我想问
为什么我的程序中会触发java.lang.ClassCastException??
我不确定这是什么原因,
有人可以给我一些建议吗?
非常感谢!!!
<%@ page contentType="text/html; language=java"%>
<%@ page import="java.io.*" %>
<%@ page import="java.sql.*" %>
<%@ page import ="javax.sql.*" %>
<%@ page import="java.util.*" %>
<%@ page import="java.lang.*"%>
<%!
public class Goods implements Comparable{
private String Id = null;
private String name = null;
private float price = 0.00F;
private int number = 0;
private String percent = null;
public Goods(String Id,String name,float price,int number,String percent){
this.Id = Id;
this.name = name;
this.price = price;
this.number = number;
this.percent = percent;
}
public String getId()
{
return this.Id;
}
public String getName()
{
return this.name;
}
public float getPrice()
{
return this.price;
}
public int getNumber()
{
return this.number;
}
public String getPercent()
{
return this.percent;
}
public int compareTo(Object m)
{
Goods n = (Goods)m;
int comRs = Id.compareTo(n.Id);
return comRs;
}
}
%>
<%
String id = "Comp232";
String name = "OO_JAVA";
int number = 1;
float price= 222;
String percent = "85%";
Goods goods = new Goods(id,name,price,number,percent);
//Goods shop ;
ArrayList <Goods> ay = null;
if((ArrayList)session.getAttribute("car")==null)
{
ay = new ArrayList <Goods> ();
ay.add(goods);
session.setAttribute("car",ay);
}
else
{
ay=(ArrayList)session.getAttribute("car");
if(ay.isEmpty())
{
ay.add(goods);
session.setAttribute("car",ay);
//response.sendRedirect("order_index.jsp");
}
else
{
Iterator it = ay.iterator();
//Object shop1 = it.next();
for(int i = 0;i<ay.size();i++)
{
//this statement triggers java.lang.ClassCastException
//I am not sure what the problem
Goods shop = (Goods)it.next();
//System.out.println(shop);
}}}
/*
if(shop.compareTo(goods)==0)
{
out.println("textbook ordered");
}
else
{
ay.add(goods);
session.setAttribute("car",ay);
}
}
}
}
*/
%>
最佳答案
您需要使用Iterator<Goods>
.
Iterator<Goods> it = ay.iterator();
此外,您还可以使用 foreach 循环而不是使用迭代器。从功能上来说,它是一样的,但在语义上更清晰。
for (Goods g in ay) {
// do stuff
}
最后,我认为
ay=(ArrayList)session.getAttribute("car");
应该是
ay = (ArrayList<Goods>)session.getAttribute("car");
关于java.lang.ClassCastException问题,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/4795435/