Java列表 <String> 空时返回1

Question

Why does the following code return 1 when I pass in an empty String ""?

private int GetItemsInCommaSeparatedList(){
    // Locals
    String param = ""; // "1,2,3" returns 3 without issue
    List<String> items = Arrays.asList(param.split("\\s*,\\s*"));

    // Empty?
    if ( items.isEmpty() )
        return 0;

    // Return
    return new items.size();
}

Answer 1

Javadoc to the rescue

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

Your regex doesn't match anything in the empty string and therefore the method returns an array containing one element, your empty string.

Answer 2

Empty string is element as well. Just print content of list.

Answer 3

you are adding empty string to the list.

String param = ""; // "1,2,3" returns 3 without issue
List<String> items = Arrays.asList(param.split("\\s*,\\s*"));

That's why it returns 1 as size

Answer 4

Your split delimiter \\\\s*,\\\\s* does not match the empty string, at the point, the resulting array has just one element, which is the string itself. If you want to return 0 for the empty String, try this:

private static int GetItemsInCommaSeparatedList(){

    String param = ""; // "1,2,3" returns 3 without issue
    Pattern p = Pattern.compile("\\s*,\\s*");
    Matcher m = p.matcher(param);
    List<String> items = new ArrayList<String>();
    if(m.find()){
        System.out.println("Found");
        items = Arrays.asList(param.split("\\s*,\\s*"));
    }

    if ( items.isEmpty() )
        return 0;
    return items.size();
}