Лямбда в методе

package oop.third_program;
import static java.lang.System.out;
 
class LowerLetters implements Letters {
 
    public int analyse(String str) {
        int lower = 0;
        for (char c : str.toCharArray())
            if (Character.isLowerCase(c)) lower++;
        return lower;
    }
}
 
class UpperLetters implements Letters {
 
    public int analyse(String str) {
        int upper = 0;
        for (char c : str.toCharArray())
            if (Character.isUpperCase(c)) upper++;
        return upper;
    }
}
 
public class Main {
 
    public static void main(String[] args) {
        Letters test2 = new UpperLetters();
        Letters test3 = new LowerLetters();
 
        out.println(test2.analyse("Test"));
        out.println(test3.analyse("Test"));
 
    }
}
 
 
interface Letters {
    int analyse(String str);
}

interface Counter {
  boolean test(int c);
  default long count(String s) {
    return s.chars().filter(c -> test(c)).count();
  }
}
 
 
final Counter upperCounter = Character::isUpperCase;
final Counter lowerCounter = Character::isLowerCase;
final var s = "AbAbA";
System.out.println(upperCounter.count(s));
System.out.println(lowerCounter.count(s));