Using regex in Java

Question

I am checking for precedence in a string in my function. Is there a way to change my code to incorporate regex -- I am quite unfamiliar with regex, and though I have read some tutorials online, still not getting 'it' too well. So any guidance would really be appreciated.

For example in a string XLYZ, if the char after X is not L or C, the 'violation' statement gets printed. Here's the code below:

if (subtnString[cnt]=='X' && cnt+1<subtnString.length){
                if(subtnString[cnt+1]!= 'L' || subtnString[cnt+1]!= 'C'){
                    System.out.println("Violation: X can be subtracted from L and C only");
                    return  false;
                }
            }

Is there a way I can use regex to replace this code?

zx81 · Accepted Answer · 2014-06-29 07:10:22Z

6

You can use something like this:

Pattern regex = Pattern.compile("^X[LC]");
Matcher regexMatcher = regex.matcher(subjectString);
if(regexMatcher.find() )  { // it matched!
}
else { // nasty message
     }

In the demo, see the strings that match.

Explanation

The ^ anchor asserts that we are at the beginning of the string
X matches the literal X
[LC] is a character class that matches either one L or one C

Reference

edited Jun 29, 2014 at 7:10

answered Jun 29, 2014 at 7:03

zx81

42k10 gold badges92 silver badges106 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

JB Nizet Over a year ago

Given these explanations, XLYZ doesn't match the regex.

137 Over a year ago

Great answer! The only thing I would add is that you should check tou the Documentation on Strings in Java. You can browse all the methods it provides for working with strings.

JB Nizet Over a year ago

@zx81 yes, we do match the whole string.

Farvardin · Accepted Answer · 2015-05-02 08:44:48Z

1

to match texts that violate your rule use this regex:

X[^LC]

see Demo

and to match regex that do not violate your rule use this:

X[LC]

see Demo

edited May 2, 2015 at 8:44

answered Jun 29, 2014 at 7:09

Farvardin

5,4226 gold badges36 silver badges54 bronze badges

Collectives™ on Stack Overflow

Using regex in Java

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related