Is it possible to replace the following code by lambda:

Question

static TreeMap<Integer, String> parseElementsBeforeOpenBracket(String inValue) {
    StringTokenizer tokenizer = new StringTokenizer(inValue, "[]", true);
    TreeMap<Integer, String> mapElements = new TreeMap<>();
    int i = 0;
    while (tokenizer.hasMoreElements()) {
        String s = (String) tokenizer.nextElement();
        mapElements.put(i, s);
        i += s.length();
    }
    return mapElements;
}

Expecting: something like TreeMap<Integer, String> mapElements = xxx.stream()...Collectors.toMap()

Answer 1

I don't know how to use lambda, but, as the official doc says you can use Mathch and Pattern under java.util.regex package instead of StringTokenizer:

private static final Pattern PATTERN = Pattern.compile("[^\\[\\]]+|\\[|\\]");
    
    public static TreeMap<Integer, String> parseElementsBeforeOpenBracket(String inValue) {
        TreeMap<Integer, String> mapElements = new TreeMap<>();
        Matcher matcher = PATTERN.matcher(inValue);
        int i = 0;
        while (matcher.find()) {
            String s = matcher.group();
            mapElements.put(i, s);
            i += s.length();
        }
        return mapElements;
    }

I tested with ozh22a]xyz4[4b3[3c]]abc5[5]abcde and got the same result as your code {0=ozh22a, 6=], 7=xyz4, 11=[, 12=4b3 , 15=[, 16=3c, 18=], 19=], 20=abc5, 24=[, 25=5, 26=], 27=abcde}

Maybe you can't think of [^\\[\\]]+|\\[|\\] very quickly, but observing your code results can be divided into three parts:

1. Consecutive characters that are not [ or ] -> [^\\[\\]]+
2. [ -> \\[
3. ] -> \\]

\\ is an escape

If you are not familiar with the methods of the Matcher class, please see Module java.base Package java.util.regex Class Matcher.

If you use jdk9 and above, you can use the Matcher.result() method, such as matcher.results().collect(TreeMap::new, (map, matchResult) -> map.put(matchResult.start(), matchResult.group()), TreeMap::putAll);

This can directly get a TreeMap result.

Please see Matcher.results().I didn't test it because I'm using JDK8.

I am not very good at English, I use Google Translate, which may affect reading, please forgive me. Hope to help you.