Write a regular expression that matches lines that only cont

Write a regular expression that matches lines that only contain a number between 20 and 29 (inclusive).

Solution

import java.util.Scanner;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

import org.apache.commons.lang.math.NumberUtils;

public class UserInputNumInRangeWRegex {

public static final void main(String[] ignored) {

    int num = 20;

    boolean isNum = false;

    int iRangeMax = 29;

   //\"\": Dummy string, to reuse matcher

/** Regular expression between numericals 20 and 29 **/

Matcher mtchrNumNegThrPos = Pattern.compile(\\b(?:20|29)\\b\").matcher(\"\");

do {

         System.out.print(\"Enter a number between \" + num + \" and \" iRangeMax + \": \");

         String strInput = (new Scanner(System.in)).next();

         if(!NumberUtils.isNumber(strInput)) {

              System.out.println(\"Not a number. Try again.\");

         }

        else if(!mtchrNumNegThrPos.reset(strInput).matches()) {

            System.out.println(\"Not in range. Try again.\");

        }

       else {

            //Safe to convert

            num = Integer.parseInt(strInput);

            isNum = true;

       }while(!isNum);

      System.out.println(\"Number: \" + num);

   }

}

Output:

Enter a number between 20 and 29: tuhet
Not a number. Try again.
Enter a number between 20 and 29: 283837483
Not in range. Try again.
Enter a number between 20 and 29: -200000
Not in range. Try again.
Enter a number between 20 and 29: 27
Number: 27