NavigableSet represents a navigable set in Java Collection Framework. The NavigableSet interface inherits from the SortedSet interface. It behaves like a SortedSet with the exception that we have navigation methods available in addition to the sorting mechanisms of the SortedSet. NavigableSet interface can navigate the set in reverse order compared to the order defined in SortedSet. A NavigableSet may be accessed and traversed in either ascending or descending order. The classes that implement this interface are, TreeSet and ConcurrentSkipListSet.
In Java, we must import the java.util.NavigableSet package to use NavigableSet. Once we import the package, here's how we can create navigable sets.
// NavigableSet implementation by TreeSet class
NavigableSet<String> numbers = new TreeSet<>();
The NavigableSet provides various methods that can be used to navigate over its elements.
| Method Name | Description |
|---|---|
| descendingSet() | reverses the order of elements in a set. |
| descendingIterator() | returns an iterator that can be used to iterate over a set in reverse order. |
| ceiling() | returns the lowest element among those elements that are greater than or equal to the specified element. |
| floor() | returns the greatest element among those elements that are less than or equal to the specified element. |
| higher() | returns the lowest element among those elements that are greater than the specified element. |
| lower() | returns the greatest element among those elements that are less than the specified element. |
| pollFirst() | returns and removes the first element from the set. |
| pollLast() | returns and removes the last element from the set. |
import java.util.NavigableSet;
import java.util.TreeSet;
public class NavigableSetExample {
public static void main(String[] args) {
// Creating NavigableSet using the TreeSet
NavigableSet<Integer> numbers = new TreeSet<>();
// Insert elements to the set
numbers.add(1);
numbers.add(2);
numbers.add(3);
System.out.println("NavigableSet: " + numbers);
// Access the first element
int firstElement = numbers.first();
System.out.println("First Number: " + firstElement);
// Access the last element
int lastElement = numbers.last();
System.out.println("Last Element: " + lastElement);
// Remove the first element
int number1 = numbers.pollFirst();
System.out.println("Removed First Element: " + number1);
// Remove the last element
int number2 = numbers.pollLast();
System.out.println("Removed Last Element: " + number2);
}
}