Java ArrayLists

**theGlitch** · December 3rd, 2009, 05:47 PM

Hey all. I'm working on an application that will take an ArrayList filled with objects and parse the objects into an xml document. My issue is, the objects I'm trying to access are losing their type by being added to my ArrayList.

In other words I'm adding a Change object to my ArrayList. When I try to access it later it reads it as a plain Object.

Code:

currentSVR = Change.getServer(stripped.get(0));

throws:

getServer(myproject.Change) in myproject.Change cannot be applied to (java.lang.Object)

Everything is in the same package and works otherwise.

**amtrac24** · December 3rd, 2009, 11:14 PM

im a .net guy but i believe array lists in java are exactly the same.
An array list contains a list of objects. So when you grab the item from the arraylist you will need to cast it back into whatever type it is. Otherwise it will come back as an object.

You would want to stay away from bringing everything back as objects cause it will be late bound (in .net atleast I assume its the same as Java)

What does the getServer function take as a parameter? As specific object type or just an object?

**theGlitch** · December 4th, 2009, 09:41 AM

Code:

public static String getServer (Change c){
                  String server = c.s;
                  return server;
          }

so if I understand you correctly, the following should work

Code:

currentSVR = Change.getServer((Change)stripped.get(0));

**amtrac24** · December 4th, 2009, 09:56 AM

the only time it wouldn't work is if the arraylist contains an object that is not a "Change".

Instead of using an arraylist use a linked list or an array of "change". This will verify that everything in the list will be of type "change".

**theGlitch** · December 9th, 2009, 01:30 PM

the problem with using a regular array is that it needs to be dynamic. I won't know how many Change objects I'll need.

EDIT:
Linked Lists don't seem to hold the type either.

**Is_It_Just_Me?** · December 10th, 2009, 07:05 AM

Use Generics.

For example:

Code:

ArrayList<Change> a = new ArrayList<Change>();

This will allow for the Change objects added to the ArrayList to retain their type, so you don't have to do any casting.

You can also use generics for LinkedLists.