试器调试它，它表明它仍然继续使用if语句下的语句，即使某些字段为空。

index.jsp文件：

<body>
<div id="mainContainer">
    <form action="processfare.jsp" method="post">
    <p>Enter passenger last name: <input type="text" name="lname" size="25"></p>
    <p>Enter passenger first name: <input type="text" name="fname" size="25"></p>
    <p>Destination: 
            <select name="dest" size="1">
            <option>Quezon Avenue</option>
            <option>GMA Kamuning</option>
            <option>Cubao</option>
            <option>Santolan</option>
            <option>Ortigas</option>
            <option>Shaw Boulevard</option>
            <option>Boni Avenue</option>
            <option>Guadalupe</option>
            <option>Buendia</option>
            <option>Ayala</option>
            <option>Magallanes</option>
            <option>Taft Avenue</option>
            </select></p>
    <p>Credit Card Number: <input type="text" name="ccnum" size="25"></p>
    <input type="submit" value="Submit">
</form>
</div>
</body>

processfare.jsp文件：

<body>
<%
  if (request.getParameter("lname") != null || request.getParameter("lname") != "" &&
   request.getParameter("fname") != null || request.getParameter("fname") != "" &&
   request.getParameter("dest") != null || request.getParameter("dest") != "" &&
   request.getParameter("ccnum").trim().length() > 0 ) {
      passBean.setLname(request.getParameter("lname"));
      passBean.setFname(request.getParameter("fname"));
      passBean.setDestination(request.getParameter("dest"));
      passBean.setCCnum(request.getParameter("ccnum")); 
              if (passBean.luhnTest(request.getParameter("ccnum"))==true){ %>
                <% passBean.procStation(); %>
                <%PDFDisplay.generatePDF(passBean); %>

                 <p>The fare amount to <%=passBean.dest %> from North Avenue Station is: P<%=passBean.fare %></p>
                 <p>Please remember to alight at <%=passBean.stop%></p><br>
                 <p>LIST OF FARE PROFITS</p>
                 <p>
                    TOTAL FARE FOR ALL STOP 1: P<%=passBean.totalFare1 %><br>
                    TOTAL FARE FOR ALL STOP 2: P<%=passBean.totalFare2 %><br>
                    TOTAL FARE FOR ALL STOP 3: P<%=passBean.totalFare3 %><br>
                    TOTAL FARE FOR ALL STOP 4: P<%=passBean.totalFare4 %><br>
                    TOTAL FARE FOR ALL STOP 5: P<%=passBean.totalFare5 %><br>
                    TOTAL FARE FOR ALL STOP 6: P<%=passBean.totalFare6 %>
                 </p>
                 <form action="index.jsp">
                    <input type="submit" value="<< GO BACK >>">
                 </form>
            <% } else { %>
              <p> Please enter a valid credit card number.</p>
              <p>Click <a href = "index.jsp">here</a> to try again.</p>
            <% } %> 

    <% } else {
          throw new ServletException ("Invalid input. Please try again");
     } %>

</body>

Answer 1

if (request.getParameter("lname") != null && request.getParameter("lname") != "" &&
   request.getParameter("fname") != null && request.getParameter("fname") != "" &&
   request.getParameter("dest") != null && request.getParameter("dest") != "" &&
   request.getParameter("ccnum").trim().length() > 0 ) {

你的＆＃34; ||＆＃34;正在创造一些奇怪的逻辑...

BTW xxx.trim（）。length（）＆gt; 0可能比！=＆＃34;＆＃34;

更好

Answer 2

您的所有OR（||）都应为AND（＆amp;＆amp;）。

    if ((request.getParameter("lname") != null) && (request.getParameter("lname") != "") &&
   (request.getParameter("fname") != null) && (request.getParameter("fname") != "") &&
   (request.getParameter("dest") != null) && (request.getParameter("dest") != "") &&
   request.getParameter("ccnum").trim().length() > 0 ) 

       {
        ***Reset of code follows here

Answer 3

你可以尝试像这样的if条件

if (request.getParameter("lname") != null && request.getParameter("lname") != "" && request.getParameter("fname") != null && request.getParameter("fname") != "" && request.getParameter("dest") != null && request.getParameter("dest") != "" && request.getParameter("ccnum").trim().length() > 0 ) {

Answer 4

您也可以为if添加括号：

if ((request.getParameter("lname") != null || request.getParameter("lname") != "") &&
   (request.getParameter("fname") != null || request.getParameter("fname") != "") &&
   (request.getParameter("dest") != null || request.getParameter("dest") != "") &&
   request.getParameter("ccnum").trim().length() > 0 )

如果else语句逻辑错误

4 个答案: