Regex \\d* vs \\d\\d

Question

I have this issue with regex.
String s = "10 apples 20 oranges 30 pears";
String regx = "(\\d*\\s[a-z]*)*";
When I use the above pattern in any regular expression code for the given string 's', "10 apples 20 oranges 30 pears" is matched
If I change regx to "(\\d\\d\\s[a-z]*)*" then it matches "10 apples" only.
Why does it happen like this? I know * is zero or more but isn't \\d\\d is same as \\d* in this code?
Thanks

Answer 1

Right. You can see it happening if you remove the outer '*' and step through the matches with find(): import java.util.regex.*;
public class Test
  public static void main(String args[])
    String s = "10 apples 20 oranges 30 pears";
    Pattern p = Pattern.compile("(\\d*\\s[a-z]*)");
    Matcher m = p.matcher(s);
    while (m.find())
      System.out.printf(">%s<%n", m.group(1));
} Because everything else is controlled by asterisks, the regex is only required to match one whitespace character, and on the second and fourth passes, that's what it does: >10 apples<
<
20 oranges<
<
30 pears< In the second version of the regex, you need to allow for the optional trailing space: "(\\d\\d\\s[a-z]+\\s?)+"); In general, when you need to match at least one of something, use '+' instead of '*'. That will help prevent confusing situations like this.