Cast from an Object to a primitive long

[Natalie Kopple]

I posted a question before; but, that question was completely misleading. I feel sorry for that.

Let me try to do it better.

.....
private long[] selectedUserIDs;
 
// there is a method to return a SelectedUserField, which is a Map
public long[] getSelectedUserIDs()
{
   List the UserIDList= new ArrayList();
 
   Iterator i = selectedUserFieldMap.values().iterator();
   while( i.hasNext() )
   {
      SelectedUserField selectedUserField = ( SelectedUserField ) i.next();
      if ( selectedUserField.isSelected() )
      { 
         the UserIDList.add( selectedUserField.getId() );
      }
      // the statement below is my question: to cast a List to long[]
      return (????) theUserIDLIst.toArray( new ???[ theUserIDList.size() ] );
   }
}

[Richard Green]

return (long[])theUserIDList.toArray(new long[theUserIDList.size()]);

[Ernest Friedman-Hill]

Originally posted by Lynette Dawson:
return (long[])theUserIDList.toArray(new long[theUserIDList.size()]);

Well... no. The argument to toArray() is an Object array, not a long[] or other primitive array type. As I think I told you earlier today: allocate your array of longs, assign each one, one at a time. You could do it with direct assignment in Java 5 due to autoboxing; otherwise, you'll have to call longValue() on your longs explicitly.

[Garrett Rowe]

Well... no. The argument to toArray() is an Object array, not a long[] or other primitive array type. As I think I told you earlier today: allocate your array of longs, assign each one, one at a time. You could do it with direct assignment in Java 5 due to autoboxing; otherwise, you'll have to call longValue() on your longs explicitly.

Incidentally as an excersise in redundancy, I just wrote a class of static utility method for just that purpose, although I'm sure there's a library out there that does this already.

public final class ArrayConverter
{
   public static Integer[] convert(final int [] arr)
   {
      //...
   }
 
   public static int[] convert(final Integer[] arr)
   {
      //..
   }
 
   public static Long[] convert(final long[] arr)
   {
      //...
   }
   
   //... etc.