Get Head Map from Java TreeMap example

This Java Example shows how to get the portion of TreeMap whose keys are less than
the specified key using headMap method of Java TreeMap class.

public SortedMap headMap(Object toKey)

Returns a view of the portion of this map whose keys are strictly less than toKey. The returned sorted map is backed by this map, so changes in the returned sorted map are reflected in this map, and vice-versa. The returned sorted map supports all optional map operations.

The sorted map returned by this method will throw an IllegalArgumentException if the user attempts to insert a key greater than or equal to toKey.

See the example given below:

import java.util.SortedMap;
import java.util.TreeMap;

public class GetHeadMapFromTreeMapExample {

 public static void main(String[] args) {

  // create TreeMap object
  TreeMap treeMap = new TreeMap();

  // add key value pairs to TreeMap
  treeMap.put("1", "One");
  treeMap.put("3", "Three");
  treeMap.put("2", "Two");
  treeMap.put("5", "Five");
  treeMap.put("4", "Four");

  /*
   * To get a Head Map from Java TreeMap use,
   * SortedMap headMap(Object toKey) method
   * of Java TreeMap class.
   */

  SortedMap sortedMap = treeMap.headMap("3");

  System.out.println("Head Map Contains : " + sortedMap);

 }
}

The output is:


Head Map Contains : {1=One, 2=Two}