Loop if else in scanner

May 19, 2022

I want to loop my scanner if the user entered something and it made the statement false in my code, if the user entered a false statement, the loop will continue but if I enter the right statement, it will still continue.

Scanner sc = new Scanner(System.in);
    
    System.out.println("Enter your student number: ");
    String sn = sc.nextLine();
    
    String REGEX = "[0-9]{4}.[0-9]{2}.[0-9]{3}";
    Pattern pattern = Pattern.compile(REGEX);      
    Matcher matcher = pattern.matcher(sn);
   
    do {
        if (matcher.matches()) {
            System.out.println("You have succesfully logged in");   
            System.out.println("Hello " + sn + " welcome to your dashboard");   
        }
        else    
            System.out.println("Please enter your student number in this format: 'xxxx-xx-xxx' ");
            System.out.println("Enter your student number: ");
            sc.nextLine();

          
    } while (true);

>Solution :

I would rewrite it like this

Scanner sc = new Scanner(System.in);

System.out.println("Enter your student number: ");
String sn = sc.nextLine();

String REGEX = "[0-9]{4}.[0-9]{2}.[0-9]{3}";
Pattern pattern = Pattern.compile(REGEX);

while(!pattern.matcher(sn).matches()) {
    System.out.println("Please enter your student number in this format: 'xxxx-xx-xxx' ");
    System.out.println("Enter your student number: ");
    sn = sc.nextLine();
}
System.out.println("You have succesfully logged in");
System.out.println("Hello " + sn + " welcome to your dashboard");