FRQ-style string methods

FRQ Question 1 Part B says: "the method requires calling String methods." The recurring shapes:

Count characters matching a rule:

public static int countChar(String s, char target) {
    int count = 0;
    for (int i = 0; i < s.length(); i++) {
        if (s.charAt(i) == target) {
            count++;
        }
    }
    return count;
}

Extract or transform pieces:

public static String firstHalf(String s) {
    return s.substring(0, s.length() / 2);
}

Reverse by building backwards:

public static String reverse(String s) {
    String out = "";
    for (int i = s.length() - 1; i >= 0; i--) {
        out += s.charAt(i);
    }
    return out;
}

Check a property of every character (all digits? any uppercase?) — the early-exit pattern:

public static boolean allDigits(String s) {
    for (int i = 0; i < s.length(); i++) {
        if (!Character.isDigit(s.charAt(i))) {
            return false;
        }
    }
    return true;    // only reached when nothing failed
}

Notice return true lives after the loop: it is the "survived every test" case, not a special input.