Please explain the working of * greedy quantifier

Question

Pattern ptn  = Pattern.compile(\"a*\");
Matcher mtch  = ptn.matcher(\"bbaac\");
if(mtch.find()){
    System.out.println(mtch.group());
}

Output - print

Answer 1

The only thing wrong in your code is that you are not looping over all the found subsequence of the Matcher.

while (mtch.find()) { // <-- not if here
    System.out.println(mtch.group());
}

The pattern "a*" will match two empty Strings before matching "aa" in your String, as it is expected because the * quantifier allows for zero occurrences. However, the + quantifier will not match the empty Strings since it matches one or more occurences (tutorial about quantifiers).

 b b a a c
^ ^  ^  ^ ^   <-- matches for case of *