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java regex

Posted on 2013-11-19
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Last Modified: 2013-11-25
Hi,

I was going through below link

http://www.tutorialspoint.com/java/java_regular_expressions.htm

Does java java regular expresssion is part of new java release or is it there from long time.

why we use regular expression. What are advantages, disadvantages, practical uses, alternative ways to it.

please advise
Any links resources ideas highly appreciated. Thanks in advance
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Question by:gudii9
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dpearson earned 250 total points
ID: 39661414
Java regular expressions have been in the language since version 1.4 (a long time ago now).

You can see this for any Java class by looking in the docs:
http://docs.oracle.com/javase/7/docs/api/java/util/regex/Matcher.html

Has a line:

Since:
1.4

which shows when it was added to the Java language.

Regular expressions are used when matching patterns in strings.  That comes up a lot in programming - e.g. making sure that a phone number follows the pattern:

(nnn) nnn-nnnn

can be easily checked with a regular expression.

They are also very fast when doing operations like scanning a big document for a specific pattern (e.g. find the first place where "Thanks" occurs before "advance" in a web page).

Much faster than code you would write yourself to do this - by perhaps getting the first character of the page, see if it's a "T".  If not, get the next character etc.

So they are good things to learn and use.

Doug
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by:mccarl
mccarl earned 250 total points
ID: 39661419
Does java java regular expresssion is part of new java release or is it there from long time
A quick read of the Javadoc for the java.util.regex package says that the package and the classes within have been available since Java v1.4

http://docs.oracle.com/javase/7/docs/api/java/util/regex/package-summary.html

why we use regular expression
To allow quite flexible and potentially complex matching operations on a sequence of characters. And can also be used to perform replacement of found matches and possibly capture and return some part(s) of the found match. And plenty of other uses, I'm sure.
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by:mccarl
ID: 39661424
I type too slowly! Sorry Doug, I didn't refresh the page before posting :)
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by:dpearson
ID: 39661447
Haha - great minds think alike mccarl!

Doug
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by:gudii9
ID: 39670090
They are also very fast when doing operations like scanning a big document for a specific pattern (e.g. find the first place where "Thanks" occurs before "advance" in a web page).

I have not understood this use case. what is the meaning of 'Thanks' occurs before "advance".

Please advise
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by:dpearson
ID: 39670870
I have not understood this use case. what is the meaning of 'Thanks' occurs before "advance".

It was just an example - searching for the word "Thanks" occurring somewhere in a document before the word "advance"

Thanks for helping.    // No match
Thanks in advance.    // Match - but notice how the words aren't next to each other

It's not that easy to write code to do this yourself.  But regular expressions handle it really well.

Doug
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