How to Convert Stream to List in Java

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Mohammad Irfan Feb 02, 2024
Java Java Stream Java List
  1. Convert Stream to List Using the collect() Method in Java
  2. Convert Stream to List Using toCollection() Method in Java
  3. Convert Stream to List Using forEach() Method in Java
  4. Convert Stream to List Using toArray() Method in Java
How to Convert Stream to List in Java

This tutorial introduces the conversion of the Stream to a List in Java.

A Stream is a collection of objects. A Stream doesn’t store any data, and therefore it is not a data structure.

The Stream was added to the Java 8 version, whereas a List is an interface that stores ordered collections. In this tutorial, we will look into converting a Stream to a List.

Java has the following ways using which we can achieve our task:

  • Convert using collect() method
  • Convert using toCollection() method
  • Convert using forEach() method
  • Convert using toArray() method

Convert Stream to List Using the collect() Method in Java

The Stream collect() operation is a terminal operation. A terminal operation means that the Stream is consumed and cannot be used further after this operation.

The syntax of this method is:

collect(Collector<? super T, A, R> collector)

This method takes a Collector object as an argument.

The Collector class is used to collect the elements of the Stream into a collection. This class has the toList() method, which converts the Stream to a List.

Let’s now look at a code example:

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class SimpleTesting {
  public static void main(String args[]) {
    // declaring a stream
    Stream<String> furnitures =
        Stream.of("chair", "dinning table", "study table", "coffee table", "sofa");

    // changing stream to list
    List<String> furniture_list = furnitures.collect(Collectors.toList());

    // printing the list
    for (String furniture : furniture_list) {
      System.out.println(furniture);
    }
  }
}

Output:

chair
dinning table
study table
coffee table
sofa

Convert Stream to List Using toCollection() Method in Java

This example is similar to the previous one except that we used the Collector.toList() method instead of the Collectors.toCollection() method.

The Collector class has a method called toCollection() which returns a Collector that gathers the input items into a new Collection in the order they were encountered. Look at the example code below:

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class SimpleTesting {
  public static void main(String args[]) {
    // declaring a stream
    Stream<String> furnitures =
        Stream.of("chair", "dinning table", "study table", "coffee table", "sofa");

    // changing stream to list
    List<String> furniture_list = furnitures.collect(Collectors.toCollection(ArrayList::new));

    // printing the list
    for (String furniture : furniture_list) {
      System.out.println(furniture);
    }
  }
}

Output:

chair
dinning table
study table
coffee table
sofa

Convert Stream to List Using forEach() Method in Java

In this example, we first created an empty ArrayList then used the forEach() method to add each Stream element to the List one by one. The Stream has a method called forEach() that performs on all the elements of the input Stream.

Look at the example code below:

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class SimpleTesting {
  public static void main(String args[]) {
    // declaring a stream
    Stream<String> furnitures =
        Stream.of("chair", "dinning table", "study table", "coffee table", "sofa");

    // declaring an empty arraylist
    ArrayList<String> furniture_list = new ArrayList<>();

    // adding elements one by one
    furnitures.forEach(furniture_list::add);

    // printing the list
    for (String furniture : furniture_list) {
      System.out.println(furniture);
    }
  }
}

Output:

chair
dinning table
study table
coffee table
sofa

Convert Stream to List Using toArray() Method in Java

In this example, we first converted the Stream into an array using the toArray() method. After this, we converted the newly created array to a List using the asList() method to get a list.

Look at the code below:

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class SimpleTesting {
  public static void main(String args[]) {
    // declaring a stream
    Stream<String> furnitures =
        Stream.of("chair", "dinning table", "study table", "coffee table", "sofa");

    // converting stream to array
    String[] furniture_array = furnitures.toArray(String[] ::new);

    // converting array to list
    List<String> furniture_list = Arrays.asList(furniture_array);

    // printing the list
    for (String furniture : furniture_list) {
      System.out.println(furniture);
    }
  }
}

Output:

chair
dinning table
study table
coffee table
sofa

Related Article - Java Stream

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