Questions from K&B 6

[Kapil Shardha]

I am not able to understand the reason behind the answer for Qs 1 in Self Test for Chapter 6 in K&B's book for SCJP 6

    
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


Moreover, the answer to question 2 of same test is also not clear. Any explanation to these two questions will be of great help.

[Christophe Verré]

Hi Kapil,
Maybe this FAQ will help you understand the problem.

[Jeanne Boyarsky]

Kapil,
Welcome to JavaRanch!

That code matches 0 or more digits. The regular expression tries to find a match as soon as it can. So it thinks something like this.
Position 0 - finds a letter (a). Yup - that's zero digits.
Position 1 - Another letter (b). Great - zero digits.
Position 2 - Ooh - a number. Let's keep looking. Two digits. Outputs "34" and skips outputting the index for the third position since it already matched the "4"
Position 4 - Another letter (e) - Zero digits
Position 5 - Another letter (f) - Zero digits
Position 6 - "End of string" - Yup - zero digits

Kapil Shardha wrote:Moreover, the answer to question 2 of same test is also not clear. Any explanation to these two questions will be of great help.

Can you share question 2 (or a shorter version of it) ? I have the SCJP 5 book (not 6 so things may have changed.) My question #2 deals with Serializable not regular expressions. If you have a question about Serializable, you want to start a new thread. You'll also want to share what your specific doubt is as that isn't a question that can be traced/diagrammed.

[Jeanne Boyarsky]

And clearly I should have looked at the FAQ before typing this. I like reg exps .

[Ankit Garg]

Kapil please Use Code Tags when you post a source code. Edit your message using button and then add code tags to it...

[Kapil Shardha]

Here is the question 2 from Self test of Chapter 6:

    

import java.io.*;
class Player {
Player() { System.out.print("p"); }
}
class CardPlayer extends Player implements Serializable {
CardPlayer() { System.out.print("c"); }
public static void main(String[] args) {
CardPlayer c1 = new CardPlayer();
try {
FileOutputStream fos = new FileOutputStream("play.txt");
ObjectOutputStream os = new ObjectOutputStream(fos);
os.writeObject(c1);
os.close();
FileInputStream fis = new FileInputStream("play.txt");
ObjectInputStream is = new ObjectInputStream(fis);
CardPlayer c2 = (CardPlayer) is.readObject();
is.close();
} catch (Exception x ) { }
}
}

And its answer is "PCP" which is not clear.

[Nitish Bangera]

 CardPlayer c1 = new CardPlayer();    

the CardPlayer's and Player's constructor will run printing PC.

CardPlayer is serializable while Player isn't. So while deserializing, Player's constructor will run printing P

Hence PCP.