Regular expression in java for validating numbers

Posted by / 28-Aug-2020 08:19

On an abstract level a regular expression, regex for short, is a representation of a set of strings. Instead of having a list and thus the complete set of strings that are valid zip codes, it’s often more practical to have a short and precise regex that completely describes the set. As an example consider the set of strings that end in “.csv”.

The following is a regular expression pattern that represents this set.

This page explains what makes this site special among all other regex sites, but first let's answer a burning question: What is the meaning of life? As per the regex humor page, it's simply matches the position in the string Camel Case where we shift from a lower-case letter to an upper-case letter.

This regex tutorial, one of the most detailed on the web, takes you all the way to mastery.

When I started learning regex, as I was hopping from page to page and book to book, the content was much alike so the "information tree" wasn't yielding all its fruits.

As a result, several questions that cut diagonally through the field of regex were staying unresolved.

What's more, the raw syntax you usually see in code that contains regexes used to intimidate me.

Who wants to deal with a language that looks like this?

Let’s start with a basic question that may present itself if you’ve never worked with regular expressions before.

You also find regex engines ready to roar in most programming languages—such as C#, Python, Perl, PHP, Java, Java Script and Ruby. At this stage, this is a semantic question—it depends on what one means by regular expression. When I was a young dinosaur, I didn't take the time to properly learn the syntax, largely because I really didn't feel like learning another language.

Let's compress the definition from the earlier paragraphs: A regex is a text string that describes a pattern that a regex engine uses in order to find text (or positions) in a body of text, typically for the purposes of validating, finding, replacing or splitting. That topic and other juicy details are discussed on the page about Regex vs. Before we dive in—and only if you have time—I'd like to introduce this site and what makes it special. Who needs regex, I thought, when your programming language has functions that let you dig into strings from the left, the middle and the right?

And you could use the regex to find digits within underscores (as in _12_) and to replace the underscores with double dashes, yielding --12--, something you could not do with a conventional search-and-replace (details for that technique are in the recipe about replacing one delimiter with another).

Who does this work of finding, replacing, splitting? For instance, you can find regex engines in text editors such as Notepad and Edit Pad Pro.

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But if you take your time to read the carefully-built tables on the quick-launch page then perhaps the page about Get ready, because as far as I know, this site is one of the two most comprehensive regex sources on the net—along with Jan Goyvaerts excellent regex tutorial site.