Question

I have a sample string that I want to match: "a123456.java,a12344*javaaaaaaaaaaaaa"

I use the following regex pattern: Pattern p=Pattern.compile("a[0-9]+[.]?[a-zA-Z]+");

Now the ? operator means 0 or more occurrences of ".". Why is the string "a12344*javaaaaaaaaaaaaa" not picked up by this? Why is the * character not counted as a 0 occurrence?

Answer 1

If you mean that you expected the * to be picked up by the . because that means ‘anything’:

Inside the character class, the . becomes a literal ., instead of the character meaning ‘anything’.

If you want to match anything, then use .? instead of [.]?

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If you meant that * is not ., so is zero occurrences of .:

You are right, but in your regex, the . must be followed by a letter ([a-zA-Z]), and the * is obviously not a letter.

To clarify, you have:

a -> "a"
[0-9]+ -> "12344"
[.]? -> ""
[a-zA-Z]+ -> Cannot match "*"