Pattern.matches doesn't work, while replaceAll does

Question

The regular expression seems to be ok, since the first line line correctly replace the substring with "helloworld", but the same expression won't match in the latter since i cannot see "whynothelloworld?" on console

System.out.println(current_tag.replaceAll("^[01][r]\\s", "helloworld"));

if (Pattern.matches("^[01][r]\\s", current_tag)) { System.out.println("whynothelloworld?");}

Answer 1

Pattern.matches() expects the entire string to match, not just a substring.

Use the .find() method of the regex matcher object instead:

Pattern regex = Pattern.compile("^[01]r\\s");
Matcher regexMatcher = regex.matcher(current_tag);
foundMatch = regexMatcher.find();