Pattern numPat    = Pattern.compile( "(\\d)(\\w?)(\\d)"  );    
String response = "79";
Matcher numMatch  = numPat.matcher( response ); 
if ( numMatch.matches() )
{
  System.out.print  ("1:" + numMatch.group(1) + ", ");   
  System.out.print  ("2:" + numMatch.group(2) + ", " );   
  System.out.println("3:" + numMatch.group(3) );   
}
else
  System.out.println("No Match." );   
}

Answer:

1:7, 2:, 3:9

Group 2 successfully matched the empty string ( the string that contains no characters ), so no characters were printed between 2: and the following comma.

Three-digit Game

Here is a (somewhat lame) game, that asks the user to enter a three-digit number where the digits add up to a randomly selected sum. For example, if the sum is 23, the number could be 995. Appropriate messages are written if the user is wrong or does not enter a three digit number.

import java.util.regex.*;
import java.util.*;

public class ThreeDigitSumGame
{
  public static void main(String[] args)
  {
    Random rand = new Random();  
    int target  = rand.nextInt( 28 );   
    System.out.print("Enter a three-digit number ");
    System.out.print("where the digits add up to " + target + ": " );
    
    Scanner scan = new Scanner( System.in );      
    String response = scan.nextLine();
    
    Pattern numPat = Pattern.compile( "(\\d)(\\d)(\\d)"  );    
    Matcher numMatch  = numPat.matcher( response ); 
    
    if ( numMatch.matches() )
    {
      int numA = Integer.parseInt( numMatch.group(1) );  
      int numB = Integer.parseInt( numMatch.group(2) );  
      int numC = Integer.parseInt( numMatch.group(3) );  
      
      if ( numA+numB+numC == target )
        System.out.println("Correct!" );  
      else
        System.out.println("wrong" );  
    }
    else
      System.out.println("You did not enter a three-digit number." );   
  }
}

QUESTION 11:

Would

int numA = numMatch.group(1) ;

work correctly in this program?