Java Stream API filter

harp1814 :

I have code:

static void doSmth() {
    ArrayList<String> list = new ArrayList<>();
    for (int i = 0; i < 30; i++) {
        list.add(String.valueOf(i));
    }
    list.stream().filter("1329"::contains).map(s -> s + "a").forEach(System.out::println);
}

Why i got:

 1a
 2a
 3a
 9a
 13a
 29a

I expected a empty output, because list doesn't contains "1329".

YCF_L :

because

.filter("1329"::contains)

mean

.filter(s -> "1329".contains(s))

not

.filter(s -> s.contains("1329"))

As I guess you think it means.

So your list hold :

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, ... 25, 26, 27, 28, 29]
    ^  ^  ^                 ^               ^                           ^

Which "1329" contains 1,2, 3, 9, 13 and 29