Java TreeMap subMap() Method

The TreeMap.subMap() method in Java allows you to retrieve a view of a portion of a TreeMap based on a range of keys. This guide will cover the method’s usage, explain how it works, and provide examples to demonstrate its functionality. We will also cover a real-world use case to show how TreeMap.subMap() can be used effectively.

Table of Contents

1. Introduction
2. subMap Method Syntax
   • NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)
   • SortedMap<K,V> subMap(K fromKey, K toKey)
3. Examples
   • Using NavigableMap.subMap()
   • Using SortedMap.subMap()
4. Real-World Use Case
   • Example: Retrieving a Subset of Contacts
5. Conclusion

Introduction

The TreeMap.subMap() method is a member of the TreeMap class in Java. It provides a way to obtain a view of a specific portion of the map based on key ranges. This method can be used to create a subset of the map with keys that fall within a specified range.

subMap() Method Syntax

NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)

This method returns a view of the portion of this map whose keys range from fromKey to toKey.

Syntax

public NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)

• Parameters:
  • fromKey: The low endpoint of the keys in the returned map.
  • fromInclusive: true if the low endpoint is to be included in the returned view.
  • toKey: The high endpoint of the keys in the returned map.
  • toInclusive: true if the high endpoint is to be included in the returned view.
• Returns: A NavigableMap view of the specified portion of this map.

SortedMap<K,V> subMap(K fromKey, K toKey)

This method returns a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive.

Syntax

public SortedMap<K,V> subMap(K fromKey, K toKey)

• Parameters:
  • fromKey: The low endpoint (inclusive) of the keys in the returned map.
  • toKey: The high endpoint (exclusive) of the keys in the returned map.
• Returns: A SortedMap view of the specified portion of this map.

Examples

Using NavigableMap.subMap()

Example

import java.util.TreeMap;
import java.util.NavigableMap;

public class NavigableMapSubMapExample {
    public static void main(String[] args) {
        // Creating a TreeMap with String keys and Integer values
        TreeMap<String, Integer> treeMap = new TreeMap<>();

        // Adding entries to the TreeMap
        treeMap.put("Ravi", 25);
        treeMap.put("Priya", 30);
        treeMap.put("Vijay", 35);
        treeMap.put("Anita", 28);
        treeMap.put("Suresh", 40);

        // Getting a submap from "Priya" (inclusive) to "Vijay" (inclusive)
        NavigableMap<String, Integer> subMap = treeMap.subMap("Priya", true, "Vijay", true);

        // Printing the submap
        System.out.println("SubMap from 'Priya' to 'Vijay': " + subMap);
    }
}

Output:

SubMap from 'Priya' to 'Vijay': {Priya=30, Ravi=25, Vijay=35}

Using SortedMap.subMap()

Example

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

public class SortedMapSubMapExample {
    public static void main(String[] args) {
        // Creating a TreeMap with String keys and Integer values
        TreeMap<String, Integer> treeMap = new TreeMap<>();

        // Adding entries to the TreeMap
        treeMap.put("Ravi", 25);
        treeMap.put("Priya", 30);
        treeMap.put("Vijay", 35);
        treeMap.put("Anita", 28);
        treeMap.put("Suresh", 40);

        // Getting a submap from "Priya" (inclusive) to "Vijay" (exclusive)
        SortedMap<String, Integer> subMap = treeMap.subMap("Priya", "Vijay");

        // Printing the submap
        System.out.println("SubMap from 'Priya' to 'Vijay' (exclusive): " + subMap);
    }
}

Output:

SubMap from 'Priya' to 'Vijay' (exclusive): {Priya=30, Ravi=25}

Real-World Use Case

Example: Retrieving a Subset of Contacts

A common real-world use case for TreeMap.subMap() is managing a contact list where you need to retrieve a subset of contacts based on their names.

Example

import java.util.TreeMap;
import java.util.NavigableMap;

public class ContactManager {
    public static void main(String[] args) {
        // Creating a TreeMap to manage contacts
        TreeMap<String, Integer> contacts = new TreeMap<>();

        // Adding contacts to the TreeMap
        contacts.put("Ravi", 1234567890);
        contacts.put("Priya", 9876543210);
        contacts.put("Vijay", 5556667777);
        contacts.put("Anita", 4445556666);
        contacts.put("Suresh", 6667778888);

        // Retrieving a subset of contacts from "Priya" (inclusive) to "Vijay" (inclusive)
        NavigableMap<String, Integer> subContacts = contacts.subMap("Priya", true, "Vijay", true);

        // Printing the subset of contacts
        System.out.println("Subset of contacts from 'Priya' to 'Vijay': ");
        for (Map.Entry<String, Integer> entry : subContacts.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

Output:

Subset of contacts from 'Priya' to 'Vijay':
Priya: 9876543210
Ravi: 1234567890
Vijay: 5556667777

In this example, TreeMap.subMap() is used to retrieve a subset of contacts based on their names, making it easy to manage and view a specific portion of the contact list.

Conclusion

The TreeMap.subMap() method in Java provides a way to obtain a view of a portion of the map based on key ranges. By understanding how to use this method, you can efficiently manage collections of key-value pairs in your Java applications. The method allows you to create subsets of the map, making it a versatile tool for data management in various scenarios.