没有字符的Java字符串（“”）以逗号分隔将返回数组大小1

Question

I have a String with ""(blank data), whenever I try to split the string with comma, I get a list with size 1.

When the String has no object why am I getting list with size 1.

Code :

String abc = "";
String[] t = abc.split(",");
System.out.println(t.length);

Output :

1

Answer 1

Because it needs to have a place to put the "" entry. split is not a lossy operation (other than losing the delimiters).

From the split 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. The substrings in the array are in the order in which they occur in this string. If the expression does not match any part of the input then the resulting array has just one element, namely this string.

When there is a positive-width match at the beginning of this string then an empty leading substring is included at the beginning of the resulting array. A zero-width match at the beginning however never produces such empty leading substring.

(my emphasis)

Answer 2

If you debug inside jdk code of split method, you will find this line from where it returns,

    // If no match was found, return this
    if (off == 0)
        return new String[]{this};

As the comment says it returns an array containing this , in this case this is a blank string and hence you getting an array of size 1, where the first element is blank ie this

In this similar example it returns this which is not blank,

String abc = "abcd";
String[] t = abc.split(",");
System.out.println(t[0]); // prints "abcd" i.e this

Short Answer: // If no match was found, return this

Answer 3

Here is what written in java official docs.

 * 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.  The substrings in
 * the array are in the order in which they occur in this string.  If the
 * expression does not match any part of the input then the resulting array
 * has just one element, namely this string.

So this means that each substring(element that you are placing in the array) is terminated by another substring or end of the string so thatswhy it is giving the size as 1.

Hope this helps to clear your doubt.