Difference between HashSet vs TreeSet in Java, Best Tutorial of HashSet vs TreeSet 2024

HashSet vs TreeSet: Java provides several collection classes to manage groups of objects efficiently. Two commonly used classes for managing sets of elements are HashSet and TreeSet.

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HashSet vs TreeSet in Java

HashSet

HashSet is a collection class in Java that implements the Set interface. It uses a hash table to store elements and does not allow duplicate values. HashSet does not guarantee the order of elements.

HashSet: Unordered and Unique

The HashSet class is like a magical bag where you can throw in items, and it ensures that you don’t have duplicates. However, the order in which you put things into the bag doesn’t guarantee the order in which you’ll take them out. Let’s look at a simple example:

HashSet Example:

import java.util.HashSet;

public class HashSetExample {
    public static void main(String[] args) {
        // Creating a HashSet
        HashSet hashSet = new HashSet<>();

        // Adding elements to the HashSet
        hashSet.add("Apple");
        hashSet.add("Banana");
        hashSet.add("Orange");
        hashSet.add("Grapes");
        hashSet.add("Apple"); // Duplicate elements are not allowed

        // Displaying the elements of HashSet
        System.out.println("HashSet: " + hashSet);
    }
}

In this example, a HashSet is created to store strings. The HashSet does not allow duplicate elements, so when trying to add “Apple” again, it will not be added.

TreeSet

TreeSet is another collection class in Java that implements the Set interface. It stores elements in a sorted order (ascending by default) using a red-black tree. TreeSet does not allow duplicate elements.

TreeSet: Sorted and Unique

On the other hand, TreeSet is like a neatly organized shelf where items are not unique but also arranged in a specific order. This order is determined by the natural ordering of the elements or by a specified comparator. Let’s see how it works:

TreeSet Example:

import java.util.TreeSet;

public class TreeSetExample {
    public static void main(String[] args) {
        // Creating a TreeSet
        TreeSet treeSet = new TreeSet<>();

        // Adding elements to the TreeSet
        treeSet.add("Apple");
        treeSet.add("Banana");
        treeSet.add("Orange");
        treeSet.add("Grapes");
        treeSet.add("Apple"); // Duplicate elements are not allowed

        // Displaying the elements of TreeSet (naturally ordered)
        System.out.println("TreeSet (Ordered): " + treeSet);

        // Displaying the elements of TreeSet in reverse order
        System.out.println("TreeSet (Reverse Ordered): " + treeSet.descendingSet());
    }
}

In this example, a TreeSet is created to store strings. TreeSet is automatically ordered, so the elements will be displayed in their natural order. Additionally, we used descendingSet() to display the elements in reverse order.