If you’re using Java, there’s a high chance you’ve seen its pattern matching before. The String#matches(String) method internally uses the Pattern type, which comprises more complex functionality:
A Pattern is created by compiling a regular expression. The pattern matches any input string and can optionally find capturing groups, which isolate certain parts of your string data.
The API is used as follows:
1 2 3 4 5 6 | Pattern pattern = Pattern.compile("([\\^\\S]+) is powerful");Matcher matcher = pattern.matcher("Java is powerful");System.out.println(matcher.find()); // trueSystem.out.println(matcher.group()); // Java is powerfulSystem.out.println(matcher.group(1)); // Java |
The find() method finds the next occurrence of the pattern, which matches the whole input string in this example. The group() method returns either the whole capturing group, that is, matching the whole pattern, or, when qualified with an index, returns the individual capturing groups. The capturing groups indexes start at 1, not at 0.
There’s also a matches() method which works slightly differently:
1 2 3 4 5 | Pattern pattern = Pattern.compile("([\\^\\S]+) is powerful");Matcher matcher = pattern.matcher("Our Java is powerful");System.out.println(matcher.matches()); // falseSystem.out.println(matcher.find()); // true |
matches() attempts to match the whole input string to the pattern, from start to end, while find() only tries to find the patterns somewhere in the input string.
Also, as reminder: Please use the shortcut methods String#matches(String) or Pattern#matches(String, CharSequence) only for single matching invocations that are not repeated over and over again. Patterns are rather heavy to compile and we should leverage the immutability of the Pattern type and reuse it for multiple matches.
The content of this post was reposted from my newsletter issue 034.
Published on Java Code Geeks with permission by Sebastian Daschner, partner at our JCG program. See the original article here: Matching patterns with Java Opinions expressed by Java Code Geeks contributors are their own. |
Thanks for sharing useful information article and keep us updated on the topic
Hi…
I’m Elena gillbert.Java provides the java.util.regex package for pattern matching with regular expressions. Java regular expressions are very similar to the Perl programming language and very easy to learn. Java regular expressions are very similar to the Perl programming language and very easy to learn.