return A.length == 0 ? [] : A.split(",");

 public String[] split(CharSequence input, int limit) {
        int index = 0;
        boolean matchLimited = limit > 0;
        ArrayList<String> matchList = new ArrayList<String>();
        Matcher m = matcher(input);
 
        // Add segments before each match found
        while(m.find()) {
            if (!matchLimited || matchList.size() < limit - 1) {
                String match = input.subSequence(index, m.start()).toString();
                matchList.add(match);
                index = m.end();
            } else if (matchList.size() == limit - 1) { // last one
                String match = input.subSequence(index,
                                                 input.length()).toString();
                matchList.add(match);
                index = m.end();
            }
        }
 
        // If no match was found, return this
        if (index == 0)
            return new String[] {input.toString()};

split方法的源码。因为正则匹配不到字符。。。就直接返回一个数组 ，数组中包着 空字符串 所以他的长度是1
其实你可以对A进行判断是否是空字符串，空字符串就直接赋值空数组

判断字符串是否为空，为空则返回空数组，如果不为空则返回数组