EPI: Extended Simple Regular Expression

ESRE - Extended Simple Regular Expression
static boolean isMatchHere(String r, String s) {
// Case (1.)
if (r.isEmpty()) {
return true;
}

// Case (2) : ends with '$'.
if ("$".equals(r)) {
return s.isEmpty();
}

// Case (4.)
if (r.length() >= 2 && r.charAt(1) == '*') {
for (int i = 0; i < s.length()
&& (r.charAt(0) == '.' || r.charAt(0) == s.charAt(i)); ++i) {
if (isMatchHere(r.substring(2), s.substring(i + 1))) {
return true;
}
}
return isMatchHere(r.substring(2), s);
}

// Case (3.)
return !s.isEmpty()
&& (r.charAt(0) == '.' || r.charAt(0) == s.charAt(0))
&& isMatchHere(r.substring(1), s.substring(1));
}

static boolean isMatch(String r, String s) {
// Case (2.) : starts with '^'.
if (r.charAt(0) == '^') {
return isMatchHere(r.substring(1), s);
}

for (int i = 0; i <= s.length(); ++i) {
if (isMatchHere(r, s.substring(i))) {
return true;
}
}
return false;
}