Why is String.chars() a stream of ints in Java 8?

java string java-8
Adam Dyga picture Adam Dyga · Mar 16, 2014 · Viewed 89.7k times · Source

In Java 8, there is a new method String.chars() which returns a stream of ints (IntStream) that represent the character codes. I guess many people would expect a stream of chars here instead. What was the motivation to design the API this way?

Answer

skiwi picture skiwi · Mar 16, 2014

As others have already mentioned, the design decision behind this was to prevent the explosion of methods and classes.

Still, personally I think this was a very bad decision, and there should, given they do not want to make CharStream, which is reasonable, different methods instead of chars(), I would think of:

  • Stream<Character> chars(), that gives a stream of boxes characters, which will have some light performance penalty.
  • IntStream unboxedChars(), which would to be used for performance code.

However, instead of focusing on why it is done this way currently, I think this answer should focus on showing a way to do it with the API that we have gotten with Java 8.

In Java 7 I would have done it like this:

for (int i = 0; i < hello.length(); i++) {
    System.out.println(hello.charAt(i));
}

And I think a reasonable method to do it in Java 8 is the following:

hello.chars()
        .mapToObj(i -> (char)i)
        .forEach(System.out::println);

Here I obtain an IntStream and map it to an object via the lambda i -> (char)i, this will automatically box it into a Stream<Character>, and then we can do what we want, and still use method references as a plus.

Be aware though that you must do mapToObj, if you forget and use map, then nothing will complain, but you will still end up with an IntStream, and you might be left off wondering why it prints the integer values instead of the strings representing the characters.

Other ugly alternatives for Java 8:

By remaining in an IntStream and wanting to print them ultimately, you cannot use method references anymore for printing:

hello.chars()
        .forEach(i -> System.out.println((char)i));

Moreover, using method references to your own method do not work anymore! Consider the following:

private void print(char c) {
    System.out.println(c);
}

and then

hello.chars()
        .forEach(this::print);

This will give a compile error, as there possibly is a lossy conversion.

Conclusion:

The API was designed this way because of not wanting to add CharStream, I personally think that the method should return a Stream<Character>, and the workaround currently is to use mapToObj(i -> (char)i) on an IntStream to be able to work properly with them.

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