Question

suppose we have string like jason-458164888

how do we check if the numbers are vaild where the first number should be 4 and length of 9.

use simple program.

Answer 1

// CheckNumbers.java

public class CheckNumbers {

        public static void main(String[] args) {
                
                String s = "jason-458164888";
                
                int countNumbers = 0;
                int firstNum = -1;
                
                int i =0;
                while(i<s.length()) {
                        
                        // checking if character is integer
                        boolean flag = Character.isDigit(s.charAt(i));
                        
                        // if true it is a integer
                        if(flag == true) {
                                // counting numbers
                                countNumbers++;
                                // updating first number 
                                if(firstNum == -1) {
                                        firstNum = Integer.parseInt(String.valueOf(s.charAt(i)));
                                }
                        }                       
                        i++;
                }
                
                // if first number is 4 and counting numbers is 9
                // then print YES else NO
                if(firstNum == 4 && countNumbers == 9 ) {
                        System.out.println("YES");
                }else {
                        System.out.println("NO");
                }
                
        }

}

Code :

Output :