Re: setSize ArrayList, when will it come?
On Tue, 9 Aug 2011, Patricia Shanahan wrote:
On 8/9/2011 9:58 AM, Roedy Green wrote:
...
Further, I would hope ArrayList.addAll would be smart enough to grow
the array only once, if needed.
...
It does the following:
1. Grow to the needed size.
2. Call the other collection's toArray method.
3. System.arraycopy the toArray result into the ArrayList's elementData.
This double copy is going to be faster than the one at a time approach
only if large numbers of nulls are being added. If that is the case, the
structure is probably too sparse for ArrayList to be a good choice.
It would be nice if ArrayList used a loop to do the copy for small added
collections; it could cut over to the array method for larger addends.
Anyway, with List.addAll and Collections.nCopies, we can write:
<T> void setSize(List<T> list, int size) {
int change = size - list.size();
if (change > 0) {
list.addAll(Collections.nCopies(change, null));
}
else if (change < 0) {
list.subList(size, list.size()).clear();
if (list instanceof ArrayList) ((ArrayList)list).trimToSize();
}
// else do nothing
}
I haven't tried that, but it should work.
So, Jan, less whining, more coding, please.
tom
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