Difference Between HashSet and TreeSet

What is TreeSet?

A TreeSet is another data structure used to store a collection of elements in computer science, particularly in languages like Java. It is part of the collections framework and is designed to store unique elements in sorted order.

Internally, a TreeSet is typically implemented using a self-balancing binary search tree, such as a red-black tree. This structure maintains the elements in sorted order, which allows for efficient retrieval of elements in sorted sequence. The elements are sorted based on their natural ordering (if they implement the Comparable interface) or by a specified comparator provided during construction.

TreeSetExample.java

• Java

Java

import java.util.TreeSet;   
public class TreeSetEx 
{   
public static void main(String[] args)   
{   
/* creating a TreeSet  */
TreeSet<String> treeSet= new TreeSet<String>();   
/* add elements to HashSet */  
treeSet.add("yellow");
treeSet.add("blue");
treeSet.add("green");
/* Duplicate elements will not be stored */
treeSet.add("blue");
 System.out.println("Elements in TreeSet are “);
System.out.println(treeSet);
}
}

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Output

Elements in TreeSet are
[blue, green,yellow]

Difference between Hashset and Treeset in Java

Now lets us see HashSet vs TreeSet. Here we will look at the differences between them.

Also read aboutt - Difference between HashMap and HashSet

Code

Let’s try to understand some of the differences through programs.

Null Values in HashSet

When you try to insert Null values in HashSet

• Java

Java

import java.util.HashSet;   
public class HashSetEx 
{   
public static void main(String[] args)   
{   
/* creating a HashSet  */
HashSet<Integer> hashSet= new HashSet<Integer>();   
/* add elements to HashSet   */
hashSet.add(5);
hashSet.add(2);
hashSet.add(3);
hashSet.add(6);
hashSet.add(0);
 System.out.println("Elements in HashSet are ");
/* iterate in hashSet */
for(int hash: hashSet){
System.out.println(hash);
}
}
}

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Output

Elements in HashSet are
0
2
3
5
6

Null Values in TreeSet

When you try to insert null values into TreeSet

• Java

Java

import java.util.TreeSet;   
public class TreeSetEx 
{   
public static void main(String[] args)   
{   
/* creating a TreeSet  */
TreeSet<String> treeSet= new TreeSet<String>();   
/* add elements to HashSet  */ 
treeSet.add("Mango");
treeSet.add("banana");
treeSet.add(null);
/* Duplicate elements will not be stored */
treeSet.add("blue");
 System.out.println("Elements in TreeSet are ");
 System.out.println(treeSet);
}
}

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Output

Comparison in HashSet

When you compare values in HashSet you will use the equals method.

• Java

Java

import java.util.HashSet;
public class Main
{
    public static void main(String[] args) {
    HashSet<Integer> h1= new HashSet<Integer>();
    /* add elememts */
    h1.add(1);
    h1.add(2);
    h1.add(5);
    h1.add(6);
    System.out.println("Elements in HashSet h1 are ");
/* iterate in hashSet */
for(int hash: h1){
System.out.println(hash +" ");
}
HashSet<Integer> h2= new HashSet<Integer>();
    /* add elememts */
    h2.add(1);
    h2.add(2);
    h2.add(5);
    h2.add(6);
    System.out.println("Elements in HashSet h2 are ");
for(int hash: h2){
System.out.println(hash +" ");
}
boolean value= h1.equals(h2);
System.out.println(value);
}
}

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Output

Elements in HashSet h1 are 
1 
2 
5 
6 
Elements in HashSet h2 are 
1 
2 
5 
6 
true

Comparison in TreeSet

Using the comparator method in TreeSet 

• Java

Java

import java.util.Comparator;
import java.util.TreeSet;

class MyComparison implements Comparator<String> {
  public int compare(String str1, String str2) {
    String a, b;

    a = str1;
    b = str2;

    return b.compareTo(a);
  }
  
}
public class Main
{
    public static void main(String[] args) {
     TreeSet<String> treeSet = new TreeSet<String>(new MyComparator());

    treeSet.add("blue");
    treeSet.add("orange");
    treeSet.add("green");
    treeSet.add("yellow");
    treeSet.add("purple");
    treeSet.add("Dark");

    for (String value : treeSet)
      System.out.print(value + " ");

    System.out.println();
    }
}

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Output

yellow purple orange green blue Dark

Similarities Between HashSet and TreeSet

• The Set interface is implemented by both classes
   
• They do not permit the use of duplicate values
   
• Thread safety is not provided by HashSet or TreeSet
   
• They are not synchronized, but we can synchronize them using the Collections.synchronizedSet() function
   
• Both classes' iterators are fail-fast in nature. If we try to edit an iterator after it has been generated, it throws a ConcurrentModificationException
   
• Both use the clone() function to produce a clone of their objects using the shallow copy technique

Which one is better to use?

HashSet offers O(1) performance for add, remove, and contains, but does not maintain order. TreeSet maintains elements in sorted order using a binary tree but has O(log n) worst-case performance for basic operations. Use HashSet if you need constant time performance and don't require order, and use TreeSet if you need sorted elements and efficient traversal in sorted order, especially for larger sets. The choice depends on specific use cases and set sizes.

Check out this problem - Duplicate Subtree In Binary Tree

Frequently Asked Questions

Which is better HashSet or TreeSet?

HashSet performs search, insert, and delete operations in constant time. This makes HashSet faster than TreeSet, which takes O(Log n) time. The reason behind this is that HashSet is implemented using a hash table, while TreeSet uses a sorted data structure.

What is the difference between HashSet and TreeSet?

HashSet is an unordered collection of unique elements, relying on hashing for fast operations. TreeSet is a sorted collection, using a self-balancing binary search tree.

Which is faster for searching operations TreeSet or HashSet?

HashSet offers faster search operations.

What is the difference between TreeSet and TreeMap?

TreeSet ensures elements are sorted, which aids in retrieval. TreeMap, like TreeSet, is sorted but stores key-value pairs.

Conclusion

In this blog, we have learned about the Difference Between HashSet and TreeSet. We started by introducing the sets and covered the differences between their sets. We have coded programs for a thorough understanding of HashSet vs TreeSet.

To learn more about Sets, please refer to our blog

Hashing 

Learn HashMaps 

String Hashing

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