A minimal example of modern Java: type inference, streams, static methods as arguments etc.

LetterIntersperser.java

package org.example;

import java.util.Arrays;
import java.util.Random;
import java.util.function.Function;
import java.util.stream.Collectors;


public class LetterIntersperser {
    private boolean def;
    private boolean current;

    private LetterIntersperser() {
        this.def = (new Random().nextInt(1)) == 1;
        this.current = this.def;
    }

    private Function<String, String> next() {
        this.current = !this.current;
        return this.current ? String::toLowerCase : String::toUpperCase ;
    }

    public static String call(String str) {
       var intersperser = new LetterIntersperser();
       return Arrays.stream(str.split(""))
               .map(i -> intersperser.next().apply(i) )
               .collect(Collectors.joining(""));
    }
}

Main.java

package org.example;

import java.util.Arrays;

public class Main {

    public static void main(String[] args) {
        var myList = "foo bar baz flannel";
        Arrays.stream(myList.split(" "))
                .sorted()
                .map(LetterIntersperser::call)
                .forEach(str -> System.out.println(str));
    }
}