It is in the javadoc for Comparator "Caution should be exercised when using a comparator capable of imposing an ordering inconsistent with equals to order a sorted set (or sorted map). Suppose a sorted set (or sorted map) with an explicit comparator c is used with elements (or keys) drawn from a set S. If the ordering imposed by c on S is inconsistent with equals, the sorted set (or sorted map) will behave "strangely." In particular the sorted set (or sorted map) will violate the general contract for set (or map), which is defined in terms of equals."
http://java.sun.com/javase/6/docs/api/java/util/Comparator.html On Thu, Mar 5, 2009 at 1:50 PM, Johan Compagner <jcompag...@gmail.com>wrote: > For example. > > You want a tree set with a case insensitive comparator.. Because you want > to > order case insensitive.. > That breaks the equals contract. > > So that "note" in the doc just makes the TreeSet completely worthless > > johan > > > On Thu, Mar 5, 2009 at 13:46, Johan Compagner <jcompag...@gmail.com> > wrote: > > > that is then the wrong spec that i talk about > > That is completely stupid > > > > With a comparator you just OVERRIDE the equals, thats the whole point! > > > > johan > > > > > > > > On Thu, Mar 5, 2009 at 13:44, Pointbreak > > <pointbreak+wicketst...@ml1.net<pointbreak%2bwicketst...@ml1.net> > <pointbreak%2bwicketst...@ml1.net <pointbreak%252bwicketst...@ml1.net>> > > > wrote: > > > >> Sorry, I have to correct myself. According to the API-docs, the compare > >> method in a TreeSet must be consistent with equals. In Johan's example > >> it is not. > >> > >> On Thu, 05 Mar 2009 13:36 +0100, "Pointbreak" > >> <pointbreak+wicketst...@ml1.net <pointbreak%2bwicketst...@ml1.net> < > pointbreak%2bwicketst...@ml1.net <pointbreak%252bwicketst...@ml1.net>>> > >> wrote: > >> > You are missing the point. With a string it will work, because the > >> > elements will actually be the same string objects, so the > String.equals > >> > and the overridden compare method will give the same results in the > >> > example. Johan's point is that while set1.removeAll() is called, it is > >> > not the compare method of set1 that is used, which seems > >> > counterintuitive. > >> > > >> > On Thu, 05 Mar 2009 13:13 +0100, "Dave Schoorl" < > mailli...@cyber-d.com> > >> > wrote: > >> > > If I change every MyObject in a String, everything is fine. Perhaps > >> the > >> > > MyObject is not obeying the necessary contracts? > >> > > > >> > > See adjusted code below: > >> > > > >> > > > >> > > > >> > > import java.util.ArrayList; > >> > > import java.util.Collection; > >> > > import java.util.Comparator; > >> > > import java.util.HashSet; > >> > > import java.util.Iterator; > >> > > import java.util.TreeSet; > >> > > > >> > > public class TestWithStrings > >> > > { > >> > > public static void main(String[] args) > >> > > { > >> > > TreeSet<String> set1 = getCleanSet(); > >> > > > >> > > HashSet<String> set2 = new HashSet<String>(); > >> > > set2.add("johan"); > >> > > > >> > > > >> > > set1.removeAll(set2); > >> > > > >> > > System.err.println("this works: " + set1.size() + " == 1, > and > >> > > remaining object is " + set1.iterator().next() + " == rob"); > >> > > > >> > > // add removed back in > >> > > set1 = getCleanSet(); > >> > > > >> > > // increase the size of set2 with some other random others > >> > > set2.add("random1"); > >> > > set2.add("random2"); > >> > > > >> > > // now size is bigger then set1, call removeall again: > >> > > set1.removeAll(set2); > >> > > > >> > > System.err.println("this doesnt work: " + set1.size() + " != > >> 1, > >> > > so now both objects stil remain! This is because " + > >> > > "removeAll isnt overwritten by TreeSet and > AbstractSet > >> > > walks over the smallest set but then compare fails"); > >> > > > >> > > // same for retainAll that also compares wrong. > >> > > set1 = getCleanSet(); > >> > > set1.retainAll(set2); > >> > > > >> > > System.err.println("set1 is now completely empty, but it > >> should > >> > > have 1 left: " + set1); > >> > > > >> > > // so both methods should always iterator through the > >> colleciton > >> > > they get and do the compare on its self > >> > > > >> > > set1 = getCleanFixedSet(); > >> > > > >> > > set1.removeAll(set2); > >> > > > >> > > System.err.println("now this works: " + set1.size() + " == > 1, > >> > > and remainng object is " + set1.iterator().next() + " == rob"); > >> > > > >> > > // add removed back in > >> > > set1 = getCleanFixedSet(); > >> > > > >> > > set1.retainAll(set2); > >> > > > >> > > System.err.println("set1 is now correct, it has 1 left: " + > >> > > set1); > >> > > > >> > > } > >> > > > >> > > public static TreeSet<String> getCleanSet() { > >> > > TreeSet<String> set1 = new TreeSet<String>(new > >> > > Comparator<String>(){ > >> > > > >> > > public int compare(String o1, String o2) > >> > > { > >> > > return o1.compareToIgnoreCase(o2); > >> > > } > >> > > }); > >> > > > >> > > set1.add("johan"); > >> > > set1.add("rob"); > >> > > > >> > > return set1; > >> > > } > >> > > > >> > > public static TreeSet<String> getCleanFixedSet() { > >> > > TreeSet<String> set1 = new MyFixedTreeSet<String>(new > >> > > Comparator<String>(){ > >> > > > >> > > public int compare(String o1, String o2) > >> > > { > >> > > return o1.compareToIgnoreCase(o2); > >> > > } > >> > > }); > >> > > > >> > > set1.add("johan"); > >> > > set1.add("rob"); > >> > > return set1; > >> > > } > >> > > > >> > > public static class MyFixedTreeSet<E> extends TreeSet<E> > >> > > { > >> > > public MyFixedTreeSet(Comparator<? super E> comparator) > >> > > { > >> > > super(comparator); > >> > > } > >> > > > >> > > @Override > >> > > public boolean retainAll(Collection<?> c) > >> > > { > >> > > ArrayList<E> list = new ArrayList<E>(); > >> > > Iterator<?> e = c.iterator(); > >> > > while (e.hasNext()) { > >> > > Object next = e.next(); > >> > > if (contains(next)) { > >> > > list.add((E)next); > >> > > } > >> > > } > >> > > boolean modified = list.size() < size(); > >> > > if (modified) > >> > > { > >> > > clear(); > >> > > for (E item : list) > >> > > { > >> > > add(item); > >> > > } > >> > > } > >> > > return modified; > >> > > } > >> > > > >> > > @Override > >> > > public boolean removeAll(Collection<?> c) > >> > > { > >> > > boolean modified = false; > >> > > for (Iterator<?> i = c.iterator(); i.hasNext(); ) > >> > > modified |= remove(i.next()); > >> > > return modified; > >> > > } > >> > > } > >> > > } > >> > > > >> > > > >> > > > >> > > > --------------------------------------------------------------------- > >> > > To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org > >> > > For additional commands, e-mail: users-h...@wicket.apache.org > >> > > > >> > > >> > --------------------------------------------------------------------- > >> > To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org > >> > For additional commands, e-mail: users-h...@wicket.apache.org > >> > > >> > >> --------------------------------------------------------------------- > >> To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org > >> For additional commands, e-mail: users-h...@wicket.apache.org > >> > >> > > >
