Class Pattern - regular expressions

[Dar Var]

Hi
I have a few regular expressions that each work seperately i.e. each find the strings that contain the its pattern. However I want to create an expression that is a combination of them all. Thus this new totalPattern will check if the string contains % at the beginning or end
but does not contain \% at the end

//finds % at the beginning of the input line
Pattern pattern1 = Pattern.compile("^%"); 
 
//finds % at the end of the input line
Pattern pattern2 = Pattern.compile("%$"); //finds % at the end of the input line
 
//finds \% at the end of the input line
Pattern pattern3 = Pattern.compile("\\\\%$"); 
 
Pattern totalPattern = Pattern.compile(????????combination of above excpressions????????);
 
String[] lines = {"%", "test%", "%test", "test%test", "test\\%"};
 
for (int index = 0; index < lines.length; index++)
        {
            Matcher matcher = totalPattern.matcher(lines[index]);
 
            if(matcher.find())
            {
                System.out.println(lines[index]);
            }
        }

Therefore the code will output:

%
test%
%test

[James Sabre]

Looks like you 'borrowed' one of my other regex posts! I think the following does what you want

 
import java.util.regex.*;
 
public class Fred
{
    private static final Pattern pattern = Pattern.compile("^(%.*(?<!\\\\%))|(.*(?<!\\\\)%)$");
    
    public static void main(String[] args)
    {
        String[] lines = {"%", "test%", "%test", "test%test", "test\\%", "%test\\%"};
        
        for (int index = 0; index < lines.length; index++)
        {
            Matcher matcher = pattern.matcher(lines[index]);
            
            if(matcher.matches())
            {
                System.out.println(lines[index]);
            }
        }
    }
} 

[Dar Var]

Thanks James,
Borrowed that alright! Good stuff.

Can you tell me what book or site you used to learn this?

[James Sabre]

Can you tell me what book or site you used to learn this?

1) Mastering Regular Expression, Jeffrey E. F. Friedl, published by O'Reilly.

My copy is a bit dated now and does not contain topics such as 'negative look behind'. I know there is a new edition but I don't know if it contains 'negative look behind'.

2) Programming Perl, Wall, Christiansen & Schwartz, published by O'Reilly.

I cut my teeth on this when I first learned Perl and Perl without regex is a eunuch.

3) The Javadoc for java.util.regex.Pattern.

4) The SUN Java developer forums where regex questions come up fairly frequently. Each time I find a regex problem posted that I can't deal with I study the responses and make sure I understand them.

5) Google for the various regex tutorials.

[Alan Moore]

Also, there's a good tutorial at

http://www.regular-expressions.info/

The second edition of Friedl's book does cover negative lookbehind, plus other new goodies like atomic groups and possessive quantifiers. And it has a chapter devoted to Java.