String replaceVowels(String s){
        return s.toLowerCase()   // перевод в нижний регистр по условию задачи
                   .replaceAll("\\.","")  // удаление . во входных данных
                   .replaceAll("[aoyeui]*([^aoyeui])[aoyeui]*", ".$1"); // удаление гласных и замена согласных на значение с точкой
    }

    @Test
    public void testReplaceVowels(){
        assertEquals(".b.b.c.b",replaceVowels("BaBAcAba"));
        assertEquals(".b.c.b",replaceVowels("aBAcAba"));
        assertEquals(".b.b.c.b",replaceVowels("b...aB..AcAba"));
    }

 assertEquals(".b.c.b",replaceVowels("BAcAba"));

.replaceAll("[a|o|e|i|y|u]+",".")  // замена гласной на .
                .replaceAll("(\\.)+",".") // замена повторений . на одиночную .
                .replaceAll("\\.$",""); // удаление последней . в строке

Set<String> toReplace = new HashSet<>(Arrays.asList("a", "o", "e", "i", "y", "u", "."));

String replaceVowels(String text){
        return Pattern.compile("").splitAsStream(text.toLowerCase())
                .filter(s -> !toReplace.contains(s))
                .map(s -> "." + s)
                .collect(Collectors.joining(""));
    }

    @Test
    public void testReplaceVowels(){
        assertEquals(".b.b.b.c.c.c",replaceVowels("aBBBAAACCC"));
        assertEquals(".b.b.c.b",replaceVowels("BaBAcAba"));
        assertEquals(".b.c.b",replaceVowels("aBAcAba"));
        assertEquals(".b.c.b",replaceVowels("BAcAba"));
        assertEquals(".b.b.c.b",replaceVowels("b...aB..AcAba"));
    }

        Set<Character> toReplace = new HashSet<>("aoyeui.".chars().mapToObj(e->(char)e).collect(Collectors.toList()));

        String replaceVowels(String text){
            return text.toLowerCase().chars()
                .mapToObj(i -> (char)i)
                .filter(c -> !toReplace.contains(c))
                .map(s -> "." + s)
                .collect(Collectors.joining(""));
        }

    @Test
    public void testReplaceVowels(){
        assertEquals(".b.b.b.c.c.c",replaceVowels("aBBBAAACCC"));
        assertEquals(".b.b.c.b",replaceVowels("BaBAcAba"));
        assertEquals(".b.c.b",replaceVowels("aBAcAba"));
        assertEquals(".b.c.b",replaceVowels("BAcAba"));
        assertEquals(".b.b.c.b",replaceVowels("b...aB..AcAba"));
    }

    String replaceVowels(String text){
        StringBuilder sb = new StringBuilder(text.length() * 2);
        for(char c : text.toLowerCase().toCharArray()) {
            if("aoyeui.".indexOf(c) < 0) {
                sb.append('.').append(c);
            }
        }
        return sb.toString();
    }

    @Test
    public void testReplaceVowels(){
        assertEquals(".b.b.b.c.c.c",replaceVowels("aBBBAAACCC"));
        assertEquals(".b.b.c.b",replaceVowels("BaBAcAba"));
        assertEquals(".b.c.b",replaceVowels("aBAcAba"));
        assertEquals(".b.c.b",replaceVowels("BAcAba"));
        assertEquals(".b.b.c.b",replaceVowels("b...aB..AcAba"));
    }

    String replaceVowels(String text){
        StringBuilder sb = new StringBuilder(text.length());
        for(char c = text.charAt(0), i =0; i < text.length(); i++, c = i < text.length() ? text.charAt(i) : '.') {
            if('a' != c && 'o' != c && 'y' != c && 'e' != c && 'u' != c && 'i' != c && '.' != c && 'A' != c
                    && 'O' != c && 'Y' != c && 'E' != c && 'U' != c && 'I' != c)
                sb.append('.').append(Character.toLowerCase(c));
        }
        return sb.toString();
    }

    @Test
    public void testReplaceVowels(){
        assertEquals(".b.b.b.c.c.c",replaceVowels("aBBBAAACCC"));
        assertEquals(".b.b.b.c.c.c",replaceVowels("aBBBAAACEiICCyo"));
        assertEquals(".b.b.c.b",replaceVowels("BaBAcAba"));
        assertEquals(".b.c.b",replaceVowels("aBAcAba"));
        assertEquals(".b.c.b",replaceVowels("BAcAba"));
        assertEquals(".b.b.c.b",replaceVowels("b...aB..AcAba"));
    }

    String replaceVowels(String text){
        char[] buffer = new char[text.length() * 2];
        int dataLength = 0;
        for(char c = text.charAt(0), i =0; i < text.length(); i++, c = i < text.length() ? text.charAt(i) : '.') {
            if('a' != c && 'o' != c && 'y' != c && 'e' != c && 'u' != c && 'i' != c && '.' != c && 'A' != c
                    && 'O' != c && 'Y' != c && 'E' != c && 'U' != c && 'I' != c) {
                buffer[dataLength++] = '.';
                buffer[dataLength++] = Character.toLowerCase(c);
            }
        }
        return new String(buffer, 0, dataLength);
    }

    @Test
    public void testReplaceVowels(){
        assertEquals(".b.b.b.c.c.c",replaceVowels("aBBBAAACCC"));
        assertEquals(".b.b.b.c.c.c",replaceVowels("aBBBAAACEiICCyo"));
        assertEquals(".b.b.c.b",replaceVowels("BaBAcAba"));
        assertEquals(".b.c.b",replaceVowels("aBAcAba"));
        assertEquals(".b.c.b",replaceVowels("BAcAba"));
        assertEquals(".b.b.c.b",replaceVowels("b...aB..AcAba"));
    }

    String replaceVowels(String text){
        char[] buffer = new char[text.length() * 2];
        int dataLength = 0;
        for(char c = Character.toLowerCase(text.charAt(0)), i =0; i < text.length(); i++, c = i < text.length() ? Character.toLowerCase(text.charAt(i)) : '.') {
            if('a' != c && 'o' != c && 'y' != c && 'e' != c && 'u' != c && 'i' != c && '.' != c ) {
                buffer[dataLength++] = '.';
                buffer[dataLength++] = c;
            }
        }
        return new String(buffer, 0, dataLength);
    }

    @Test
    public void testReplaceVowels(){
        assertEquals(".b.b.b.c.c.c",replaceVowels("aBBBAAACCC"));
        assertEquals(".b.b.b.c.c.c",replaceVowels("aBBBAAACEiICCyo"));
        assertEquals(".b.b.c.b",replaceVowels("BaBAcAba"));
        assertEquals(".b.c.b",replaceVowels("aBAcAba"));
        assertEquals(".b.c.b",replaceVowels("BAcAba"));
        assertEquals(".b.b.c.b",replaceVowels("b...aB..AcAba"));
    }

Задача:
-удаляет все гласные буквы,
-перед каждой согласной буквой ставит символ ".",
-все прописные согласные буквы заменяет на строчные.

 try {
            for(char c = 0; c >= 0; c = (char) System.in.read()) {
                if (!Character.isISOControl(c) &&
                        c != KeyEvent.CHAR_UNDEFINED && Character.UnicodeBlock.of(c) != null &&
                        Character.UnicodeBlock.of(c) != Character.UnicodeBlock.SPECIALS
                        &&  'a' != c && 'o' != c && 'y' != c && 'e' != c && 'u' != c && 'i' != c && '.' != c
                        && 'A' != c && 'O' != c && 'Y' != c && 'E' != c && 'U' != c && 'I' != c) {
                    System.out.print('.');
                    System.out.print(Character.toLowerCase(c));
                }
            }
        } catch (IOException ignored) {
        }