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標 題Re: [問題] 請問有關JSP陣列的問題...
發信站SayYA 資訊站 (Thu Aug 31 18:17:55 2006)
轉信站ptt!ctu-reader!news.nctu!SayYa
※ 引述《[email protected] (kandy)》之銘言：
> <%
> String back_check[]=request.getParameterValues("yron");
> String back_ins_no[]=request.getParameterValues("ins_no");
[-----------]
這種寫法，不是翻到了古書。就是之前在學別的語言轉不過來XD
String[] foo的寫法比較好，也不會因為不同的ide出現不同莫名奇妙的error
> int i;
[----] 如果沒有特殊用途，local value儘量一開始就初始
可以寫在for之中 for(int i=0;...........)
> int size=9;
> for(i=0;i<size;i++)
> {
> if(back_check[i].equals("checked"))
[-----------] 你有把握每一個element都不是null嗎?
null的reference是不能被呼叫的。
來個簡單的實驗
public class NullCall {
public static void main(String[] args) {
String x = null;
x.equals("3");
}
}
=============================================
Exception in thread "main" java.lang.NullPointerException
at NullCall.main(NullCall.java:4)
> {
> out.println("back_ins_no[i]");
> }
> }
> %>
> ==========================================
> 執行後出現這訊息:
> HTTP Status 500 -
> --------------------------------------------------------------------------------
> type Exception report
> message
> description The server encountered an internal error () that prevented it
> from fulfilling this request.
> exception
> org.apache.jasper.JasperException: Exception in JSP: /Management/do.jsp:15
> 12: int size=9;
> 13: for(i=0;i<size;i++)
> 14: {
> 15: str=back_check[i];
> 16: if(str.equals("checked"))
> 17: {
> 18: out.println("back_ins_no[i]");
> Stacktrace:
> org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:504)
> org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
> org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
> org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
> javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
> root cause
> java.lang.NullPointerException
> org.apache.jsp.Management.do_jsp._jspService(do_jsp.java:61)
> org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
> javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
> org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:332)
> org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
> org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
> javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
> ========================================================================
> 請教各位前輩該怎麼解決,另外還有個問題..就是arrary的陣列個數要如何取得?
> 感謝大家!
*大驚*
array是java最初級物件了他有一個屬性是存長度的length
快找書去認識一下吧
> note The full stack trace of the root cause is available in the Apache
> Tomcat/5.5.17 logs.
> --------------------------------------------------------------------------------
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