Want to create a stream of characters from char array in java

Question

From a char array, I want to construct a stream to use java 8 features such as filters and maps.

char[] list = {'a','c','e'};
Stream<Character> cStream = Stream.of(list);
// Stream<Character> cStream = Arrays.stream(list);

The first method does not work (Reason: change cStream to Stream<char[]>). The commented line does not also work (Reason: The method stream(T[]) in the type Arrays is not applicable for the arguments (char[])).

I know that if char[] list is changed to int[], everything works fine using IntStream. But I do not want to convert every char[] to int[] each time or change into a list when I need to use stream library on char array.

possible duplicate of Why is String.chars() a stream of ints in Java 8? — heenenee
– heenenee, Commented Jul 22, 2015 at 4:58
@heenenee That's certainly related, but I wouldn't call it a duplicate. — Jeffrey
– Jeffrey, Commented Jul 22, 2015 at 5:10
Although the other question is focused on why, the how is explained in its accepted answer. A single google search would've turned this up, and I guess I'm going by meta.stackoverflow.com/a/261593/2646526 — heenenee
– heenenee, Commented Jul 22, 2015 at 5:23

Alexis C. · Accepted Answer · 2015-07-22 08:03:17Z

58

You can use an IntStream to generate the indices followed by mapToObj:

char[] arr = {'a','c','e'};
Stream<Character> cStream = IntStream.range(0, arr.length).mapToObj(i -> arr[i]);

answered Jul 22, 2015 at 8:03

Alexis C.

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Comments

Lars Hartviksen · Accepted Answer · 2016-07-20 11:03:55Z

55

A way to do this is via a String object:

char[] list = {'a','c','e'};
Stream<Character> charStream = new String(list).chars().mapToObj(i->(char)i);

I like to do it this way because all the complexity of transforming the array is wrapped into the String creation, and the wrapping of char is also performed behind the scene for me so I can focus on the business logic.

answered Jul 20, 2016 at 11:03

Lars Hartviksen

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2 Comments

Holger Over a year ago

Semantically not different to this answer, except that using CharBuffer.wrap(list) is more efficient than new String(list) as it does not involve copying the array resp., starting with Java 9, converting the char array to a byte array and converting it back while streaming. Under Java 8, the difference is even bigger as String.chars() has been poorly implemented whereas CharBuffer.chars() has an efficient implementation. That has been solved with Java 9, but the copying/conversion overhead of new String(char[]) remains.

JakeRobb Over a year ago

Note that sometimes, when you have an array of characters, it's because it's a sensitive value (like a password), and you're explicitly avoiding instantiating a String. stackoverflow.com/questions/8881291/…

Tagir Valeev · Accepted Answer · 2015-07-27 09:17:04Z

39

A short and efficient way to create an IntStream from char[] array is to use java.nio.CharBuffer:

char[] list = {'a','c','e'};
IntStream stream = CharBuffer.wrap(list).chars();

This way you can use an IntStream interpreting the int values as characters. If you want a boxed Stream<Character> (which may be less efficient), use

Stream<Character> stream = CharBuffer.wrap(list).chars().mapToObj(ch -> (char)ch);

Using CharBuffer can be a little bit faster than IntStream.range as it has custom spliterator inside, so it does not have to execute an additional lambda (possibly as slow polymorphic call). Also it refers to the char[] array only once and not inside the lambda, so it can be used with non-final array variable or function return value (like CharBuffer.wrap(getCharArrayFromSomewhere()).chars()).

answered Jul 27, 2015 at 9:17

Tagir Valeev

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1 Comment

RedCrafter LP Over a year ago

I really like that solution since it doesn't copy the elements of array while still avoiding autoboxing.

TJ Mazeika · Accepted Answer · 2015-07-22 05:34:32Z

3

The simplest change you can make to the code is change char[] to Character[].

Another way is to create a new ArrayList of the boxed chars:

char[] list = {'a','c','e'};
List<Character> listArray = new ArrayList<>();
for (char c : list)
    listArray.add(c);
Stream<Character> cStream = listArray.stream();

In addition, you can use Google Guava's Chars class, to replace the for loop with:

List<Character> listArray = Chars.asList(list);

edited Jul 22, 2015 at 5:34

answered Jul 22, 2015 at 5:29

TJ Mazeika

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Comments

Fzum · Accepted Answer · 2021-10-21 14:16:49Z

2

"ABCDEFGHIJKLMNOPQRSTUVWXYZ".chars().mapToObj(i -> (char) i);

answered Oct 21, 2021 at 14:16

Fzum

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Asif Malek · Accepted Answer · 2022-01-25 20:48:34Z

2

How about a workaround: char[] list = {'a','c','e'};

Arrays.asList(list).stream();

answered Jan 25, 2022 at 20:48

Asif Malek

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1 Comment

jcsahnwaldt Reinstate Monica Over a year ago

Downvote. You didn't even try this. It doesn't do what you think it does.

branboyer · Accepted Answer · 2022-10-02 13:21:29Z

2

Another way not mentioned: make a new String

char[] arr = {'a','c','e'};
new String(arr).chars().mapToObj(i -> (Character) (char) i);

answered Oct 2, 2022 at 13:21

branboyer

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Arpan Saini · Accepted Answer · 2019-10-23 20:19:03Z

1

Getting substream of Characters

 String givenString = "MyNameIsArpan";

       Object[] ints = givenString.chars().mapToObj(i -> (char)i).toArray();

       String subString = Arrays.stream(ints,2,6).
                             map(i -> (char)i).
                             map(String::valueOf).
                             collect(Collectors.joining());

      System.out.println(subString);

OUTPUT : Name

answered Oct 23, 2019 at 20:19

Arpan Saini

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navnath · Accepted Answer · 2021-08-03 12:03:22Z

0

Using Stream Builder:

String inputString = "This is string";
Stream.Builder<Character> charStreamBuilder = Stream.builder();
for (char i :inputString.toCharArray()) {
   charStreamBuilder.accept(i);
 }
 Stream<Character> characterStream = charStreamBuilder.build();

answered Aug 3, 2021 at 12:03

navnath

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Comments

Rakesh Chauhan · Accepted Answer · 2018-09-13 20:37:27Z

-6

I believe the simplest way to convert to Character stream is

    char[] list = {'a','c','e'};

    Stream<Character> characters = Stream.ofAll(list);

answered Sep 13, 2018 at 20:37

Rakesh Chauhan

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2 Comments

Didier L Over a year ago

Although interesting, this answer is not valid because the question is about JDK Steams, and it seems you are referring to javaslang streams.

Arefe Over a year ago

If someone needs to know, he is referring to the www.vavr.io

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