static int indexOf(CharSequence cs, int searchChar, int start) {
        if (cs instanceof String) {
            return ((String) cs).indexOf(searchChar, start);
        } else {
            int sz = cs.length();
            if (start < 0) {
                start = 0;
            }
            for (int i = start; i < sz; i++) {
                if (cs.charAt(i) == searchChar) {
                    return i;
                }
            }
            return -1;
        }
    }
<p>Finds the first index in the {@code CharSequence} that matches the
specified character.</p>

@param cs  the {@code CharSequence} to be processed, not null
@param searchChar  the char to be searched for
@param start  the start index, negative starts at the string start
@return the index where the search char was found, -1 if not found
android/android_framework/base/src/main/java/lang3/CharSequenceUtils.java