What is wrong with the regex?

[Joe Harry]

I have to look out for the ouucrences of a particular sequence which is a &# followed by numbers (0 to 9) and ends with a semicolon.

 For example., & # 123 ; or  &# 12345;

I have defined the following as my regex expression, but it never matches.

"&#[0-9];"

I'm sure that I made a mistake. But not sure where.

[Matthew Brown]

That will only match a single number. You need [0-9]+ to match any number.

[Joe Harry]

Evwn this would return flase when I tried with the following string:

Regex used - &#[0-9]+;
Test String  - &# 123;yxc&# 251;123;

[Wouter Oet]

There is a space in your test String but your regex doesn't allow that.

[Joe Harry]

The space is because I do not know how to make it look proper in my post above. If I do not leave a space and post it here, it gets shown up as its original character. You can take it as such that there is no space in my regex.

[Wouter Oet]

Then it matches. You can test it with the regex test harness. It will return that it finds 2 groups.

[Joe Harry]

I tried the following:

		Pattern pat = Pattern.compile("&#[0-9]+;");
		Matcher mat = pat.matcher("&# 123;yxc&# 251;123;");
		System.out.println(mat.matches()); // always prints false

[James Sabre]

Joe Harry wrote:I tried the following:

		Pattern pat = Pattern.compile("&#[0-9]+;");
		Matcher mat = pat.matcher("&# 123;yxc&# 251;123;");
		System.out.println(mat.matches()); // always prints false

Matcher.matches() requires the whole string to match. You need Matcher.find() . Check the Javadoc for Matcher.

[Joe Harry]

Matcher.find() prints me true. But is there a way to extract the groups? I need those sequences as an array for checking against a predefined list. I tried mat.groupCount() and it gave me 0.

[James Sabre]

Joe Harry wrote:Matcher.find() prints me true. But is there a way to extract the groups? I need those sequences as an array for checking against a predefined list. I tried mat.groupCount() and it gave me 0.

while (mat.find())
{
    String value = mat.group(); // Extracts everything that matched
}

If you only want the decimal part then put brackets '( and ') round the [0-9]+ and use mat.group(1) .

You will keep banging your head until you spend some time learning about regular expression and Java's Pattern and Matcher classes.

[Wouter Oet]

And did you check out the link I provided?

[Joe Harry]

Thanks for the suggestion. But when I tried mat.group(0), it gave me the following:

Exception in thread "main" java.lang.IllegalStateException: No match found 

But when I loop through using the find(), it prints the matched elements.

[Joe Harry]

Wouter Oet wrote:And did you check out the link I provided?

Oh, yes. I just did. Thanks for all the help!

[James Sabre]

Joe Harry wrote:Thanks for the suggestion. But when I tried mat.group(0), it gave me the following:

Exception in thread "main" java.lang.IllegalStateException: No match found 

But when I loop through using the find(), it prints the matched elements.

But that is what my code fragment showed you had to do!