java regular expressions: performance and alternative

Question

Recently I have been had to search a number of string values to see which one matches a certain pattern. Neither the number of string values nor the pattern itself is clear

Answer 1

Regular expressions in Java are compiled into an internal data structure. This compilation is the time-consuming process. Each time you invoke the method String.matches(String regex), the specified regular expression is compiled again.

So you should compile your regular expression only once and reuse it:

Pattern pattern = Pattern.compile(regexPattern);
for(String value : values) {
    Matcher matcher = pattern.matcher(value);
    if (matcher.matches()) {
        // your code here
    }
}