Difference between List and Set in Java

Last Updated on August 3, 2023 by Mayank Dham

When working with collections in Java, it is critical to select the appropriate data structure based on your application’s needs. List and Set are two popular collection interfaces in Java. While they share similarities, there are fundamental differences between them. In this article, we will look at the differences between List and Set to help you make an informed decision when choosing a collection type for your Java programs.

Overview of List

A list is an ordered collection with elements that can be duplicated. It maintains element insertion order and provides positional access to them.
Characteristics of a List in Java:
The key characteristics of a list are:

1. Elements can be added or removed at any position.
2. Elements can be accessed by their index.
3. Allows duplicate elements.
4. Provides methods for manipulating the list, such as adding, removing, and modifying elements.

Implementation of a List in Java

Here’s an example of a list in Java

import java.util.*;    
class ListExample{    
    public static void main(String args[]){    

    List names = new ArrayList();    

    names.add("Emma");    
    names.add("Adele");    
    names.add("Aria");    
    names.add("Ally");    

    for(String name: names)    
        System.out.println(name);    
    }    
}   

Output

Overview of Set

A set is an unordered collection with no duplicate elements. It guarantees that each element in the Set is distinct.
Characteristics of Set in Java:
The key characteristics of Set are:

1. It does not maintain the insertion order of elements.
2. It does not provide positional access to elements.
3. It does not allow duplicate elements.
4. Provides methods for adding and removing elements, as well as checking for element existence.

Implementation of a Set in Java

Here’s an example of a list in Java

import java.util.*;     
public class SetExample{     
    public static void main(String[] args)     
    {     
        Set veg = new HashSet();     
        veg.add("Ginger");     
        veg.add("Garlic");     
        veg.add("Onion");     
        veg.add("Ginger");     

        System.out.println(veg);     
    }     
}    

Output

Difference Between List and Set in Java

Here are some of the key difference between list and set in Java

S.No	List	Set
1.	The list implementation allows us to add the same or duplicate elements.	The set implementation doesn’t allow us to add the same or duplicate elements.
2.	The insertion order is maintained by the List.	It doesn’t maintain the insertion order of elements.
3.	List allows us to add any number of null values.	Set allows us to add at least one null value to it.
4.	The List implementation classes are LinkedList and ArrayList.	The Set implementation classes are TreeSet, HashSet, and LinkedHashSet.
5.	We can get the element of a specified index from the list using the get() method.	We cannot find the element from the Set based on the index because it doesn’t provide any get method().
6.	It is used when we want to frequently access the elements by using the index.	It is used when we want to design a collection of distinct elements.
7.	The method listiterator() of the List interface is used to iterate the List elements.	The iterator is used when we need to iterate over the Set elements.

Choosing Between List and Set in Java

To decide whether to use List or Set, consider the following guidelines:

1. If you need to maintain the order of elements or allow duplicates, choose List.
2. If you require a collection of unique elements and the order does not matter, choose Set.
3. Consider the operations you need to perform on the collection, such as indexing, adding/removing elements, or checking for duplicates.
4. Evaluate the performance characteristics of List and Set for your specific use case. For example, List may be more efficient for frequent positional access, while Set is more efficient for checking membership or removing duplicates.

Conclusion
List and Set are both powerful Java collection interfaces, each with their own set of characteristics and use cases. A list is an ordered collection with the ability to store duplicate elements, making it appropriate for scenarios requiring positional access and allowing redundancy. Set, on the other hand, provides an unordered collection of distinct elements, making it ideal for tasks such as checking for membership or removing duplicates. Understanding the differences between List and Set will allow you to make informed decisions and choose the best collection type for your Java programs.

Frequently Asked Questions (FAQs)

Here are some of the most frequently asked questions on the difference between List and Set in Java

1. Are duplicate elements allowed in a Set?
No. Sets in Java do not allow duplicate elements. Each element must be unique within the Set.

2. How to maintain the insertion order of elements in a List?
Yes, Lists in Java maintain the order of elements based on their insertion. The elements can be found using their index.

3. Which collection type should be used to retrieve elements by their index?
If you need to retrieve elements by index, you should use a List. Lists provide positional access to elements, allowing you to retrieve or modify them using their index.

4. Does a List contain null elements?
Yes, a List can contain null elements. It is possible to add null values to a List as well as have multiple occurrences of null within the List.