The headSet() method of SortedSet interface in Java is used to return a view of the portion of this set whose elements are strictly less than the parameter toElement.
- The set returned by this method is backed by this set, so changes in the returned set are reflected in this set, and vice-versa.
- The set returned by this method supports all optional set operations that this set supports.
Note: The set returned by this method will throw an IllegalArgumentException if an attempt is made to insert an element outside its range.
Syntax:
SortedSet headSet(E toElement)
Where, E is the type of element maintained by this Set.
Parameters: This function accepts a single parameter toElement which represent the high endpoint (exclusive) of the returned set.
Return Value: It returns the last or the highest element currently in the set.
Exceptions:
- ClassCastException : It throws a ClassCastException if toElement is not compatible with this set’s comparator (or, if the set has no comparator, if toElement does not implement Comparable).
- NullPointerException : It throws a NullPointerException if the parameter toElement is null.
- IllegalArgumentException : It throws an IllegalArgumentException this set itself has a restricted range, and the parameter toElement lies outside the bounds of the range.
Below programs illustrate the above method:
Program 1:
// A Java program to demonstrate// working of SortedSetimport java.util.SortedSet;import java.util.TreeSet;  public class Main {    public static void main(String[] args)    {        // Create a TreeSet and inserting elements        SortedSet<Integer> s = new TreeSet<>();          // Adding Element to SortedSet        s.add(1);        s.add(5);        s.add(2);        s.add(3);        s.add(9);          // Returning the set with elements        // strictly less than the passed value        System.out.print("Elements strictly less than 7 in set are : "                         + s.headSet(7));    }} |
Output:
Elements strictly less than 7 in set are : [1, 2, 3, 5]
Program 2:
// A Java program to demonstrate// working of SortedSetimport java.util.SortedSet;import java.util.TreeSet;  public class Main {    public static void main(String[] args)    {        // Create a TreeSet and inserting elements        SortedSet<String> s = new TreeSet<>();          // Adding Element to SortedSet        s.add("Geeks");        s.add("For");        s.add("Geeks");        s.add("Code");        s.add("It");          // Returning the set with elements        // strictly less than the passed value        System.out.print("Element strictly less than Z in set is : "                         + s.headSet("Z"));    }} |
Output:
Element strictly less than Z in set is : [Code, For, Geeks, It]
Reference: https://docs.oracle.com/javase/10/docs/api/java/util/SortedSet.html#headSet(E)
