How To Convert Int[] To Arraylist Inwards Coffee 8? Illustration Tutorial

I in 1 lawsuit asked this interrogation to 1 of the Java developers during Interview too similar many other, he answered that Arrays.asList() tin convert an array of primitive integer values to ArrayList<Integer> inwards Java, which was genuinely wrong. Even though, Arrays.asList() is the go-to method to convert an array to ArrayList inwards Java when it comes to converting a primitive array to ArrayList, this method is non useful. The Arrays.asList() method does non bargain amongst boxing too it volition only exercise a List<int[]> which is non what y'all want. In fact, at that topographic point was no shortcut to convert an int[] to ArrayList<Integer> or long[] to ArrayList<Long> till Java 8.

From JDK 8 onwards, y'all either hade to brand a utility method or demand to job full general purpose Java libraries similar Google Guava or Apache Commons to convert an array of primitive values like. byte, short, char, int, long, float, too double to ArrayList of Byte, Character, Short, Integer, Long, Float, too Double wrapper classes.

Though from Java 8 onwards, y'all tin job the java.util.Stream to convert an int[] to ArrayList<Integer>. There are specialized current implementations for primitive information types similar IntStream for primitive int, LongStream for primitive long too DoubleStream for primitive double, which tin convert an array of primitive values to a current of primitive values.

Once y'all acquire the Stream of int values, y'all tin job boxed() method to convert it to Stream of Integer wrapper objects. After that y'all tin only convert Stream to List every bit shown inwards that article i.e. y'all tin job collect() method of the current amongst Collectors.toList() to acquire a List.

int[] to List

If y'all desire ArrayList instead of List hence y'all tin top a Supplier to Collectors, which volition accumulate elements into an ArrayList every bit shown below:

int[] primes = novel int[]{2, 3, 5, 7, 11, 13, 17};
ArrayList<Integer> listing = IntStream.of(primes)
              .boxed().collect(Collectors.toCollection(ArrayList::new));


Alternatively, y'all tin too job the re-create constructor of Collection interface to exercise an ArrayList past times copying all elements from the List event every bit shown inwards next example:

List<Integer> listing = IntStream.of(primes).boxed().collect(Collectors.toList());
ArrayList<Integer> arraylist = novel ArrayList<>(list);


What is this code doing? Well, if y'all are non real familiar amongst Java 8, Stream too method reference hence hither is a measuring past times measuring explanation of to a higher house one-liner of converting a primitive array to ArrayList inwards JDK 8:

1) The IntStream.of(primes) is converting an int array to IntStream object.

2) The boxed() method of IntStream convert applies boxing on each chemical constituent of IntStream too furnish a Stream of Integer i.e it converts IntStream to Stream<Integer> object.

3) The collect() method collects all elements of Stream into whatsoever Collection class past times using Collectors of Java 8. H5N1 Collector encapsulates the functions used every bit arguments to collect(Supplier, BiConsumer, BiConsumer), allowing for reuse of collection strategies too composition of collect operations such every bit multiple-level grouping or partitioning.

4) The Collectors.toCollection() method collects elements of Stream into a Collection which is specified past times the showtime parameter. Here nosotros are passing ArrayList::new which is a constructor reference, which way all elements of Stream volition hold upward collected into an ArrayList. See The Complete Java MasterClass to larn more.

How to convert int[] to ArrayList of Integer inwards Java 8

By far, That was the simplest way to convert an array of primitive information types to List of wrapper objects similar an array of ints to ArrayList of Integers.

Btw, at that topographic point is some other way to convert a primitive array to ArrayList inwards Java 8 past times using Arrays.stream() method, which converts an array to Stream inwards Java 8. This method is equivalent to IntStream.of(int[]) and furnish an IntStream. The residuum of the code volition rest same i.e. y'all tin job the next one-liner to convert an int[] to ArrayList inwards JDK 8:


ArrayList<Integer> listing = Arrays.stream(ints).boxed().collect(Collectors.toCollection(ArrayList::new));

Here is the total Java computer program to convert an int[] to ArrayList<Integer> inwards Java 8:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

/*
* Java Program to convert a long[] to ArrayList<Long> inwards JDK 8
*/

public class Main {

public static void main(String[] args) throws Exception {

// converting an array of Integer to arrayList of Integer
int[] primes = novel int[]{2, 3, 5, 7, 11, 13, 17};
System.out.println("primitive int array: " + Arrays.toString(primes));

ArrayList<Integer> listOfInts = IntStream.of(primes).boxed().collect(Collectors.toCollection(ArrayList::new));
System.out.println("ArrayList<Integer> : " + listOfInts);

long[] numbers = novel long[]{202, 3003, 2002, 3003, 222};
ArrayList<Long> listOfLong = Arrays.stream(numbers).boxed().collect(Collectors.toCollection(ArrayList::new));
System.out.println("primitive long array: " + Arrays.toString(numbers));
System.out.println("ArrayList<Long> : " + listOfLong);
}

}

Output:
primitive int array: [2, 3, 5, 7, 11, 13, 17]
ArrayList<Integer> : [2, 3, 5, 7, 11, 13, 17]
primitive long array: [202, 3003, 2002, 3003, 222]
ArrayList<Long> : [202, 3003, 2002, 3003, 222]

From the output, it's clear that both ways of converting an array of primitive values to ArrayList of objects piece of work fine. You tin job whatever y'all want.  See example)

How to job forEach() method inwards Java 8 (example)

How to job filter() method inwards Java 8 (tutorial)

5 Books to Learn Java 8 from Scratch (books)

Java 8 - Stream.collect() Example (example)

How to job Stream class inwards Java 8 (tutorial)

What is double colon operator of Java 8? (tutorial)

How to bring together String inwards Java 8 (example)

20 Examples of Date too Time inwards Java 8 (tutorial)

10 Free Courses for Experienced Java Programmers (courses)

How to job peek() method inwards Java 8 (example)

Java 8 Stream.findFirst() + filter() representative (see)

How to form the may past times values inwards Java 8? (example)

How to convert List to Map inwards Java 8 (solution)

Difference betwixt abstract class too interface inwards Java 8? (answer)

How to job peek() method inwards Java 8 (example)

How to format/parse the appointment amongst LocalDateTime inwards Java 8? (tutorial)

5 Free Courses to larn Java 8 too nine (courses)

In general, y'all should job Stream if y'all are using Java 8, it's cleaner than the Java half-dozen approach too too takes only 1 describe of piece of work to convert a primitive array to ArrayList. If y'all don't know much virtually Stream too Java 8, I propose y'all read a expert mass on Java 8 to larn to a greater extent than about IntStream and other Stream features like Java 8 inwards Action.

Thanks a lot for reading this article hence far. If y'all similar this article hence delight portion amongst your friends too colleagues. If y'all cause got whatsoever interrogation or feedback hence delight driblet a comment.