Question

Scanner sc = new Scanner(System.in);
Boolean valid =  true;
do{
    valid = true;
    //get first name input and valid
    System.out.print("Enter your First Name > ");
    String firstName = sc.nextLine();
    if(firstName.trim().length() > 25){
        valid = false;
    }
    //get last name input and valid
    System.out.print("Enter your Last Name > ");
    String lastName = sc.nextLine();
    if(lastName.trim().length() > 25){
        valid = false;
    }
    //get email input and valid
    System.out.print("Enter your Email > ");
    String email = sc.nextLine();
    if(email.trim().length() > 40){
        valid = false;
    }
      ctrl.addPerson(email, firstName, lastName);

}while(valid == false);

User keeps being prompted for invalid input, but invalid data still added/saved (addPerson).
I can understand why invalid is saved, but how should i use the if correctly? thank you for the help!

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I have read everyone’s suggestions and recommendations, below is the editted codes. Hopefully it is better.

Scanner sc = new Scanner(System.in);
boolean valid =  true;
String firstName = null;
String lastName = null;
String email = null;
Date birthday = null;

        do{
            System.out.print("Enter your First Name > ");
            firstName = sc.nextLine();
        }while(firstName.trim().length() > 25);

        do{     
            System.out.print("Enter your Last Name > ");
            lastName = sc.nextLine();
        }while(lastName.trim().length() > 25);

        do{     
            System.out.print("Enter your Email > ");
            email = sc.nextLine();
        }while(email.trim().length() > 40);

        ctrl.addPerson(email, firstName, lastName);

Answer 1

You need to put method addPerson under condition like

if(valid) {
    ctrl.addPerson(email, firstName, lastName);
}

I also suggest you to use primitive types (boolean instead of Boolean), there is no reason to use its object representation here.