treeset

I posted some code here which correctly solved a problem the poster had. OP wanted to remove duplicates and bring certain special items to the top of a list. I used a TreeSet with a special Comparable class which wrapped the Locale they were working with to achieve what they wanted. I then got to thinking ... as you do ... that I was eliminating duplicates by returning 0 from the compareTo method, not by returning true from an equals implementation as one would need to do to correctly indicate a duplicate in a Set (from the definition of a Set ). I have no objection to using this technique but

Here is the piece of code that I have used for Java 5.0 TreeSet<Integer> treeSetObj = new TreeSet<Integer>( Collections.reverseOrder() ) ; Collections.reverseOrder() is used to obtain a comparator in order to reverse the way the elements are stored and iterated. Is there a more optimized way of doing it? Why do you think this approach won't be optimized? The reverse order Comparator is simply going to be flipping the sign of the output from the actual Comparator (or output from compareTo on the Comparable objects being inserted) and I would therefore imagine it is very fast. An alternative

I'm using a TreeSet<Integer> and I'd quite simply like to find the index of a number in the set. Is there a nice way to do this that actually makes use of the O(log(n)) complexity of binary trees? (If not, what should I do, and does anyone know why not? I'm curious why such a class would be included in Java without something like a search function.) As @Yrlec points out set.headSet(element).size will returns 0 though there is no this element in the set. So we'd better check: return set.contains(element)? set.headSet(element).size(): -1; Here is a test case to show the problem: public static

I've got a object that defines a 'natural sort order' using Comparable<>. These are being stored in TreeSets. Other than removing and re-adding the object, is there another way to update the sort when the members that are used to define the sort order are updated? As others have noted, there is no in-built way. But you can always subclass that TreeSet, with your constructor(s) of choice, and add in the required functionality: public class UpdateableTreeSet<T extends Updateable> extends TreeSet<T> { // definition of updateable interface Updateable{ void update(Object value); } // constructors

I have several arrays in the form: private static String[] patientNames = { "John Lennon", "Paul McCartney", "George Harrison", "Ringo Starr" }; Then I make a TreeSet like this: TreeSet<Patient> patTreeSet = new TreeSet<Patient>(); Where Patient is a different class that makes "Patient" objects. Then I loop through each element in my arrays to create several patients and add them to my patTreeSet like this: for(int i = 0; i< patientNames.length; i++){ Date dob = date.getDate("MM/dd/yyyy", patientBirthDates[i]); Patient p = new PatientImpl(patientNames[i], patientSSN[i], dob); patTreeSet.add(p)

I have a quick question about TreeSet collections and hashCode methods. I have a TreeSet and I'm adding objects to it, before I add an object, I check to see if it exists in the TreeSet using the contains method. I have 2 distinct objects, each of which produce a distinct hashCode using my implementation of the hashCode method, example below: public int hashCode() { int hash = 7; hash = hash * 31 + anAttribute.hashCode(); hash = hash * 31 + anotherAttribute.hashCode(); hash = hash * 31 + yetAnotherAttribute.hashCode(); return hash; } The hashCodes for a particular run are: 76126352 and