Java Regular Expressions

External

• http://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html#sum

Internal

• java
• Regular Expressions

Overview

Regular expressions can be used in Java via the String API or java.util.regex API.

java.util.regex API

The default sequence for using regular expressions consists in building a Pattern instance, which then can be matched against multiple strings by applying it via Matcher instances. The Pattern instance contains a compiled representation of the regular expression. The Matcher uses the Pattern, but encapsulates all the state required to perform matching against a String, so the Pattern can be shared by multiple Matchers. The Matcher instances are not thread safe, see Concurrent Usage Considerations below.

public class Example {

  public static final Pattern PATTERN = Pattern.compile(".*red.*");

  ...

  public void useRegex(String argument) {

      Matcher m = PATTRN.matcher(argument);

      ...

  }

Once built, a Matcher instance can be used to match or find.

Matcher.matches()

The Matcher.matches() method attempts to match the entire input sequence against the pattern.

Matcher.find()

Working code is available here:

https://github.com/NovaOrdis/playground/tree/master/java/regex/simplest

java.langString API

String s = "...";
s.matches(...);

While convenient in some cases, the String API also delegates to the java.util.regex API via the Pattern.matches() call.

Concurrent Usage Considerations

Matcher instances are NOT thread safe, create a matcher per thread