Re: Inserting In a List
On 4/2/2013 8:04 PM, Joerg Meier wrote:
On Tue, 2 Apr 2013 22:52:20 +0000 (UTC), Martin Gregorie wrote:
On Tue, 02 Apr 2013 18:22:55 -0400, Eric Sosman wrote:
On 4/2/2013 5:06 PM, Martin Gregorie wrote:
[...]
Its also not clear to me whether the OP is expecting some form of
sorted list of filenames. If he is expecting that, it would be best to
use a TreeMap<String> rather than an ArrayList<String> to store the
filenames.
Is there a reason to prefer TreeMap (or other SortedMap) over
accumulate-disordered-and-sort-afterward?
I think so, yes, because none of File's list() and listFiles() methods
guarantee the order of the returned files. By using TreeMap or equivalent
the OP gets the sort for free, should it be required.
For free ? The cost is just distributed amongst the insert calls, and is
likely considerably higher than with an unsorted list that has a single
sort call once it is filled.
It is not that obvious to me that:
n O(1) + 1 O(nlogn) is that much faster than n log(n)
SortedMaps are for things that need sorting
accessible before all elements are inserted, which really isn't the case
here.
I use it a lot, both for that and because accessing stored objects by key
from a TreeMap is almost certainly faster than scanning an ArrayMap
unless it contains very few objects indeed.
Java doesn't have ArrayMaps. TreeMaps are O(log(n)) for get while a HashMap
alternative would be O(1). I don't think Java includes any map with
behaviour as ill coded as what you describe. Frankly, I'm having trouble
imagining any modern language having something quite that horrible. Even
LinkedList-Map-combinations usually are backed with some sort of HashMap.
I don't mean to be rude, but it seems like you have lot of misconception
about how data structures work in anything more than school/class level
implementations.
I think Martin has a lot of experience.
But I think he got this post garbled up a bit.
As you correctly state then there are no ArrayMap. I am not even sure
what such a beast would actually do.
I also somewhat suspect that he really meant TreeSet not TreeMap as
I can not see any key value pair here.
Arne