为什么不能赋值?

Question

字符串比较用equals()方法
if (strFlagDelete.equals("on"))
{}

Answer 1

也就是说，你的代码根本就不符合if判断的条件，所以if里面的语句都不执行！

Answer 2

当我改成equals或者equalsIgnoreCase都会出现下面的出错信息，又没有error，为什么？
A Servlet Exception Has Occurred
Exception Report:
javax.servlet.ServletException
at org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:481)
at system.user._0002fsystem_0002fuser_0002fgroupuser_00031_0002ejspgroupuser1_jsp_38._jspService(_0002fsystem_0002fuser_0002fgroupuser_00031_0002ejspgroupuser1_jsp_38.java:183)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:119)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.jasper.servlet.JspServlet$JspServletWrapper.service(JspServlet.java:184)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:328)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:407)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:215)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:251)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:977)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:196)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:977)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2041)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161)
at org.apache.catalina.valves.ValveBase.invokeNext(ValveBase.java:242)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:414)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:975)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:159)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:977)
at org.apache.catalina.connector.http.HttpProcessor.process(HttpProcessor.java:818)
at org.apache.catalina.connector.http.HttpProcessor.run(HttpProcessor.java:897)
at java.lang.Thread.run(Thread.java:484)Root Cause:
java.lang.NullPointerException
at system.user._0002fsystem_0002fuser_0002fgroupuser_00031_0002ejspgroupuser1_jsp_38._jspService(_0002fsystem_0002fuser_0002fgroupuser_00031_0002ejspgroupuser1_jsp_38.java:107)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:119)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.jasper.servlet.JspServlet$JspServletWrapper.service(JspServlet.java:184)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:328)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:407)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:215)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:251)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:977)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:196)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:977)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2041)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161)
at org.apache.catalina.valves.ValveBase.invokeNext(ValveBase.java:242)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:414)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:975)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:159)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:977)
at org.apache.catalina.connector.http.HttpProcessor.process(HttpProcessor.java:818)
at org.apache.catalina.connector.http.HttpProcessor.run(HttpProcessor.java:897)
at java.lang.Thread.run(Thread.java:484)

Answer 3

对象比较要用equals()函数，只用基本类型的才可以用“==”

Answer 4

if (strFlagDelete!=null&&strFlagDelete.equals("on"))也不知道你的vd 又没有new 过

Answer 5

nDelete++;
 User ud=new User(strUserId);
 vd.addElement(ud);
 User ud1=new User();
 ud1=ud.doLoad();
 strDeleteIdList+=ud1.getUserId()+",";
 strDeleteNameList+=ud1.getUserName()+",";中有一个为null，你自己检查一下，那个可能为null值的

Answer 6

<%@ page contentType="text/html; charset=gb2312" %>
<%@ page import="fsoa.com.system.*"%>
<%@ page import="java.util.*"%>
<%@ page import="fsoa.com.exception.*"%>
<HTML>
<HEAD>
<TITLE> 用户管理 </TITLE>
<%
User u=new User();
u.setOrganizeId("0000"); Vector vc=u.getAllOrganize();
%>
<%!
    Vector vd=new Vector();
String strDeleteIdList="";
String strDeleteNameList="";
%>

</HEAD><BODY>
  <FORM METHOD=POST name="frm" ACTION="adduser.jsp">
  <div>
    <TABLE>
    <TR>
     <TD width="10%"></TD>
     <TD width="20%">用户编号</TD>
     <TD width="20%">用户名称</TD>
     <TD width="20%">用户类型</TD>
     <TD width="20%">担任角色</TD>
<TD width="10%">详细情况</TD>
    </TR>
  <% for(int i=0;i<vc.size();i++){
  u=(User)vc.get(i);
  String strUserId=u.getUserId();
  String strUserName=u.getUserName();
  String strUserType=u.getUserType();
  String strUserRole=u.getRoleId();
  int nDelete=0;  %>
    <TR>
     <TD><INPUT TYPE="checkbox" NAME="flagdelete"></TD>
  <% String strFlagDelete=request.getParameter("flagdelete");
  if (strFlagDelete!=null&&strFlagDelete.equals("on")){
 nDelete++;
 User ud=new User(strUserId);
 vd.addElement(ud);
 User ud1=new User();
 ud1=ud.doLoad();
 strDeleteIdList+=ud1.getUserId()+",";
 strDeleteNameList+=ud1.getUserName()+","; }
  %>
     <TD><%=strUserId%></TD>
     <TD><%=strUserName%></TD>
     <TD><%=strUserType%></TD>
     <TD><%=strUserRole%></TD>
<TD><INPUT TYPE="button" value=" >>>> "></TD>
<INPUT TYPE="hidden" name="DeleteIdList" value="<%=strDeleteIdList%>">
<INPUT TYPE="hidden" name="DeleteNameList" value="<%=strDeleteNameList%>">
    </TR>
<%}%>
    </TABLE>
<tr><BR><BR></tr>
</div>
<div>
  <TABLE>
   <TR align="center">
    <TD width="50%"></TD>
    <TD width="18%"><INPUT TYPE="button" value="  增加  "  Onclick = "javascript:o()"></TD>
    <TD width="18%"><INPUT TYPE="button" value="  删除  "  Onclick = "javascript:deleteu('<%=strDeleteNameList%>')"></TD>
<TD width="18%"><INPUT TYPE="button" value="  取消  "></TD>
   </TR>
   </TABLE> </div>

  </FORM>
</BODY>
</HTML>
<SCRIPT LANGUAGE="JavaScript">
<!--
function o(){
 window.close();
 window.open('adduser.jsp');
 }
//-->
</SCRIPT>
<SCRIPT LANGUAGE="JavaScript">
<!--
function deleteu(strDeleteIdList){
  window.alert(strDeleteIdList);
}
//-->
我干脆把整个jsp贴出来,if (strFlagDelete!=null&&strFlagDelete.equals("on"))这一句也试过不行,大家看看还有什么问题,小弟是新手,写得不好大家不要见笑.

Answer 7

当strFlagDelete==null时就执行下面的赋值！

Answer 8

<TD><INPUT TYPE="checkbox" NAME="flagdelete"></TD>
  <% String strFlagDelete=request.getParameter("flagdelete");
这两句有问题吗?