How to convert a String to a Java 8 Stream of Char

问题:

I found this question about getting a java.util.streams.IntStream from a java String but I have not found this method now that I'm using Java 8.

Correction: As you guys pointed, I was using Java 7. Now the method chars() is there. But the question still applies:

How can I get a Stream<Character> from a String?

回答1:

I was going to point you to my earlier answer on this topic but it turns out that you've already linked to that question. The other answer also provides useful information.

If you want char values, you can use the IntStream returned by String.chars() and cast the int values to char without loss of information. The other answers explained why there's no CharStream primitive specialization for the Stream class.

If you really want boxed Character objects, then use mapToObj() to convert from IntStream to a stream of reference type. Within mapToObj(), cast the int value to char. Since an object is expected as a return value here, the char will be autoboxed into a Character. This results in Stream<Character>. For example,

Stream<Character> sch = "abc".chars().mapToObj(i -> (char)i);
sch.forEach(ch -> System.out.printf("%c %s%n", ch, ch.getClass().getName()));

a java.lang.Character
b java.lang.Character
c java.lang.Character

回答2:

Please make sure that you are using JDK 8. This method located in CharSequence interface, implemented by String.

This snippet works fine:

import java.util.stream.IntStream;

public class CharsSample {

    public static void main(String[] args) {
        String s =  "123";
        IntStream chars = s.chars();
    }
}