DecimalFormat.java contains following at line 3404
https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/text/DecimalFormat.java#L3404

{code}
} else if (ch == QUOTE) {
    // A quote outside quotes indicates either the
    // opening quote or two quotes, which is a quote
    // literal. That is, we have the first quote in 'do'
    // or o''clock.
    if (ch == QUOTE) {
        if ((pos+1) < pattern.length() &&
            pattern.charAt(pos+1) == QUOTE) {
            ++pos;
            affix.append("''"); // o''clock
        } else {
            inQuote = true; // 'do'
        }
        continue;
    }
{code}

It seems that the second condition is always true.