This package provides an implementation of regular expression matching based on Russ Cox's linear-time RE2 algorithm.

The API presented by {@code com.google.re2j} mimics that of {@code java.util.regex.Matcher} and {@code java.util.regex.Pattern}. While not identical, they are similar enough that most users can switch implementations simply by changing their {@code import}s.

The syntax of the regular expressions accepted is the same general syntax used by Perl, Python, and other languages. More precisely, it is the syntax accepted by the C++ and Go implementations of RE2 described at https://github.com/google/re2/wiki/Syntax, except for \C (match any byte), which is not supported because in this implementation, the matcher's input is conceptually a stream of Unicode code points, not bytes.

The current API is rather small and intended for compatibility with {@code java.util.regex}, but the underlying implementation supports some additional features, such as the ability to process input character streams encoded as UTF-8 byte arrays. These may be exposed in a future release if there is sufficient interest.

Example use:

    import com.google.re2j.Matcher;
    import com.google.re2j.Pattern;

    Pattern p = Pattern.compile("b(an)*(.)");
    Matcher m = p.matcher("by, band, banana");
    assertTrue(m.lookingAt());

    m.reset();                              // "by, band, banana"
    assertTrue(m.find());
    assertEquals("by", m.group(0));         //  --
    assertEquals(null, m.group(1));         //
    assertEquals("y",  m.group(2));         //   ^
    assertTrue(m.find());
    assertEquals("band", m.group(0));       //      ----
    assertEquals("an",   m.group(1));       //       ^^
    assertEquals("d",    m.group(2));       //         ^
    assertTrue(m.find());
    assertEquals("banana", m.group(0));     //            -------
    assertEquals("an",     m.group(1));     //             ^^
    assertEquals("a",      m.group(2));     //                  ^
    assertFalse(m.find());