Java Scanner with regex delimiter

Question

Why does the following code return false?

Scanner sc = new Scanner(\"-v \");
sc.useDelimiter(\"-[a-zA-Z]\\\\s+\");
System.out.println(sc.hasNext());

Answer 1

Thanks John Kugelman, I think you're right.

Scanner can use customized delimiter to split input into tokens. The default delimiter is a whitespace.

When delimiter doesn't match any input, it'll result all the input as one token:

    Scanner sc = new Scanner("-v");
    sc.useDelimiter( "-[a-zA-Z]\\s+");
     if(sc.hasNext())
          System. out.println(sc.next());

In the code above, the delimiter actually doesn't get any match, all the input "-v" will be the single token. hasNext() means has next token.

    Scanner sc = new Scanner( "-v ");
    sc.useDelimiter( "-[a-zA-Z]\\s+");
     if(sc.hasNext())
          System. out.println(sc.next());

this will match the delimiter, and the split ended up with 0 token, so the hasNext() is false.