Mastering Java 2026 – 400 Free Practice Questions to Pass the 'Thinking in Java' Exam

TreeSet is a collection in Java that does not allow duplicate elements to be stored. This is because it implements the Set interface, which does not allow duplicate elements. Option B is incorrect because while TreeSet does allow for rapid removals and insertions, this is not a defining characteristic of the collection. Option C is incorrect as TreeSet maintains elements in a sorted order, not a random order. Option D is incorrect because TreeSet is indeed based on the Set interface in Java.