About regex

[Abimaran Kugathasan]

Could anyone please explains this code in detail.........

import java.util.Scanner;

public class Test	{
	public static void main(String[] args)	{
		String input = "1 fish 2 fish red fish blue fish";
		Scanner s = new Scanner(input).useDelimiter("\\s*fish\\s*"); // This works...
                //Scanner s = new Scanner(input).useDelimiter("fish"); This won't work.....

		System.out.println(s.nextInt());
		System.out.println(s.nextInt());
		System.out.println(s.next());
		System.out.println(s.next());
		s.close();
	}
}

I couldn't catch up these behaviors..... Any suggestion regarding regex with related to SCJP 6 exam?

Thanks in Advanced~!

[Matthew Brown]

Your line 6 splits the input string into tokens based on a delimiter "any number of spaces (including 0), followed by fish, followed by any number of spaces".

This will split your string as follows: "1/ fish /2/ fish /red/ fish /blue/ fish", which gives you the tokens: "1", "2", "red", "blue".

The commented out line 7 is very similar, but because the delimiter doesn't include spaces, it splits the string as: "1 /fish/ 2 /fish/ red /fish/ blue /fish", which gives you the tokens: "1 ", " 2 ", " red ", " blue ". Note the spaces.

That would work. But then on line 9 you are trying to read the next token as an int. "1" converts to an int with no difficulties. But " 1 " doesn't, so it'll throw an exception using the second delimiter.

Does that explain what you wanted?

[Sandra Bachan]

I haven't studies regex yet, but I modified the code as below:

import java.util.*;
import java.util.Scanner;

public class Fish	{
	public static void main(String[] args)	{
		String input = "1 fish 2 fish red fish blue fish";
		//Scanner s = new Scanner(input).useDelimiter("\\s*fish\\s*"); 
                Scanner s = new Scanner(input).useDelimiter(" fish "); 
		try{
			System.out.println(s.nextInt());
			System.out.println(s.nextInt());
			System.out.println(s.next());
			System.out.println(s.next());
			s.close();
		}
		catch (InputMismatchException im) {
			System.out.println("Input Mismatch");		
		}
	}
}

I get the following output:


1
2
red
blue fish

Why does the last line output blue fish instead of just blue ?

[Samrat Debroy]

@Sandra: Your delimiter is " fish ". Notice the space in the end. Now in the sample string the last fish doesn't have a space in the end.
So, this does not match the delimiter. Thats why it prints "blue fish".
Whereas, if the delimiter is "\\s*fish\\s*" then it will match zero or more space in the end.