Chapter 6 Self Test Q1

[sapana jain]

import java.util.regex.*;
class Regex2
{
public static void main(String[] args)
{
Pattern p = Pattern.compile(args[0]);
Matcher m = p.matcher(args[1]);
boolean b = false;
while(b = m.find())
{
System.out.print(m.start() + m.group());
}
}
}
And the command line:
java Regex2 "\d*" ab34ef

What is the result?
A. 234
B. 334
C. 2334
D. 0123456
E. 01234456
F. 12334567
G. Compilation fails.

Answer is E but i am not getting this please explain me.

[sridhar row]

check this out FAQ

[Thirugnanam Saravanan]

The pattern "\d*" will look for 0 to many digits in the String.

The String given in the question is ab34ef

AS you must be aware of,Whenever the JVM finds the start() method it will display the starting index of the matching digit and whenever it finds group() method it will display the corresponding digit(s) found in the starting index.

In this particular case, the matching occurs as follows:

m.start() m.group()
--------------------------------------
0 no matching digit(s) satisfying "\d*"
1 no matching digit(s) satisfying "\d*"
2 34
3 already consumed in the previous match for "\d*"
4 no matching digit(s) satisfying "\d*"
5 no matching digit(s) satisfying "\d*"
6 no matching digit(s) satisfying "\d*"

combining this in m.start() + m.group for all the iterations we get as

01234456
[ May 09, 2008: Message edited by: Thirugnanam Saravanan ]

[sapana jain]

thanks for helping me.Now the whole concept is clear to me.Question are really very tough.

[Aaron Browne]

Hi guys, what I don't get is where index 6 has come from:

0 no matching digit(s) satisfying "\d*" (a)
1 no matching digit(s) satisfying "\d*" (b)
2 34 (34)
3 (already consumed)
4 no matching digit(s) satisfying "\d*" (e)
5 no matching digit(s) satisfying "\d*" (f)
6 no matching digit(s) satisfying "\d*" (???)

[Ulf Dittmer]

Aaron, did you read the FAQ entry sridhar linked to?

[Aaron Browne]

My bad; :roll:
Cheers