Unchecked invocation sort(list) error... please help.

Question

this is the code I have problems with...
List contacts = Contact.search(searchParameters,
                              toContactTypeArray(
                                        contactSearchForm.getSelectedSearchLocations(),
                                        contactSearchForm.getContactTypeLocationDisplay()));
                         //todo alphabetize
                    Collections.sort(contacts);
the contact search was working fine until I added a sort to the code... now I get this message :
Type safety: Unchecked invocation sort(List) of the generic method sort(List<T>) of type
Collections
I am just taking over this project and It apears that the person before me used myEclipse to generate much of the code... I am having a hard time getting arround certain things like this.
Thanks for your help folks! Bryce.

Answer 1

Basically from what I read, your list needs to implement the Comparable class, and the elements in the list must all be comparable to each other (i.e. all strings, or all doubles, or all integers, or all a specific type of class or may have the same base class, etc.) If it's a custom list, try this (replace myContactTypeList with whatever your list class is named.)
List<myContactTypeList> contacts = Contact.search(searchParameters,
toContactTypeArray(
contactSearchForm.getSelectedSearchLocations(),
contactSearchForm.getContactTypeLocationDisplay()));
//todo alphabetize
Collections.sort(contacts);
You will pretty much always get a warning with generics. But, if you happen to do a clone of an ArrayList at any point, do this instead (it removes the warning, and should work...code hasn't been tested):
Iterator i = myOriginalList.iterator();
Double value; while((value = (Double) i.next()) != null) { DataList.add(value); }