How to Get ArrayList from Stream in Java 8?

Last Updated : 17 Jul, 2024

Given a Stream, the task is to convert this Stream into ArrayList in Java 8.

Examples:

Input: Stream: [1, 2, 3, 4, 5]
Output: ArrayList: [1, 2, 3, 4, 5]

Input: Stream: ['G', 'e', 'e', 'k', 's']
Output: ArrayList: ['G', 'e', 'e', 'k', 's']

1. Using Collectors.toList() method:

Approach:

Get the Stream to be converted.
Collect the stream as List using collect() and Collectors.toList() methods.
Convert this List into an ArrayList
Return/Print the ArrayList

Below is the implementation of the above approach.

Program: Java

// Java program to convert Stream to ArrayList // using Collectors.toList() method  import java.util.*; import java.util.stream.*;  public class GFG {     // Driver code     public static void main(String args[])     {          Stream<Integer>             stream = Stream.of(1, 2, 3, 4, 5);          // Convert Stream to ArrayList in Java         ArrayList<Integer>             arrayList = new ArrayList<Integer>(stream.collect(Collectors.toList()));          // Print the arraylist         System.out.println("ArrayList: " + arrayList);     } }

Output

ArrayList: [1, 2, 3, 4, 5]

Explanation of the Program:

This Java program demonstrates converting a Stream to an ArrayList using the Collectors.toList method.
In the main method, a Stream of integers is created and then collected into a List, which is used to initialize an ArrayList.
The resulting ArrayList is then printed to the console.

2. Using Collectors.toCollection() method:

Approach:

Get the Stream to be converted.
Collect the stream as ArrayList using collect() and Collectors.toCollection() methods.
Return/Print the ArrayList

Below is the implementation of the above approach.

Program: Java

// Java program to convert Stream to ArrayList // using Collectors.toList() method  import java.util.*; import java.util.stream.*;  public class GFG {      // Function to get ArrayList from Stream     public static <T> ArrayList<T>     getArrayListFromStream(Stream<T> stream)     {          // Convert the Stream to ArrayList         ArrayList<T>             arrayList = stream                             .collect(Collectors                             .toCollection(ArrayList::new));          // Return the ArrayList         return arrayList;     }      // Driver code     public static void main(String args[])     {          Stream<Integer>             stream = Stream.of(1, 2, 3, 4, 5);          // Convert Stream to ArrayList in Java         ArrayList<Integer>             arrayList = getArrayListFromStream(stream);          // Print the arraylist         System.out.println("ArrayList: "                            + arrayList);     } }

Output

ArrayList: [1, 2, 3, 4, 5]

Explanation of the Program:

This Java program converts a Stream to an ArrayList using the Collectors.toCollection method.
The getArrayListFromStream function takes a Stream as input, collects its elements into an ArrayList, and returns it.
In the main method, a Stream of integers is converted into an ArrayList and printed.