How to split a comma-delimited string into an array of empty strings

Question

I want to split ",,," to a array of 4 "" using the String.split()

Here is my code:

String str = ",,,";     
String[] tokens = str.split(",");

However, the result tokens were an an empty array: [], rather than an array of 4 "" (["","","",""]) as I wanted.

I have tested to change the str a little bit:

String str = ",,,1";        
String[] tokens = str.split(",");

This time the result tokens were ["","","","1"] . This is close to what I want, but I really do not want to add this "1" before doing the split.

The problem is basically, the String.split() will return an empty array if it contains only empty elements "" .

Can you help solve the problem?

Answer 1

You need to use the overloaded String#split(regex, limit) method which takes in the limit parameter.

String[] tokens = str.split(",", -1);

From the docs (emphasis mine):

The limit parameter controls the number of times the pattern is applied and therefore affects the length of the resulting array. If the limit n is greater than zero then the pattern will be applied at most n - 1 times, the array's length will be no greater than n, and the array's last entry will contain all input beyond the last matched delimiter. If n is non-positive then the pattern will be applied as many times as possible and the array can have any length. If n is zero then the pattern will be applied as many times as possible, the array can have any length, and trailing empty strings will be discarded.

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Explanation: When you do not provide the limit argument or provide "zero" as the limit, the split() discards trailing empty fields. When you provide a positive limit argument, it limits the number of fields to that particular limit. But when you provide a negative limit, the split() method allows any number of fields and also not discarding the trailing empty fields. To be more clear, have a look at the source code of the Pattern#split(regex, limit) which has this snippet at the end(comments have been added by me and were not present in the actual source code).

if (limit == 0) // When zero or no arg is given
    while (resultSize > 0 && matchList.get(resultSize-1).equals("")) // if trailing entries are blank
        resultSize--; // remove them out

Note: If you do not provide any limit argument, the split() method without limit argument calls the overloaded split() method like this .

public String[] split(String regex) {
    return split(regex, 0);
}

And also note that, String#split(regex, limit) internally calls the Pattern#split(regex, limit) .