How Matcher.find() works [duplicate]

Answer 1

Your expression use * that means 0 or more digit, so can match no digit too.

Change your regular expression in this way

Pattern pattern = Pattern.compile("\\d+");

Using + means 1 or more.

Answer 2

Your regular expression can match zero characters. The final match is a zero width string occurring at the end of the string, after the character at index 5. The index of this zero width string is therefore 6.

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As an aside, you might also find it easier to understand what is going on if you use separators to make the output more readable:

System.out.println(matcher.start()+ ": " + matcher.group());

Results:

0: 
1: 
2: 34
4: 
5: 
6: 

ideone