Regex recompiled in loop (ARCH4073)

Key java.performance.regex-recompiled-in-loop · Severity warning · Category performance

Pattern.compile and String.matches recompile the regex on every call. Inside a loop this recompiles a constant pattern repeatedly, incurring noticeable cost.

Incorrect

for (String line : lines) {
    if (Pattern.compile("\\d{4}-\\d{2}").matcher(line).find()) {
        accept(line);
    }
}

Correct

Pattern pattern = Pattern.compile("\\d{4}-\\d{2}");
for (String line : lines) {
    if (pattern.matcher(line).find()) {
        accept(line);
    }
}

Fix

Compile the Pattern once outside the loop and reuse it across iterations.