Confusing output from String.split

Question

I do not understand the output of this code:

public class StringDemo{              
    public static void main(String args[]) {
        String blank = \"\";         


        

Answer 1

We can take a look into the source code of java.util.regex.Pattern which is behind String.split. Way down the rabbit hole the method

public String[] split(CharSequence input, int limit)

is invoked.

Input ""

For input "" this method is called as

String[] parts = split("", 0);

The intersting part of this method is:

  int index = 0;
  boolean matchLimited = limit > 0;
  ArrayList matchList = new ArrayList<>();
  Matcher m = matcher(input);

  while(m.find()) {
    // Tichodroma: this will not happen for our input
  }

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

And that is what happens: new String[] {input.toString()} is returned.

Input ","

For input ","the intersting part is

    // Construct result
    int resultSize = matchList.size();
    if (limit == 0)
        while (resultSize > 0 && matchList.get(resultSize-1).equals(""))
            resultSize--;
    String[] result = new String[resultSize];
    return matchList.subList(0, resultSize).toArray(result);

Here resultSize == 0 and limit == 0 so new String[0] is returned.