Skip to Main Content
Java Cookbook
book

Java Cookbook

by Ian F. Darwin
June 2001
Intermediate to advanced content levelIntermediate to advanced
888 pages
21h 1m
English
O'Reilly Media, Inc.
Content preview from Java Cookbook

Finding the Matching Text

Problem

You need to find the text that matched the RE.

Solution

Sometimes you need to know more than just whether an RE matched an input string. In editors and many other tools, you will want to know exactly what characters were matched. Remember that with multipliers such as * , the length of the text that was matched may have no relationship to the length of the pattern that matched it. Do not underestimate the mighty .*, which will happily match thousands or millions of characters if allowed to. As you can see from looking at the API, you can find out whether a given match succeeds just by using match( ), as we’ve done up to now. But it may be more useful to get a description of what it matched by using one of the getParen( ) methods.

The notion of parentheses is central to RE processing. REs may be nested to any level of complexity. The getParen( ) methods let you retrieve whatever matched at a given parenthesis level. If you haven’t used any explicit parens, you can just treat whatever matched as “level zero.” For example:

// Part of REmatch.java
String patt = "Q[^u]\\d+\\.";
RE r = new RE(patt);
String line = "Order QT300. Now!";
if (r.match(line)) {
    System.out.println(patt + " matches '" +
        r.getParen(0) +
        "' in '" + line + "'"); Match whence = RE.match(patt, line); 
}

When run, this prints:

Q[^u]\d+\. matches "QT300." in "Order QT300. Now!"

It is also possible to get the starting and ending indexes and the length of the text that the pattern matched ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

Practical Cloud-Native Java Development with MicroProfile

Practical Cloud-Native Java Development with MicroProfile

Emily Jiang, Andrew McCright, John Alcorn, David Chan, Alasdair Nottingham
Distributed Computing in Java 9

Distributed Computing in Java 9

Raja Malleswara Rao Malleswara Rao Pattamsetti

Publisher Resources

ISBN: 0596001703Supplemental ContentCatalog PageErrata