Returning an element from a TreeSet using binary search

Question

In TreeSet there is a method called contains that returns true if an element is in the set. I assume that this method uses binary search and does not iterate through all the elements in ascending order. Am I right?

I have a TreeSet that contains objects of a class that uses two String instance variables to distinguish it from other objects of the same class. I want to be able to create a method that searches the TreeSet by comparing the objects two instance variables (using get methods of course) with two other String variables and if they are equal, return the element. If the instance variables are less than go to the first element in the right subtree or if they are greater search in the left subtree etc. Is there a way to do this?

I know I could just store the objects in an ArrayList and use binary search to find the object, but this wouldn't be as fast as just searching the TreeSet.

Answer 1

set.tailSet(obj).first();

does what you want.

Answer 2

Rather than using a TreeSet, you could store your objects in a TreeMap<Foo, Foo> or TreeMap<FooKey, Foo> (if you can't easily create a new actual Foo each time you want to search). Sets are not really intended for lookup.

For the FooKey example, FooKey would be a simple immutable class that just contains the two Strings and is Comparable. Finding the value of Foo for two Strings would then be a simple matter of treeMap.get(new FooKey(firstString, secondString)). This does of course use the tree traversal you want to find the value.