一个数组中的数据如何循环出来？

Question

我接下来是这样写的；
java.lang.Object []obj=col.toArray();
这样写好象不行啊，提示出错，

Answer 1

写错了：
==============
我接下来是这样写的；
java.lang.Object []obj=al.toArray();
这样写好象不行啊，提示出错，

Answer 2

public Object[] toArray(Object[] a)用这个呢？

Answer 3

for (int i=0;i<al.size();i++) {
   System.out.println(al.get(i);
}

Answer 4

楼上的错误：
java.lang.NullPointerException
at _admin._gzxx._P040201._jspService(P040201.jsp:80)
[/admin/gzxx/P040201.jsp]
at oracle.jsp.runtime.HttpJsp.service(HttpJsp.java:139)
at oracle.jsp.runtimev2.JspPageTable.service(JspPageTable.java:317)
at oracle.jsp.runtimev2.JspServlet.internalService(JspServlet.java:465)
at oracle.jsp.runtimev2.JspServlet.service(JspServlet.java:379)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at com.evermind[Oracle9iAS (9.0.3.0.0) Containers for J2EE].server.http.ServletRequestDispatcher.invoke(ServletRequestDispatcher.java:721)
at com.evermind[Oracle9iAS (9.0.3.0.0) Containers for J2EE].server.http.ServletRequestDispatcher.forwardInternal(ServletRequestDispatcher.java:306)
at com.evermind[Oracle9iAS (9.0.3.0.0) Containers for J2EE].server.http.HttpRequestHandler.processRequest(HttpRequestHandler.java:767)
at com.evermind[Oracle9iAS (9.0.3.0.0) Containers for J2EE].server.http.HttpRequestHandler.run(HttpRequestHandler.java:259)
at com.evermind[Oracle9iAS (9.0.3.0.0) Containers for J2EE].server.http.HttpRequestHandler.run(HttpRequestHandler.java:106)
at EDU.oswego.cs.dl.util.concurrent.PooledExecutor$Worker.run(PooledExecutor.java:803)
at java.lang.Thread.run(Thread.java:536)

Answer 5

你这样试试：
java.util.ArrayList al=(java.util.ArrayList)request.getAttribute("guide2");
Iterator iterator = al.iterator();
while(iterator.hasNext()){
    System.out.println((String)iterator.next());//这里假设你的al里存的是String 类型的对象
}

Answer 6

java.lang.NullPointerException
at _admin._gzxx._P040201._jspService(P040201.jsp:80)
[/admin/gzxx/P040201.jsp]
at oracle.jsp.runtime.HttpJsp.service(HttpJsp.java:139)
at oracle.jsp.runtimev2.JspPageTable.service(JspPageTable.java:317)
at oracle.jsp.runtimev2.JspServlet.internalService(JspServlet.java:465)
at oracle.jsp.runtimev2.JspServlet.service(JspServlet.java:379)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at com.evermind[Oracle9iAS (9.0.3.0.0) Containers for J2EE].server.http.ServletRequestDispatcher.invoke(ServletRequestDispatcher.java:721)
at com.evermind[Oracle9iAS (9.0.3.0.0) Containers for J2EE].server.http.ServletRequestDispatcher.forwardInternal(ServletRequestDispatcher.java:306)
at com.evermind[Oracle9iAS (9.0.3.0.0) Containers for J2EE].server.http.HttpRequestHandler.processRequest(HttpRequestHandler.java:767)
at com.evermind[Oracle9iAS (9.0.3.0.0) Containers for J2EE].server.http.HttpRequestHandler.run(HttpRequestHandler.java:259)
at com.evermind[Oracle9iAS (9.0.3.0.0) Containers for J2EE].server.http.HttpRequestHandler.run(HttpRequestHandler.java:106)
at EDU.oswego.cs.dl.util.concurrent.PooledExecutor$Worker.run(PooledExecutor.java:803)
at java.lang.Thread.run(Thread.java:536)

Answer 7

al绝对不是空，但用：al.toArray();时候就为空了

Answer 8

这几天CSDN有没有高手在啊，晕死，什么问题都解决不了？

Answer 9

java.util.ArrayList al=(java.util.ArrayList)request.getAttribute("guide2");
Iterator iterator = al.iterator();
while(iterator.hasNext()){
    System.out.println((String)iterator.next());//这里假设你的al里存的是String 类型的对象
}
这样就行了，不用java.lang.Object []obj=col.toArray();

Answer 10

<%
for (int i=0;i<al.size();i++) {
Map map = (Map)al.get(i);
//ID
String s_Id = (String)map.get("s_Id");
//名称
String s_Name = (String)map.get("s_Name");
%>