your answer is one word "SortedSet"
The SortedSet interface extends Set and declares the behavior of a set sorted in ascending order. In addition to those methods defined by Set, the SortedSet interface declares the methods summarized in below Table:
Several methods throw a NoSuchElementException when no items are contained in the invoking set. A ClassCastException is thrown when an object is incompatible with the elements in a set.
A NullPointerException is thrown if an attempt is made to use a null object and null is not allowed in the set.
example : -
public class SortedSetTest {
public static void main(String[] args) {
// Create the sorted set
SortedSet set = new TreeSet();
// Add elements to the set
set.add("b");
set.add("c");
set.add("a");
// Iterating over the elements in the set
Iterator it = set.iterator();
while (it.hasNext()) {
// Get element
Object element = it.next();
System.out.println(element.toString());
}
}
}
source: http://www.tutorialspoint.com/java/java_sortedset_interface.htm
