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NNTP-Posting-Date: Tue, 09 Aug 2011 12:25:30 -0500
Date: Tue, 09 Aug 2011 10:25:31 -0700
From: Patricia Shanahan <pats@acm.org>
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Subject: Re: setSize ArrayList, when will it come?
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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.

Patricia