In this example we shall show you how to obtain a sub Map from a TreeMap. The TreeMap API provides methods for this operation. To obtain a sub Map from a TreeMap one should perform the following steps:
- Create a new TreeMap.
- Populate the map with elements, with
put(K key, V value)API method of TreeMap. - Invoke
subMap(Object fromKey, Object toKey)method of TreeMap. It returns a SortedMap containing elements fromfromKeytotoKey. The returned sub Map is backed by the original TreeMap, so any changes made to the sub map will also be reflected to the original TreeMap. In order to check if this is true we can remove an element from the sub map and check that it is removed from the original TreeMap also,
as described in the code snippet below.
package com.javacodegeeks.snippets.core;
import java.util.TreeMap;
import java.util.SortedMap;
public class SubMapTreeMap {
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");
/*
Use the SortedMap subMap(Object fromKey, Object toKey) operation
to get a sub Map of the original TreeMap. This method
returns an SortedMap object containing elements from fromKey
to toKey - 1 of the original TreeMap
*/
SortedMap sortedMap = treeMap.subMap("key_2","key_5");
System.out.println("SortedMap Contains : " + sortedMap);
/*
Sub Map returned is backed by original TreeMap. So any
changes made to sub map will also be reflected to the
original TreeMap. We will test that by removing an element
from the sub map and check that it is removed from the original
TreeMap also
*/
Object obj = sortedMap.remove("key_3");
System.out.println(obj + " is removed from sub map");
System.out.println("Elements in TreeMap : " + treeMap);
}
}
Output:
SortedMap Contains : {key_2=element_2, key_3=element_3, key_4=element_4}
element_3 is removed from sub map
Elements in TreeMap : {key_1=element_1, key_2=element_2, key_4=element_4, key_5=element_5}
This was an example of how to obtain a sub Map from a TreeMap in Java.
