java.util.TreeSet.headSet() Method

Description

The headSet(E toElement) method is used to return a view of the portion of this set whose elements are strictly less than toElement(input).The returned set is backed by this set, so changes in the returned set are reflected in this set, and vice-versa.

Declaration

Following is the declaration for java.util.TreeSet.headSet() method.

public SortedSet<E> headSet(E toElement)

Parameters

toElement − This is the high endpoint (exclusive) of the returned set.

Return Value

The method call returns a view of the portion of this set whose elements are strictly less than toElement.

Exception

• ClassCastException − This exception is thrown if 'toElement' cannot be compared to elements currently in the set.

• NullPointerException − This exception is thrown if 'toElement' is null and this set uses natural ordering, or its comparator does not permit null elements.

• IllegalArgumentException − This exception is thrown if this set itself has a restricted range, and 'toElement' lies outside the bounds of the range.

Example

The following example shows the usage of java.util.TreeSet.headSet() method.

package com.tutorialspoint;

import java.util.Iterator;
import java.util.TreeSet;

public class TreeSetDemo {
   public static void main(String[] args) {

      // creating TreeSet 
      TreeSet <Integer>tree = new TreeSet<Integer>();
      TreeSet <Integer>treeheadset = new TreeSet<Integer>();

      // adding in the tree
      tree.add(12);
      tree.add(13);
      tree.add(14);
      tree.add(15);
      tree.add(16);
      tree.add(17);

      // getting values less than 15
      treeheadset = (TreeSet)tree.headSet(15);  
    
      // creating iterator
      Iterator iterator;
      iterator = treeheadset.iterator();

      //Displaying the tree set data
      System.out.println("Tree set data: ");     
      
      while (iterator.hasNext()) {
         System.out.println(iterator.next() + " ");
      }
   }    
}

Let us compile and run the above program, this will produce the following result.

Tree set data: 
12 
13 
14 

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