Posix character classes p{ASCII} Java regex.

This class matches the ASCII characters i.e. \x00-\x7F.

Example

 Live Demo

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Example {
   public static void main(String args[]) {
      //Reading String from user
      System.out.println("Enter a string");
      Scanner sc = new Scanner(System.in);
      String input = sc.nextLine();
      //Regular expression
      String regex = "^[\p{ASCII}]";
      //Compiling the regular expression
      Pattern pattern = Pattern.compile(regex);
      //Retrieving the matcher object
      Matcher matcher = pattern.matcher(input);
      int count = 0;
      while(matcher.find()) {
         count++;
      }
      System.out.println("Number of non-ASCII characters in the given string: "+count);
   }
}

Output

Enter a string
why do we fall
Number of non-ASCII characters in the given string: 1