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Byron is a master software engineer working in the IT and Telecom domains. He is an applications developer in a wide variety of applications/services. He is currently acting as the team leader and technical architect for a proprietary service creation and integration platform for both the IT and Telecom industries in addition to a in-house big data real-time analytics solution. He is always fascinated by SOA, middleware services and mobile development. Byron is co-founder and Executive Editor at Java Code Geeks.

Obtain sub Map from TreeMap example

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 from fromKey to toKey. 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.

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