NavigableSet headSet() method in Java
Last Updated :
29 Sep, 2018
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.
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 ));
}
}
|
Output:
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.
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" ));
}
}
|
Output:
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)
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