Java Streams，仅过滤前“ N”个匹配项

Question

is there any way to filter only the first 'n' matches using java streams?

for example, if we have this code:

List<String> words = Arrays.asList("zero","one","two","three","four","five","one","one");

List<String> filteredWords = words.stream()
                .filter(word->!word.equals("one"))//filter all "one" strings..
                .collect(Collectors.toList());

System.out.println(filteredWords);

this will filter all "one" strings from the word stream.

So, how to filter only the first 'n' matches and keep the rest of the stream intact?

in other words, if n=1 then, the program should output

"zero","two","three","four","five","one","one"

if n=2 then

"zero","two","three","four","five","one"

Answer 1

You can create a class doing the filtering for you

class LimitedFilter<T> implements Predicate<T> {
    int matches = 0;
    final int limit;
    private Predicate<T> delegate;
    public LimitedFilter<T>(Predicate<T> p, int limit) { 
        delegate = p; this.limit = limit;
    }
    public boolean test(T toTest) {
        if (matches > limit) return true;
        boolean result = delegate.test(toTest);
        if (result) matches++;
        return result;
    }
}

and then use it to filter

Predicate<String> limited = new LimitedFilter<>(w -> !"one".equals(w), 5);
List<String> filteredWords = words.stream()
            .filter(limited) //filter first five "one" strings..
            .collect(Collectors.toList());

Answer 2

This may Help full for you check it out

 List<String> 
words = Arrays.asList("zero","one","two","three","four","five","one","one");

    Stream<String> sortedList =  words.stream().filter(word -> 
     word.contains("n"));

    sortedList.forEach(str->System.out.println(str));