String split method behavior

Question

I don't see why does the following output makes sense.

String split method on an empty String returning an array of String with length 1

String[] split = "".split(",");
System.out.println(split.length);
Returns array of String with length 1

String[] split = "Java".split(",");
System.out.println(split.length);
Returns array of String with length 1

How to differentiate??

Answer 1

From the documentation:

The array returned by this method contains each substring of this string that is terminated by another substring that matches the given expression or is terminated by the end of the string.

To answer your question, it does what it is expected to do: the returned substring is terminated by the end of the input string (as there was no , to be found). The documentation also states:

If the expression does not match any part of the input then the resulting array has just one element, namely this string.

Note that this is a consequence of the first statement. It is not an additional circumstance that the Java developers added in case the search string could not be found.

Answer 2

I hit this, too. What it's returning is the string up to but not including the split character. If you want to get no strings, use StringTokenizer:

StringTokenizer st = new StringTokenizer(someString,',');
int numberOfSubstrings = st.countTokens();

Answer 3

It's returning the original string (which in this case is the empty string) since there was no , to split on.