AppletTalk.com Java discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Sorting an ArrayList twice...          AppletTalk.com Forum Index -> Java Help View previous topic :: View next topic   Author Message Frank Meyer Guest Posted: Wed May 25, 2005 7:29 pm    Post subject: Sorting an ArrayList twice... Hi newsgroup, I am a little swamped with my current Java problem and thought that maybe you can help me again: I have a ArrayList that contains Objects called rechteck who have a width and a height as int variables that can be read out with rechteck.getWidth() and rechteck.getHeight(). Now I have to sort this list (contains around 100 to 1000 elements) in a descending order firstly regarding the height and afterwards regarding the width if there are more than one object with the same height... What I found out in the Java Doc is that there is no easy solution to sort an ArrayList but nevertheless it is possible to sort an array. So I transformed the ArrayList to an Array by Object[] bOArray = bO.toArray(); whereas bO is my ArrayList. Besides the fact that this produces an array containing objects and not rechteck objects, it works fine, but I don't have any clue how to go on. I found that I can use Arrays.sort() for the first sort routine and the other Arrays.sort(intBegin,intEnd) for the second sort regarding the widths... but I don't understand the comparable request and the syntax I have to use... anything I coded just gives nearly every error that Java seems to have and I found no good tips within the net... So does anyone know how to sort my list? Or is there maybe even a better idea than using an array? I thought up some combinations of while and for loops together with a check if an element is bigger than the second a.s.o. but this seems to be a very difficult algorithm so I suggest that Java can support some more convenient ways... Any help is greatly appreciated! Thanks a lot in advance and best regards Frank Back to top Roland Guest Posted: Wed May 25, 2005 7:46 pm    Post subject: Re: Sorting an ArrayList twice... On 25-5-2005 21:29, Frank Meyer wrote: Quote: Hi newsgroup, I am a little swamped with my current Java problem and thought that maybe you can help me again: I have a ArrayList that contains Objects called rechteck who have a width and a height as int variables that can be read out with rechteck.getWidth() and rechteck.getHeight(). Now I have to sort this list (contains around 100 to 1000 elements) in a descending order firstly regarding the height and afterwards regarding the width if there are more than one object with the same height... What I found out in the Java Doc is that there is no easy solution to sort an ArrayList but nevertheless it is possible to sort an array. So I transformed the ArrayList to an Array by Object[] bOArray = bO.toArray(); whereas bO is my ArrayList. Besides the fact that this produces an array containing objects and not rechteck objects, it works fine, but I don't have any clue how to go on. I found that I can use Arrays.sort() for the first sort routine and the other Arrays.sort(intBegin,intEnd) for the second sort regarding the widths... but I don't understand the comparable request and the syntax I have to use... anything I coded just gives nearly every error that Java seems to have and I found no good tips within the net... So does anyone know how to sort my list? Or is there maybe even a better idea than using an array? I thought up some combinations of while and for loops together with a check if an element is bigger than the second a.s.o. but this seems to be a very difficult algorithm so I suggest that Java can support some more convenient ways... Any help is greatly appreciated! Thanks a lot in advance and best regards Frank Collections.sort(yourList, yourRechteckComparator); where Comparator yourRechteckComparator = new Comparator() { public int compare(Object o1, Object o2) { return compare( (Rechteck)o1, (Rechteck)o2); } public int compare(Rechteck r1, Rechteck r2) { int diff = r1.getHeight() - r2.getHeight(); if (diff == 0) { //:: height of both rectangles are equal // compare widths instead diff = r1.getWidth() - r2.getWidth(); } return diff; } }; [Untested, and assuming that elements in your list are of type Rechteck] <http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collections.html#sort(java.util.List,%20java.util.Comparator)> <http://java.sun.com/j2se/1.4.2/docs/api/java/util/Comparator.html#compare(java.lang.Object,%20java.lang.Object)> -- Regards, Roland de Ruiter ___ ___ /__/ w_/ /__/ / /_/ / Back to top Sebastian Scheid Guest Posted: Wed May 25, 2005 7:47 pm    Post subject: Re: Sorting an ArrayList twice... "Frank Meyer" <f.meyer (AT) 1und1 (DOT) de> schrieb im Newsbeitrag news:d72jls$vev$1 (AT) online (DOT) de... Quote: Hi newsgroup, I am a little swamped with my current Java problem and thought that maybe you can help me again: I have a ArrayList that contains Objects called rechteck who have a width and a height as int variables that can be read out with rechteck.getWidth() and rechteck.getHeight(). Now I have to sort this list (contains around 100 to 1000 elements) in a descending order firstly regarding the height and afterwards regarding the width if there are more than one object with the same height... What I found out in the Java Doc is that there is no easy solution to sort an ArrayList but nevertheless it is possible to sort an array. So I With Collections.sort() you can sort a List. You should let your class Rechteck implemente the interface Comparable (or you can give the sort() method an additional Comparator-object). Read the API doc for these interfaces. Regards Sebastian Back to top Frank Meyer Guest Posted: Wed May 25, 2005 8:00 pm    Post subject: Re: Sorting an ArrayList twice... Roland, Quote: [Code] [Untested, and assuming that elements in your list are of type Rechteck] thanks a lot... I've roughly checked it and it seems to work fine... I will try to understand it tomorrow ;o) Very best regards Frank Back to top Frank Meyer Guest Posted: Wed May 25, 2005 8:05 pm    Post subject: Re: Sorting an ArrayList twice... Sebastian, Quote: With Collections.sort() you can sort a List. You should let your class Rechteck implemente the interface Comparable (or you can give the sort() method an additional Comparator-object). Read the API doc for these interfaces. thanks for the help - I think it works now... 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