How do i Convert List to Set

Published May 20, 2022

ArrayLists and HashSets are both supported in Java, and you may choose either based on your specific requirements. The two are quite distinct, and they are used for very different purposes.

The ArrayList is a List interface implementation class used to store data in linear order, while the Set is an interface that contains the HashSet class to store data. The primary distinction between these two is that the HashSet does not permit duplicate entries and only stores unique elements.

This article will go through several methods for converting an ArrayList to a HashSet.

How to convert a List into a Set

There are  three main simple ways you can use to convert a List into a set in Java, they include:

?      Using Naive Approach

?      Using constructors

?      Using Java 8 Stream API

 

Method 1: Using the Naive Approach

This is one of the most common methods for converting a list to a set, and it is preferred by the majority of developers, particularly novices. This method is really straightforward, and it entails the following basic steps:

 

• Step 1: To begin, create an empty set.
• Step 2: Iterate over the list, adding each item to the Set.
• Step 3: Finally, use the HashSet to add the set components.

 

Now, let's use these steps in the example below.

Example

In this example, we'll make a list and save the names of numerous programming IDEs. We also create an empty set called Set.

Then we loop over the list, adding each element to the set one by one. Finally, we print the pieces in the Set

 

import java.util.Arrays; import java.util.HashSet; import java.util.List; import java.util.Set;   public class Convert_Java_to_List_method1 {             public static void main(String[] args) {                                                 List<String> IDElist = Arrays.asList("Android Studio", "Ecclipse", "Netbeans", "Sublime Text");                                                 Set<String> set  = new HashSet<String>();                                                 for(String ele : IDElist){                                                             set.add(ele);                                                 }                                                 for(String ele : set){                                                             System.out.println(ele);                                                 }               }   }

 

Output:

Netbeans Sublime Text Android Studio Ecclipse

 

Method 2: Using constructors

This is another simple method you might do. In this method, you simply need to pass the list that needs to be turned into a HashSet constructor. The constructor then returns a new set containing all of the unique elements. Now consider the following example

 

import java.util.Arrays; import java.util.HashSet; import java.util.List; import java.util.Set;   public class Convert_Java_to_List_method2 {               public static void main(String[] args) {                         List<String> IDElist = Arrays.asList("Android Studio", "Pycham", "Notepad++", "Dreamweaver");                         Set<String> IDEset  = new HashSet<String>(IDElist);                         for(String ele : IDEset){                                     System.out.println(ele);                         }               }   }

 

Output

Pycham Notepad++ Dreamweaver Android Studio

 

In this example, the constructor has removed the necessity for the for loop, which was utilized in the prior approach (method 1).

Method 3: Using Java 8 Stream API

This is the last technique we'll look at in this article. We will employ the Java 8 Stream API to transform the ArrayList into a HashSet. First, we'll transform the list into a stream, and then we'll add a function to the stream.

We will use the Collectors.toSet() method in the collect process to convert it into a set. Take a look at the code below

 

import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; import java.util.Set;   public class Convert_Java_to_List_method3 {               public static void main(String[] args) {         List<String> IDElist = Arrays.asList("Netbeans", "Android studio", "Notepad ++", "Sublime Text");         Set<String> set  = IDElist.stream().collect(Collectors.toSet());         for(String ele : set){             System.out.println(ele);         }                 }   }

 

Output:

Netbeans Android studio Notepad ++ Sublime Text

 

Keywords: How to Convert a List into a Set , Java Collections, Java