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Java Forum / General / January 2007What Collection to use?
Dear all, My app can load files using a FileChooser. I would like to store the last 4 loaded file pathes so I can use them later (ie fast access to last used files). I'm looking for the perfect Collection to store these 4 File objects. I think it should have the following properties 1. no duplicate objects 2. knowing the insert order (so you know which was last entered) 3. limited size (4 objects) and throwing out the oldest entry when inserting a new one (like a ring buffer maybe) Is there such a Collection already or do I have to homecook one? Thanks for your answers Phil PS: Is there a summary table on the web with all properties of the standard subclasses of Collection and Map? Not in the standard developer kid. point 3 is the hard one here. But there is a possibility you find the collection you need in the http:// jakarta.apache.org/commons/collections/ api. Maybe the FixedFileList will meet your expectations see the javadoc for more info http:// jakarta.apache.org/commons/collections/api-release/index.html > Dear all, > [quoted text clipped - 15 lines] > PS: Is there a summary table on the web with all properties of the > standard subclasses of Collection and Map? > Dear all, > [quoted text clipped - 9 lines] > > Is there such a Collection already or do I have to homecook one? #1 is a bit of a problem, because it excludes the closest collections. A LinkedHashSet iterates in the order of original insertion, so a re-load of the oldest file would not move it from being next to delete. I would probably get rid of that property, and use a LinkedList wrapped in a class that checks, every time it adds a new item, whether the size() is greater than four, and if so deletes the first item. Patricia I forgot: > 1. no duplicate objects > 2. knowing the insert order (so you know which was last entered) > 3. limited size (4 objects) and throwing out the oldest entry when > inserting a new one (like a ring buffer maybe) 4. when re-inserting an already present object, it should move to the front this makes LinkedHashSet not suitable :-( > I forgot: > [quoted text clipped - 6 lines] > > this makes LinkedHashSet not suitable :-( class MostRecentList implements Serializable { private final int maxSize; private final LinkedList<String> list = new LinkedList<String>(); public void add(String item) { if (list.contains(item)) { list.remove(item); } list.addFirst(item); while (list.size() > maxSize()) { list.removeLast(); } } } >> I forgot: >> [quoted text clipped - 19 lines] > } > } Wow! Thanks for that ready made solution! :-) Phil > class MostRecentList implements Serializable { > private final int maxSize; [quoted text clipped - 9 lines] > } > } Nice demo of why there is little need for this kind of functionality to be pre-packaged in the standard libraries. Minor nit: the above would be even shorter and sweeter if you deleted the if (list.contains(item)) test -- there is no need for it since an uncondition call to remove() would have the same effect. -- chris On Jan 30, 7:18 am, "Chris Uppal" <chris.up...@metagnostic.REMOVE- THIS.org> wrote: > > class MostRecentList implements Serializable { > > private final int maxSize; [quoted text clipped - 19 lines] > > -- chris Indeed. Actually, if I were creating this for real, I would implement a class MostRecentList<T> extend AbstractList<T>. Possibly using a fixed length object array as the backing store, or an ArrayList<T>. java.io.File[4]?  Signature======================================================================== Ian Pilcher arequipeno@gmail.com ======================================================================== >Dear all, > [quoted text clipped - 9 lines] > >Is there such a Collection already or do I have to homecook one? What you're describing is generally known as a Most Recently Used (MRU) list. I have an MRU class that uses a plain ol' ArrayList. I add the new one to the top of the list, then use indexOf() to check whether it's already in the list, and delete it from its old position if it is. Whether I delete one or not, if the list is now longer than 4 elements, delete one from from the bottom of the list. Lee Weiner lee AT leeweiner DOT org Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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