CODEWITHSUNDEEP
javaregex
Balconsky
Balconsky

Reputation: 2244

Java regex in scanner

I know it is simple, but I do not know why it does not work.

I try to check if next String in scanner is matched by the pattern: String should begins with

" DESCRIPTION". So, I try:

Scanner sc = new Scanner("   DESCRIPTION = 'Header for scroller'");
System.out.println("Has Next = " + sc.hasNext("\\s+DESCRIPTION.*"));

but it does not work, why? Simpler regex works fine:

 Scanner sc = new Scanner("   DESCRIPTION = 'Заголовки таблиц скроллеров'");
 System.out.println("Has Next = " + sc.hasNext(".*DESCRIPTION.*"));

Upvotes: 2

Views: 1410

Answers (5)

Wirus
Wirus

Reputation: 1190

This doesn't work for you because Scanner uses whitespace as a default delimiter. Thus hasNext cannot find \s+DESCRIPTION and finds .*DESCRIPTION.* or just DESCRIPTION.*. If you would have changed your code to 

Scanner sc = new Scanner("   DESCRIPTION = 'Header for scroller'");
sc.useDelimiter( "_" );
System.out.println("Has Next = " + sc.hasNext("\\s+DESCRIPTION.*"));

then you would have expected result.

Upvotes: 0

boxed__l
boxed__l

Reputation: 1336

Its because the default delimiter pattern for scanner is \p{javaWhitespace}+

Hence the next token becomes DESCRIPTION rather than <space><space>DESCRIPTION

Upvotes: 0

arshajii
arshajii

Reputation: 129507

sc.hasNext(pattern) returns true if the next token matches pattern.

The next token here is "DESCRIPTION".

  • "DESCRIPTION" matches .*DESCRIPTION.*
  • "DESCRIPTION" does not match \s+DESCRIPTION.* (since there are no spaces before the token)

You could try this:

Scanner sc = new Scanner("   DESCRIPTION = 'Header for scroller'");
System.out.println("Has Next = " + sc.hasNext("DESCRIPTION.*"));

Has Next = true

Upvotes: 2

Andr&#225;s Hummer
Andr&#225;s Hummer

Reputation: 972

Perhaps not what you're looking for, but

Scanner sc = new Scanner("   DESCRIPTION = 'Header for scroller'".trim());
System.out.println("Has Next = " + sc.hasNext("^DESCRIPTION.*"));

did the trick for me...

Upvotes: 0

jlordo
jlordo

Reputation: 37813

From JavaDoc of Scanner#hasNext(String pattern)

Returns true if the next token matches the pattern constructed from the specified string

So

sc.hasNext("\\s+DESCRIPTION.*")

returns false because the next token is DESCRIPTION (without any whitespace) and

sc.hasNext(".*DESCRIPTION.*")

returns true because both of the .* match 0 characters before and after DESCRIPTION.

Upvotes: 1

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