ClassCastException - don't know why

[hibbert]

Hey there,
i've got a problem, and i don't know why... i try to explain my little problem:

i've got a ListField with a listcallback (ListCallback2), a vector (named _messages) of my own Class MyOrder. Now I want to draw all Items of the Vector into the ListField. Here is some of my sourcecode:
MyOrder-Class

PHP Code:

public class MyOrder {
    private int status;
    private String ursprung;
//... 


mainScreen with the ListCallback and ListField

PHP Code:

private static Vector _messages;
    public static ListField _listField;
    public static ListCallback2 callback;
//...
    _listField = new ListField();
    callback = new ListCallback2();
    _listField.setCallback(callback);
//...
public static MyOrder getOrder(int id) {
    MyOrder dummy = (MyOrder)_messages.elementAt(id);
    return dummy;
}
//...
private class ListCallback2 implements ListFieldCallback {
        public Vector listElements = new Vector();
        
        public void drawListRow(ListField list, Graphics g, int index, int y, int w) {
            String text = "dummy";
            String text2 = (String)listElements.elementAt(index);
            try {
                MyOrder myDummy = new MyOrder();
                myDummy = (MyOrder)getOrder(index); // <--------- error here
                text2 = "OK";
            } catch (Exception ex) {
                System.out.println("Fehler:> "+ex);
            }
            
            text = _messages.size() + "|"+_messages.capacity()+"|"+index+"|"+text2;

            g.drawText(text, 15, y, 0, w);
        } 


In the marked line i get a ClassCastException - Error, but i dont know why...
I tried it with / without (MyOrder) and with / without new MyOrder()

so how do i get the Object from the index i want to?

tahnks hibbert

[hrbuckley]

I would guess that you are putting an object on the list that is not a subclass of MyOrder. What I would do (other than check the code that loads the list) is change getOrder(int id) to:

public static MyOrder getOrder(int id) {
    Object obj = _messages.elementAt(id);
    MyOrder dummy = (MyOrder)obj; // <--- put break point here
    return dummy;
}

Put a break point where indicated and inspect obj to find out what its class is. That will (hopefully) suggest the next step.

[holy3daps]

Hi!

You might also try:

Object obj = getOrder(index);
if (obj instanceof MyOrder)
{
    MyOrder order = (MyOrder)obj;
}
else
{
    // show some indication of why it failed
    if (null == obj)
    {
        // you now know that there is no object at index "index"
    }
    else
    {
        String className = obj.getClass().getName();
        // you will now know what the object's class is
        // and hopefully you can track down how it got there
    }
}

This should give you an idea of what's actually going on.

Question: why are you doing the following:

MyOrder myDummy = new MyOrder();
myDummy = (MyOrder)getOrder(index);

? You're wiping out the "new MyOrder()" in the very next line, so there's no need to create a new one, unless the constructor is caching it somewhere else, which is a rather interesting design for your MyOrder class.

Cheers,

karl