Difference between List and Set interface in Java

This post will discuss the difference between the List and Set interface in Java.

Two of the most widely used types of collections in Java are List and Set, which both extend the Collection interface. However, List and Set also have some significant differences and trade-offs that make them suitable for different scenarios and use cases.

1. Overview of `List` interface in Java

The List interface is one of the most commonly used interfaces in Java and belongs to the java.util package that extends the Collection interface. It is an ordered collection of elements that allows duplicates. It offers many benefits:

The List interface allows fast access to elements by using the index of the elements. It uses an array to store the elements. When we insert or retrieve an element from the List, we use the index to find the position of the element in the array.
The List interface maintains the order of the elements in the collection. This means that the elements in a List are stored in a sequential order according to their insertion order.
The List interface allows null and duplicate elements in the collection. This means that we can insert, retrieve, or remove null or duplicate values from a List without any problem.
The List interface provides additional methods to manipulate the collection, such as add(), remove(), get(), set(), indexOf(), lastIndexOf(), subList(), sort(), etc. These methods allow us to add, update, delete, or check elements in the collection.

Let’s see an example of how to create and use a List in Java:

import java.util.ArrayList;

import java.util.List;

class Main

{

public static void main(String[] args)

{

// Create a List object

List<String> list = new ArrayList<>();

// Add some elements to the list

list.add("Aaron");

list.add("Bella");

list.add("Casey");

list.add("Aaron");

// Print the list

System.out.println("List: " + list); // [Aaron, Bella, Casey, Aaron]

// Get the element at index 1

System.out.println("Element at index 1: " + list.get(1)); // Bella

// Set the element at index 2

list.set(2, "David");

// Print the updated list

System.out.println("List: " + list); // [Aaron, Bella, David, Aaron]

// Remove the element at index 3

list.remove(3);

// Print the updated list

System.out.println("List: " + list); // [Aaron, Bella, David]

// Check if an element exists in the list

System.out.println("Contains Aaron: " + list.contains("Aaron")); // true

// Add a null element to the list

list.add(null);

// Print the updated list

System.out.println("List: " + list); // [Aaron, Bella, David, null]

}

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2. Overview of `Set` interface in Java

The Set interface is another commonly used interface in Java that belongs to the java.util package and extends the Collection interface. It can be either ordered or unordered, depending on the implementation. For example, HashSet implementation is unordered, LinkedHashSet implementation is ordered, and TreeSet implementation is ordered by natural order or by provided comparator. The elements in a Set can be of any type, and it offers some benefits:

The Set interface allows fast access to elements. Depending upon the implementation, a Set uses an array or a tree structure to store the elements, where each element is stored as a node in the array or tree. When we insert or retrieve an element from the Set, we use the element to calculate its hash code or compare with other nodes and find its position in the array or tree.
The Set interface does not maintain any order of the elements in the collection. This means that the elements in a Set are stored based on their hash code or natural ordering or by a provided Comparator, depending upon the implementation.
The Set interface does not allow duplicate elements in the collection. However, it allows a single null element in the collection.
The Set interface provides additional methods to manipulate the collection, such as add(), remove(), contains(), size(), clear(), etc. These methods allow us to add, delete, or check elements in the collection.

Let’s see an example of how to create and use a Set in Java:

import java.util.HashSet;

import java.util.Set;

class Main

{

public static void main(String[] args)

{

// Create a Set object

Set<String> set = new HashSet<String>();

// Add some elements to the set

set.add("Aaron");

set.add("Bella");

set.add("Casey");

// Print the set

System.out.println("Set: " + set); // [Bella, Aaron, Casey]

// Try to add a duplicate element to the set

set.add("Aaron");

// Print the set

System.out.println("Set: " + set); // [Bella, Aaron, Casey]

// Remove an element from the set

set.remove("Bella");

// Print the updated set

System.out.println("Set: " + set); // [Aaron, Casey]

// Check if an element exists in the set

System.out.println("Contains Aaron: " + set.contains("Aaron")); // true

// Add a null element to the set

set.add(null);

// Print the updated set

System.out.println("Set: " + set); // [null, Aaron, Casey]

}

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3. Difference between `List` and `Set` interface in Java

Here are some of the main differences between List and Set interface in Java:

The List interface is an ordered sequence of elements, whereas the Set represents a distinct collection of elements that can be either ordered or unordered, depending on the implementation.
The List interface maintains the order of the elements in the collection according to their insertion order, whereas the Set interface does not maintain any order of the elements in the collection according to their hash code or natural ordering or by a provided Comparator.
The List interface allows duplicate elements, whereas the Set can contains only distinct elements.
The List interface allows null elements in the collection, whereas the Set interface allows at most one null elements in the collection.
Several List implementations implement the RandomAccess interface, a marker interface to support constant-time random access. Whereas, none of the Set implementations can implement the RandomAccess interface.
The List interface provides a special iterator ListIterator to facilitate bidirectional access which is not available for Set interface.
Popular implementation of List interface includes ArrayList and LinkedList, while that of Set interface includes HashSet, TreeSet, and LinkedHashSet.

4. What to use and when?

As we have seen, List and Set interface are both useful interfaces in Java. Here are some general recommendations on how to choose between them:

If you need to store a collection of elements where duplicates are allowed and order is maintained, we can use List interface.
If you need to store a collection of elements where duplicates are not allowed and order is also not important, we should use Set interface.
If you need to store a collection of elements where duplicates are not allowed and order is important, we should use SortedSet instead. This interface will ensure that the collection is sorted and unique and prevent any data inconsistency or concurrency issues.

In general, a List should be used when the insertion order of elements needs to be maintained. Use a set if we need to maintain a collection that contains no duplicate elements.

That’s all about the differences between the List and Set interface in Java.

Difference between List and Set interface in Java

1. Overview of List interface in Java

2. Overview of Set interface in Java

3. Difference between List and Set interface in Java

4. What to use and when?

1. Overview of `List` interface in Java

2. Overview of `Set` interface in Java

3. Difference between `List` and `Set` interface in Java