/*
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.
*/
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.
This method returns the portion of TreeMap whose keys are less than
toKey.
Please note that, the SortedMap returned by this method is backed by
the original TreeMap. So any changes made to SortedMap will be
reflected back to original TreeMap.
*/
SortedMap sortedMap = treeMap.headMap("3");
System.out.println("Head Map Contains : " + sortedMap);
/*
Please also note that,
- SortedMap throws IllegalArgumentException for any attempts to insert the
key grater than or equal to toKey.
- subMap throws ClassCastException, if toKey can not be compared using
Map's Comparators
*/
}
}
/*
Output would be
Head Map Contains : {1=One, 2=Two}
*/
