Java Regular Expression Tester
Test Java regular expressions (java.util.regex) against any input, highlight all matches, and try replaceFirst / replaceAll.
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How this tester works
Browsers do not ship a Java virtual machine, so this page translates your java.util.regex pattern into an equivalent JavaScript RegExp and runs it locally. Java-only constructs are converted exactly. When a construct has no JavaScript equivalent, the result panel lists the approximations.
Java vs JavaScript regex differences
| Feature | Java | JavaScript |
|---|---|---|
| Pattern in source code | String literal, backslashes doubled | Regex literal or new RegExp() |
| Whole-input match | matcher.matches() |
Anchor with ^...$ |
| Possessive quantifiers | Supported (a*+) |
Not supported (approximated as greedy) |
| POSIX classes | Supported (ASCII) | Not supported |
| Unicode properties | Scripts, blocks, categories | Scripts, categories with u flag |
| Lookbehind | Bounded length only | Unbounded |
Flags
| Flag | Inline | Effect |
|---|---|---|
| CASE_INSENSITIVE | (?i) |
Case-insensitive matching |
| MULTILINE | (?m) |
^ and $ match at line boundaries |
| DOTALL | (?s) |
. also matches line terminators |
| COMMENTS | (?x) |
Whitespace is ignored, # starts a comment |