gistfile1.txt

public class StringModifierDemo {
    public static void main(String[] args) {
        StringModifier stringModifier = s -> s.toUpperCase() + "!";

        String stringFirst = "aaaaa";
        String stringLast = stringModifier.modify(stringFirst);
        System.out.println(stringLast);

    }
}

@FunctionalInterface
  interface StringModifier {
    String modify(String s);
}