Need help in removing trailing and leading zeroes using regex

[Rrohit rakesh upadhyay]

I wrote the following program to remove leading and trailing zeroes from a string using regex.

import java.util.regex.*

class Ragx{
public static void main(String[] args){
 String s=null;
Pattern p= Pattern.compile("([^0])*(\\d)+([^0])*");
Matcher m = p.matcher("00012345000");
System.out.println(m.matches());
while(m.find()){
s=m.group();
}
System.out.println(s);
}
}

Without the 8th line, the output is

00012345000

And with it the output is.

true
null

I do not understant why the string becomes null in the second case even when m.matches() returns true. I think that the pattern says, "match zero or more occurances of a character that is not zero, then match one or more occurances of any digit and again match zero or more occurances of a character that is not zero". If I am wrong then please tell me the right way to do it.

[Henry Wong]

In the first case, you are finding from the beginning. In the second case, you are finding from where the matches() method left off. If you want to (from your loop) use the find() method from the beginning of the string, then don't forget to reset the matcher.

Henry

[Rrohit rakesh upadhyay]

Thank you, Henry. It is the right way to remove leading and trailing zeroes, right?

[Henry Wong]

Rrohit rakesh upadhyay wrote:Thank you, Henry. It is the right way to remove leading and trailing zeroes, right?

Considering that you got a result of "00012345000", which has both leading and trailing zeroes... I would say "no". Your technique didn't work.

Henry

[Rrohit rakesh upadhyay]

When i remove '*' with '+' i am getting the result right but the m.matches() returns false.

[Henry Wong]

Rrohit rakesh upadhyay wrote:When i remove '*' with '+' i am getting the result right but the m.matches() returns false.

Yeah. I think you will need to provide more context ... TellTheDetails.

Henry

[Knute Snortum]

I don't know if we still are supposed to post hints instead of full solutions since this is now in Java in General, but I will say that I have a one-line solution that I will post if I get the go-ahead. Until then, think about using the method replaceFirst(). It's a little confusing because of the "first" in the name, but it's a way to use a regex to replace something in a string ("first" because it replaces only the first instance of it, but we don't care).

[Knute Snortum]

Okay, here's the code I would use to strip off trailing and leading zeros:

String num = "00000123400000";
String newNum = num.replaceFirst("^0*", "").replaceFirst("0*$", "");

[Henry Wong]

Alternatively, the replaceAll() method can also be used, with a merged regex (using the alternation operator).

Henry