With this example we are going to demonstrate how to obtain a head Map from a TreeMap. In short, to obtain a head Map from a TreeMap you should:
- Create a new TreeMap.
- Populate the map with elements, with
put(K key, V value)API method of TreeMap. - Invoke
headMap(K toKey)API method of TreeMap, with a specified key as parameter. It returns a SortedMap, that is a view of the portion of this map whose keys are strictly less than the specified key.
Let’s take a look at the code snippet that follows:
package com.javacodegeeks.snippets.core;
import java.util.SortedMap;
import java.util.TreeMap;
public class HeadmapTreeMap {
public static void main(String[] args) {
// Create a TreeMap and populate it with elements
TreeMap treeMap = new TreeMap();
treeMap.put("key_1","element_1");
treeMap.put("key_3","element_3");
treeMap.put("key_2","element_2");
treeMap.put("key_4","element_4");
treeMap.put("key_5","element_5");
/*
SortedMap headMap(Object toKey) returns the portion of TreeMap whose keys are less than toKey.
The SortedMap returned is backed by the original TreeMap. So any changes made to SortedMap will
be reflected back to original TreeMap.
*/
SortedMap headMap = treeMap.headMap("key_3");
System.out.println("headMap contains : " + headMap);
}
}
Output:
headMap contains : {key_1=element_1, key_2=element_2}
This was an example of how to obtain a head Map from a TreeMap in Java.
