The headSet() method of NavigableSet interface in Java is used to return a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement.
- The returned set is backed by this set, so changes in the returned set are reflected in this set, and vice-versa.
- The returned set supports all optional set operations that this set supports.
Note: The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.
Syntax:
NavigableSet<E> headSet(E toElement,
boolean inclusive)
Where, E is the type of elements maintained by this Set container.
Parameters: This function has two parameters :
- toElement – high endpoint of the returned set
- inclusive – true if the high endpoint is to be included in the returned view
Return Value: It return a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement.
Below programs illustrate the headSet() method in Java:
Program 1: NavigableSet with integer elements.
// A Java program to demonstrate// headSet() method of NavigableSet import java.util.NavigableSet;import java.util.TreeSet; public class GFG { public static void main(String[] args) { NavigableSet<Integer> ns = new TreeSet<>(); ns.add(0); ns.add(1); ns.add(2); ns.add(3); ns.add(4); ns.add(5); ns.add(6); System.out.println("Map with key-value less than "+ "given argument : " + ns.headSet(6)); System.out.println("Map with key-value less than or" + " equal to given argument : " + ns.headSet(6, true)); }} |
Map with key-value less than given argument : [0, 1, 2, 3, 4, 5] Map with key-value less than or equal to given argument : [0, 1, 2, 3, 4, 5, 6]
Program 2: NavigableSet with string elements.
// A Java program to demonstrate// headSet?() method of NavigableSet import java.util.NavigableSet;import java.util.TreeSet; public class GFG { public static void main(String[] args) { NavigableSet<String> ns = new TreeSet<>(); ns.add("A"); ns.add("B"); ns.add("C"); ns.add("D"); ns.add("E"); ns.add("F"); ns.add("G"); System.out.println("Map with key-value less than"+ " given argument : " + ns.headSet("F")); System.out.println("Map with key-value less than "+ "or equal to given argument : " + ns.headSet("F")); }} |
Map with key-value less than given argument : [A, B, C, D, E] Map with key-value less than or equal to given argument : [A, B, C, D, E]
Reference: https://docs.oracle.com/javase/10/docs/api/java/util/NavigableSet.html#headSet(E)