String split method returning first element as empty using regex

Question

I'm trying to get the digits from the expression [1..1], using Java's split method. I'm using the regex expression ^\\[|\\.{2}|\\]$ inside split. But the split method returning me String array with first value as empty, and then "1" inside index 1 and 2 respectively. Could anyone please tell me what's wrong I'm doing in this regex expression, so that I only get the digits in the returned String array from split method?

Either update to Java 8 or [do same research](https://www.google.de/search?q=java+split+first+empty). This question is already answered a lot of times. — Tom, Jan 10 '16 at 15:43
Possible duplicate of [Why in Java 8 split sometimes removes empty strings at start of result array?](http://stackoverflow.com/questions/22718744/why-in-java-8-split-sometimes-removes-empty-strings-at-start-of-result-array) — A4L, Jan 10 '16 at 15:43
@cricket_007: I would suggest `\\d+` since the numbers can probably be larger than `9`. — Willem Van Onsem, Jan 10 '16 at 15:44

score 1 · Accepted Answer · answered Jan 10 '16 at 15:42

You should use matching. Change your expression to:

`^\[(.*?)\.\.(.*)\]$`

And get your results from the two captured groups.

As for why split acts this way, it's simple: you asked it to split on the [ character, but there's still an "empty string" between the start of the string and the first [ character.

score 0 · Answer 2 · answered Jan 10 '16 at 15:42

0

Your regex is matching [ and .. and ]. Thus it will split at this occurrences.

You should not use a split but match each number in your string using regex.

answered Jan 10 '16 at 15:42

Marcinek

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score 0 · Answer 3 · edited May 23 '17 at 12:09

You've set it up such that [, ] and .. are delimiters. Split will return an empty first index because the first character in your string [1..1] is a delimiter. I would strip delimiters from the front and end of your string, as suggested here.

So, something like

input.replaceFirst("^[", "").split("^\\[|\\.{2}|\\]$");

Or, use regex and regex groups (such as the other answers in this question) more directly rather than through split.

score 0 · Answer 4 · answered Jan 10 '16 at 15:42

Why not use a regex to capture the numbers? This will be more effective less error prone. In that case the regex looks like:

^\[(\d+)\.{2}(\d+)\]$

And you can capture them with:

Pattern pat = Pattern.compile("^\\[(\\d+)\\.{2}(\\d+)\\]$");
Matcher matcher = pattern.matcher(text);
if(matcher.find()) {  //we've found a match
    int range_from = Integer.parseInt(matcher.group(1));
    int range_to = Integer.parseInt(matcher.group(2));
}

with range_from and range_to the integers you can no work with.

The advantage is that the pattern will fail on strings that make not much sense like ..3[4, etc.

String split method returning first element as empty using regex

4 Answers4