How Does TreeMap Sort Data in Java?

How does TreeMap sort data in Java?

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<Integer, String> map = new TreeMap<>();
        map.put(3, "Three");
        map.put(1, "One");
        map.put(4, "Four");
        map.put(2, "Two");

        System.out.println(map);
    }
}

TreeMap in Java is a part of the Java Collections Framework and is used to store key-value pairs, sorted according to the natural ordering of the keys or by a specified comparator. Unlike HashMap, TreeMap maintains a sorted order, making it suitable for applications where the order of keys is important.

import java.util.TreeMap;
import java.util.Comparator;

public class CustomSortExample {
    public static void main(String[] args) {
        // Creating a TreeMap with a custom comparator
        TreeMap<String, Integer> map = new TreeMap<>(Comparator.reverseOrder());
        map.put("apple", 5);
        map.put("banana", 2);
        map.put("orange", 3);

        System.out.println(map); // Sorted in reverse order by key
    }
}

Causes

• TreeMap sorts elements based on keys using either their natural ordering or a custom comparator if provided during instantiation.
• By default, keys must be comparable, meaning they implement the Comparable interface.

Solutions

• To achieve natural ordering, ensure that the keys used in TreeMap implement Comparable, such as Integer, String, etc.
• For custom sorting, pass a Comparator to the TreeMap constructor, enabling control over the sorting criteria.

Mistake: Using a non-comparable key type

Solution: Ensure that your custom objects implement the Comparable interface or use a Comparator.

Mistake: Expecting insertion order to be maintained

Solution: Understand that TreeMap sorts keys and does not maintain the insertion order like LinkedHashMap.