In this article, we will discuss SortedMap interface with all its important methods in detail

1. Key points about SortedMap :

• SortedMap doesn’t allow duplicate keys
• Stores Key-Value pairs based on sorting-order
• Sorting-order could be either natural-ordering or customized-ordering

2. SortedMap interface :

• SortedMap interface is a sub-interface of Map interface (i.e.; SortedMap extends Map)
• To represent a group of key-value pairs as a single unit/entity, where duplicate keys aren’t allowed and keys are stored according to some sorting-order
• SortedMap allows only unique keys to be inserted
• SortedMap stores key-value pairs in sorting-order on the basis of keys only, not values
• SortedMap interface defines 6 specific methods in addition to inherited methods from Map interface
• Present in java.util package and extends java.util.Map interface

Source: Team BenchResources.Net

3. SortedMap interface methods :

4. Example to understand SortedMap specific method :

• SortedMap = [10-Alpha, 20-Beta, 30-Gamma, 40-delta, 50-epsilon, 60-lambda, 70-mu];
• firstKey() = 10
• lastKey() = 70
• headMap(40) =[10-Alpha, 20-Beta, 30-Gamma]
• tailMap(40) =[40-delta, 50-epsilon, 60-lambda, 70-mu]
• subMap(20, 70) =[20-Beta, 30-Gamma, 40-delta, 50-epsilon, 60-lambda]
• comparator() = null; as it uses default natural sorting order

5. SortedMap example :

SortedMapMethods.java

package in.bench.resources.java.collection;

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

public class SortedMapMethods {

	public static void main(String[] args) {

		// creating SortedMap reference and TreeMap object
		SortedMap<Integer, String> sm = new TreeMap<Integer, String>();

		// adding key-value pairs to SortedMap/TreeMap object
		sm.put(3, "Yahoo");
		sm.put(4, "Amazon");
		sm.put(7, "Twiter");
		sm.put(1, "Google");
		sm.put(5, "Reddit");
		sm.put(6, "LinkedIn");
		sm.put(2, "Facebook");

		System.out.println("Elements will be Sorted "
				+ "acc to Natural ordering:\n");
		System.out.println(sm);

		// SortedMap method operation
		System.out.println("\nFirst element of SortedMap : "
				+ sm.firstKey());
		System.out.println("\nLast element of SortedMap : "
				+ sm.lastKey());
		System.out.println("\nHead Map of 4th position : "
				+ sm.headMap(4));
		System.out.println("\nTail Map of 4th position : "
				+ sm.tailMap(4));
		System.out.println("\nSub Map between 2 &amp; 7 : "
				+ sm.subMap(2,7));
	}
}

Output:

Elements will be Sorted acc to Natural ordering:

{1=Google, 2=Facebook, 3=Yahoo, 4=Amazon, 5=Reddit, 6=LinkedIn, 7=Twiter}

First element of SortedMap : 1

Last element of SortedMap : 7

Head Map of 4th position : {1=Google, 2=Facebook, 3=Yahoo}

Tail Map of 4th position : {4=Amazon, 5=Reddit, 6=LinkedIn, 7=Twiter}

Sub Map between 2 & 7 : {2=Facebook, 3=Yahoo, 4=Amazon, 5=Reddit,
6=LinkedIn}

Note: All methods of SortedMap is non-synchronized

Q) How to make SortedMap synchronized ?

• It can be easily converted into synchronized SortedMap
• Using utility method synchronizedMap(sm); of java.util.Collections class
• Read Java – How to get synchronized version of Map ? for more details and examples

Map map = Collections.synchronizedMap(sm);

6. Class or interface that extends/implements SortedMap interface :

• NavigableMap interface extends SortedMap interface
• TreeMap class implements NavigableMap interface

7. Factors to consider while discussing any collection class :

We should consider below factors while discussing any implementation class of collection framework or for that matter Map interface,

• Underlying data structure
• Duplicates are allowed or Not
• Insertion order is maintained or Not
• Whether NULL insertion is possible or Not
• If possible, how many NULL values can be inserted
• Whether collection class provide sorting, by default
• Is there any way to apply customized sorting
• Performance, while dealing with retrieval or manipulation (addition/deletion)
• By default, all methods are synchronized or Not

Related Articles :

• Map interface
• Entry interface
• HashMap class
• LinkedHashMap class
• IdentityHashMap class
• WeakHashMap class
• SortedMap interface
• NavigableMap interface
• TreeMap class
• Hashtable class
• HashMap vs LinkedHashMap
• HashMap v/s LinkedHashMap v/s TreeMap
• HashMap v/s HashSet
• HashMap v/s Hashtable
• Properties class

References:

• https://docs.oracle.com/javase/tutorial/collections/intro/
• https://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html
• https://docs.oracle.com/javase/7/docs/api/java/util/Collection.html
• https://docs.oracle.com/javase/7/docs/api/java/util/Map.html
• https://docs.oracle.com/javase/7/docs/api/java/util/Map.Entry.html
• https://docs.oracle.com/javase/tutorial/collections/interfaces/map.html
• https://docs.oracle.com/javase/7/docs/api/java/util/SortedMap.html
• https://docs.oracle.com/javase/tutorial/collections/interfaces/sorted-map.html

Happy Coding !!
Happy Learning !!