Re: Generics in Arrays

From:
"Oliver Wong" <owong@castortech.com>
Newsgroups:
comp.lang.java.help
Date:
Thu, 07 Sep 2006 17:46:04 GMT
Message-ID:
<wVYLg.10231$Mh7.795@edtnps90>
"Wojtek Bok" <wb@nospam.com> wrote in message
news:1WXLg.11099$Hr1.688@clgrps12...

If I have a ArrayList which will hold items of type MyItem, then I declare
it as:
-----------------------------------------------------------
ArrayList<MyItem> items = new ArrayList<MyItem>();
-----------------------------------------------------------

I then have a ArrayList which holds these items:
-----------------------------------------------------------
ArrayList<ArrayList<MyItem>> allItems = new
ArrayList<ArrayList<MyItem>>();
-----------------------------------------------------------

I can then get an array of the items as:
-----------------------------------------------------------
ArrayList[] itemList = allItems.toArray(new ArrayList[0]);
-----------------------------------------------------------

Ok, now to get at each ArrayList<MyItem> I should be able to:
-----------------------------------------------------------
ArrayList<MyItem> itemArray;
for ( int c = 0; c < itemList.length; c++ )
  itemArray = itemList[c];
-----------------------------------------------------------

Except that the compiler complains about type safety in the last line.
Fair enough, I have an generic ArrayList I am trying to put into an
ArrayList<MyItem>.

So how do I keep the compiler happy (other than add suppress warnings
"unchecked" for the entire method)?

I tried:
-----------------------------------------------------------
ArrayList<MyItem>[] itemList = allItems.toArray(new ArrayList<MyItem>[0]);
-----------------------------------------------------------
 but that causes other errors.


    Why are you bringing arrays into the situation?

ArrayList<ArrayList<MyItem>> allItems = new ArrayList<ArrayList<MyItem>>();
for (ArrayList<MyItem> itemList : allItems) {
  /*do something with each item list*/
}

    - Oliver

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