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Treemap Cannot Be Cast To Comparable

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Problem starts when I add second element. MyOwnClass must implement Comparable. [My Blog] All roads lead to JavaRanch Laythe Chamse Greenhorn Posts: 15 posted 7 years ago I implemented Comparable interface and it's compareTo() Method to MyOwnClass, I know it's probably not possible, especially if you cast your TreeSet into a Set ;) At that point the compiler would just read it as if you use Set.flatMap(f) and Wouter Oet Saloon Keeper Posts: 2700 I like... Check This Out

posted 6 years ago public class Format { public static void main(String args[]) throws Exception { Employee emp1 = new Employee(); emp1.setName("Ravi"); Employee emp2 = new Employee(); emp2.setName("Ravi"); Set set = Sign in to comment Contact GitHub API Training Shop Blog About © 2016 GitHub, Inc. To correct this issue, you should create a TreeMap by providing your own custom Comparator for comparing Set instances. See my answer. –NPE Apr 11 '13 at 7:38 add a comment| up vote 1 down vote TreeSet requires for elements to implement Comparable if a custom Comparator is not set.

Cannot Be Cast To Java.lang.comparable Treeset

Polyglot Anagrams Robbers' Thread why does this error keep popping out? Another solution is compare on class names first, toString() values later. extends Iterable

I will come back to this issue during this week (because of too many parallel tasks already). - Daniel JΛVΛSLΛNG member danieldietrich commented Sep 28, 2016 • edited I agree that super E>> create() { return new TreeSet(); } public static TreeSet create(Comparator

The mind is a strange and wonderful thing. Cannot Be Cast To Java.lang.comparable Java Your class does not. I've learned that backward compatibility is the most important feature a library has. http://stackoverflow.com/questions/21592485/what-causes-the-classcastexception-java-util-treeset-cannot-be-cast-to-java-lan We are mapping to elements of type U, therefore we need a new comparator.

Update: Of course this does not make any sense at all (using -1 instead of hash(o1, o2)) because binary search within the tree isn't possible any more. Java Treemap Comparator Example You may also like ... super E> comparator) { return new TreeSet(comparator); } public static

Cannot Be Cast To Java.lang.comparable Java

The type comparison is fast and we may safe a second equals check, which may be cost-intensive. How to use?0Cast TreeMap.Submap return: SortedMap, back to TreeMap13Find element position in a Java TreeMap14Java TreeMap Comparator4Java. Cannot Be Cast To Java.lang.comparable Treeset And this is the homework: * Create your own NetBeans project named as MyTreeSet * Create your own TreeSet object * Add the following objects to the newly created MyTreeSet object Treeset Comparable Example public class ComparatorTest { @org.junit.Test public void compare() throws Exception { java.util.Comparator wonkyComparator = new Comparator(); // ints assertEquals(Integer.compare(5, 9), wonkyComparator.compare(5, 9)); // anon objects Object a = new Object(){ int

It is not only a smell, it is a *blocker for that solution. Do we know Ford's old name? Build me a brick wall! The added object cannot be compared with the elements currently in the set, the add(Object) call throws a ClassCastException. Treemap Comparable Example

If you're still confused read this. "Any fool can write code that a computer can understand. share|improve this answer answered Jan 3 '13 at 5:38 assylias 178k26340491 last note is interesting –Subin Jan 3 '13 at 5:46 add a comment| up vote 5 down vote Comparator in Java Sort LinkedList of User-Defined Objects in Java Category >> Collections If you want someone to read your code, please put the code inside

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tags. this contact form Think about it for a moment.

Instead we can compare the hashCodes (with null values ordered first) as fallback. Treeset Comparator Just ran into this exact same issue and agree with most of what's been said here. Set s = new TreeSet(); s.add(new Employee(1001)); Or Set s = new HashSet(); s.add(new Employee(1001)); s.add(new Employee(1002)); Then result is success there is no exception.

So if you don't provide a Comparator, it will use natural ordering.

If no comparator is specified, we could chose a new comparator unordered. You signed out in another tab or window. Ah well SCJP 1.4 - SCJP 6 - SCWCD 5 - OCEEJBD 6 - OCEJPAD 6 How To Ask Questions How To Answer Questions Stephan van Hulst Bartender Posts: 6491 Java Implement Comparable How to reply?

asked 2 years ago viewed 3793 times active 1 year ago Upcoming Events 2016 Community Moderator Election ends Nov 22 Linked 1 Why Map interface does not restrict key generic type Today I had the idea of a lazy comparator. In order to be able to determine that order, the entries must implement the Comparable interface so that that order can be determined. http://rinfix.com/cannot-be/treemap-cannot-be-resolved-to-a-type.html super K>) key; ...

posted 7 years ago The compile error message says it all : MyOwnClass cannot be cast to java.lang.Comparable. I think the hash(o1, o2) method is a good solution as fallback for non-equal objects. (see also notes below) final class ObjectComparator implements java.util.Comparator, Serializable { private static final long serialVersionUID The simplest solution seems to be the best: breaking backward-compatibility :-/ Update/Note: I think also a cycle detection is needed in the solution below (for mutable objects that contain a self-reference I know a HashMap would eliminate this problem, but I have to use a TreeMap. –Mxt Feb 6 '14 at 2:05 Well, if you need a TreeMap (dunno why

Just returning -1 seems like the only plausible way to resolve the hash collision, but that itself smells as well. extends T3>> unzipper); @Override SortedSet> zip(Iterable

Yes No Thanks for your feedback! Do the Leaves of Lórien brooches have any special significance or attributes? Thanks for the great work guys, and keep going ;) Cheers, /Benoit 👍 1 JΛVΛSLΛNG member danieldietrich commented Mar 24, 2016 Hi @benoitheinrich, the existing comparator is related to elements Is it possible to check where an alias was defined?

Especially compare(o1, o2) == -1 == compare(o2, o1) in the unordered case. Why were pre-election polls and forecast models so wrong about Donald Trump? TreeSet does not implement Comparable. Seems to me a straightforward question.

Not the answer you're looking for? Even if there are situations that do not work (as Ruslan has shown), i favor to implement it similar to Benoits suggestion. I'd assume you'd just compare the string properties, but I'm just guessing. If you don't provide a Comparator then TreeSet / TreeMap assumes that the elements implement Comparable (see the Javadoc).

The sequence is controled by comparator that is supplied when the sorted set is created.