console.log(proporcion(-5, 5, 4, 3, 2, 1, 0, -1));

GREATER_THAN_0 = 0.625
LESS_THAN_0 = 0.25
EQUAL_TO_0 = 0.125

@SuppressWarnings({ "rawtypes", "unchecked" })
    public static Function<Integer, Function<Integer, Function>> myPowerTriFunction = x -> y -> f -> y == 0 ? 1 : x * (Integer) ((Function<Integer, Function<Integer, Function>>) f).apply(x).apply(y - 1).apply(f);
    @SuppressWarnings("unchecked")
    public static BiFunction<Integer, Integer, Integer> myPowerBiFunction = (x, y) -> (Integer) myPowerTriFunction.apply(x).apply(y).apply(myPowerTriFunction);

    public static void main(String[] args) {
        System.out.println(myPowerBiFunction.apply(3, 5)); // prints 243
        System.out.println(myPowerBiFunction.apply(4, 6)); // prints 4096
    }

    public static void printStatistics(int... a) {
        for (NumberValue nv : NumberValue.values()) {
            System.out.println(nv.name() + " = " + sum(nv.getPredicate(), a));
        }
    }

    private static enum NumberValue {
        GREATER_THAN_0, LESS_THAN_0, EQUAL_TO_0;

        private IntPredicate getPredicate() {
            return this == GREATER_THAN_0 ? i -> i > 0 : this == LESS_THAN_0 ? i -> i < 0 : i -> i == 0;
        }
    }

    public static double sum(IntPredicate predicate, int... a) {
        return Arrays.stream(a).filter(predicate).mapToDouble(i -> 1.0 / a.length).sum();
    }

    public static void main(String[] args) {
        printStatistics(-5, 5, 4, 3, 2, 1, 0, -1);
    }

GREATER_THAN_0 = 0.625
LESS_THAN_0 = 0.25
EQUAL_TO_0 = 0.125

public static String toUpperIntV(final String s, final int intervall) {
        final var chars = s.toCharArray();

        for(int i = intervall - 1; i < chars.length; i += intervall) {
            chars[i] = Character.isLowerCase(chars[i]) ? Character.toUpperCase(chars[i]) : Character.toLowerCase(chars[i]);
        }

        return String.valueOf(chars);
    }

System.out.println(toUpperIntV("la casa azul", 1)); // LA CASA AZUL
System.out.println(toUpperIntV("la casa azul", 2)); // lA CaSa aZuL
System.out.println(toUpperIntV("la casa azul", 3)); // la caSa AzuL
System.out.println(toUpperIntV("La Casa Azul", 1)); // lA cASA aZUL
System.out.println(toUpperIntV("La Casa Azul", 2)); // LA caSa AZuL
System.out.println(toUpperIntV("La Casa Azul", 3)); // La CaSa azuL
System.out.println(toUpperIntV("LA CASA AZUL", 1)); // la casa azul
System.out.println(toUpperIntV("LA CASA AZUL", 2)); // La cAsA AzUl
System.out.println(toUpperIntV("LA CASA AZUL", 3)); // LA CAsA aZUl