Path: csiph.com!eternal-september.org!feeder.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Martin Gregorie Newsgroups: comp.lang.java.programmer Subject: Re: How to parse an array? Date: Mon, 26 Jun 2017 15:47:23 -0000 (UTC) Organization: A noiseless patient Spider Lines: 52 Message-ID: References:

<1758ec6f-966d-44c2-bdb9-03e5d4b61619@googlegroups.com> <21b6dbae-d72c-446d-b272-bac67bc7fd86@googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Mon, 26 Jun 2017 15:47:23 -0000 (UTC) Injection-Info: mx02.eternal-september.org; posting-host="bd9c564d5e0e09d99abbff91f4050575"; logging-data="18957"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18z2Q4ozEzijyQB8MWx3JCN7EalNC/pUnQ=" User-Agent: Pan/0.141 (Tarzan's Death; 168b179 git.gnome.org/pan2) Cancel-Lock: sha1:FWViBOpmY4raeju8HK4SYC1GyRo= Xref: csiph.com comp.lang.java.programmer:36733 On Mon, 26 Jun 2017 07:47:19 -0700, Eric Douglas wrote: > On Monday, June 26, 2017 at 9:37:16 AM UTC-4, Eric Sosman wrote: >> It's true that dynamic insertions and deletions are simpler to >> write >> with an ArrayList than with a Thing[]. But your original post >> didn't mention simplicity as a goal; rather, you asked for "a more >> efficient way." >> >> Open-coded Thing[] will be no less efficient than ArrayList >> (barring silly mistakes in the open code), and stands a good chance of >> being more efficient. By how much remains an open question. > > Now if you're saying it would be more efficient to use String[] instead > of the ArrayList and int[] instead of the ArrayList, > the first question is how much more and do I end up copying all the code > from the ArrayList class when I need to remove or insert elements. The > second question is how do you manage an array of arrays. > > Consider list1 is actually ArrayList. Now list2 passes in the > integer list of indexes to return and a second parameter passes in a > second list of the element order to return. So each index now returns a > String[] set, all sets having the same number of elements, now you want > them sorted based on say their second element. > > The Oracle Java does this automatically in DefaultRowSorter.sort() but > it does take several seconds for each call with a relatively large table > as they completely rebuild arrays, while the filtering without sorting > appears instant. If I need an ordered list, and particularly if the list will be constructed once and read at least twice, I'll probably use a TreeMap. TreeMaps are implemented as red-black binary trees, so stepping through a one is generally fairly efficient and so are searches since they only need to look at one node in each level of the tree: a red-black tree with 4 million elements has 23 levels [1]. So far I haven't had any performance issues doing it this way, and I've used this approach for trees that big. However, it may be an inefficient approach for tiny trees due to the per-node overheads when adding or removing nodes. [1] Red-black binary trees are always balanced because they rebalance as nodes are added and are not sensitive to the order in which nodes are added. This is not the case for simple binary trees, which do not self- balance and in the extreme case, adding nodes in key sequence, will degenerate into an ordered linked list. -- martin@ | Martin Gregorie gregorie. | Essex, UK org |