Question

<Java Programming>

as mentioned in the text, a java identifier consists of one or more characters. The first character must be an uppercase or lowercase letter of the alphabet, an underscore _, or a dollar sign $. Each remaining character must be an upper case or lowercase letter of the alphabet. a digit 0-9, an underscore, or a dollar sigh. Write a Java program that reads in a line of characters and prints out whether the line of characters is a legal Java Identifier.

Answer 1

import java.util.Scanner;

public class IdentifierValidation {

   public static boolean isValid(String str) {

       // If first character is invalid
       if (!((str.charAt(0) >= 'a' && str.charAt(0) <= 'z') || (str.charAt(0) >= 'A' && str.charAt(1) <= 'Z')
               || str.charAt(0) == '_' || str.charAt(0) == '$'))
           return false;

       // iterating the rest of chars to check
       for (int i = 1; i < str.length(); i++) {
           if (!((str.charAt(i) >= 'a' && str.charAt(i) <= 'z') || (str.charAt(i) >= 'A' && str.charAt(i) <= 'Z')
                   || (str.charAt(i) >= '0' && str.charAt(i) <= '9') || str.charAt(i) == '_'))
               return false;
       }

       return true;
   }

   // Driver code
   public static void main(String args[]) {
       Scanner sc = new Scanner(System.in);
       System.out.println("Enter identifier: ");
       String str = sc.next();
       sc.close();
       if (isValid(str))
           System.out.println(str + " is valid");
       else
           System.out.println(str + " is not valid ");
   }
}

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