Java Collections Framework - The SortedMap Interface

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In this guide, we will learn about SortedMap interface, SortedMap interface methods and SortedMap interface implementation class.

Overview of SortedMap Interface

A SortedMap is a Map that maintains its entries in ascending order, sorted according to the keys natural ordering, or according to a Comparator provided at the time of the SortedMap creation.

The SortedMap interface provides operations for normal Map operations and for the following:

• Range view — performs arbitrary range operations on the sorted map
• Endpoints — returns the first or the last key in the sorted map
• Comparator access — returns the Comparator, if any, used to sort the map

The following interface is the Map analog of SortedSet.

public interface SortedMap<K, V> extends Map<K, V>{ Comparator<? super K> comparator(); SortedMap<K, V> subMap(K fromKey, K toKey); SortedMap<K, V> headMap(K toKey); SortedMap<K, V> tailMap(K fromKey); K firstKey(); K lastKey(); }

SortedMap Interface with It's TreeSet Implementation Class Example

This example demonstrates the few API of SortedMap Interface using TreeSet implementation class.

• firstKey()
• lastKey()
• tailMap(String fromKey)
• .headMap(String toKey)

import java.util.SortedMap; import java.util.TreeMap; public class CreateTreeMapExample { public static void main(String[] args) { // Creating a TreeMap SortedMap<String, String> fileExtensions = new TreeMap<>(); // Adding new key-value pairs to a TreeMap fileExtensions.put("python", ".py"); fileExtensions.put("c++", ".cpp"); fileExtensions.put("kotlin", ".kt"); fileExtensions.put("golang", ".go"); fileExtensions.put("java", ".java"); // Printing the TreeMap (Output will be sorted based on keys) System.out.println(fileExtensions); System.out.println("First Kay :" + fileExtensions.firstKey()); System.out.println("Last Kay :" + fileExtensions.lastKey()); SortedMap<String, String> sortedMap = fileExtensions.tailMap("java"); System.out.println("tailMap : " + sortedMap); sortedMap = fileExtensions.headMap("java"); System.out.println("headMap : " + sortedMap); } }

Output:

{c++=.cpp, golang=.go, java=.java, kotlin=.kt, python=.py} First Kay :c++ Last Kay :python tailMap : {java=.java, kotlin=.kt, python=.py} headMap : {c++=.cpp, golang=.go}

SortedMap Interface Hierarchy Diagram

SortedMap Interface APIs/Methods

SortedMap Interface Implementations

• TreeMap Class

Related Collections Framework Interfaces

• Collections Framework - The Collection Interface
• Collections Framework - The Set Interface
• Collections Framework - The SortedSet Interface
• Collections Framework - The List Interface
• Collections Framework - The Queue Interface
• Collections Framework - The Deque Interface
• Collections Framework - The Map Interface
• Collections Framework - The SortedMap Interface