static functions for filter() and map() in Java 8 - stream

JavaStreamPredicateAndMapper.java

import java.util.function.Function;
import java.util.function.Predicate;
import java.util.regex.Pattern;
import java.util.stream.Stream;
import java.util.Arrays;

/* raw problem and better solution: 
 https://stackoverflow.com/questions/57836937/call-custom-static-functions-from-filter-and-map-in-java-8-stream
*/
class Solution {
    public static void main(String[] args) {
        String[] arr = {"aac", "abc"};
        Stream<String> stream = Arrays.stream(arr);
        stream.filter(DemoFilter.checkPrefixExist("aa")).map(DemoMap.numberOfDistinctCharacters()).forEach(s -> System.out.println(s));
    }
}

class DemoFilter {

    public static Predicate<String> checkPrefixExist(String prefix) {
        Pattern pattern = Pattern.compile(prefix);
        return p -> pattern.matcher(p).find();
    }

}

class DemoMap {
        public static Function<String, Integer> numberOfDistinctCharacters() {
            return s -> (int)s.chars().distinct().count();
    }
}

// better solution: https://stackoverflow.com/questions/57836937/call-custom-static-functions-from-filter-and-map-in-java-8-stream