Question

Basically, my situation requires me to check to see if the String that is defined by user input from the keyboard is only alphabetical characters in one case and only digits in another case. This is written in Java.

my current code:

switch (studentMenu) {
                case 1: // Change all four fields
                    System.out.println("Please enter in a first name: ");

                    String firstNameIntermediate = scan.next();
                    firstName = firstNameIntermediate.substring(0,1).toUpperCase() + firstNameIntermediate.substring(1);
                    System.out.println("Please enter in a middle name");
                    middleName = scan.next();
                    System.out.println("Please enter in a last name");
                    lastName = scan.next();
                    System.out.println("Please enter in an eight digit student ID number");
                    changeID();
                    break;
                case 2: // Change first name
                    System.out.println("Please enter in a first name: ");
                    firstName = scan.next();
                    break;
                case 3: // Change middle name
                    System.out.println("Please enter in a middle name");
                    middleName = scan.next();
                    break;
                case 4: // Change last name
                    System.out.println("Please enter in a last name");
                    lastName = scan.next();
                case 5: // Change student ID:
                    changeID();
                    break;
                case 6: // Exit to main menu
                    menuExit = true;
                default:
                    System.out.println("Please enter a number from 1 to 6");
                    break;
            }
        }
    }

public void changeID() {
    studentID = scan.next();
    }

I need to make sure the StudentID is only numerical and each of the name segments are alphabetical.

Answer 1

java.util.Scanner can already check if the next token is of a given pattern/type with the hasNextXXX methods.

Here’s an example of using boolean hasNext(String pattern) to validate that the next token consists of only letters, using the regular expression [A-Za-z]+:

    Scanner sc = new Scanner(System.in);
    System.out.println("Please enter letters:");
    while (!sc.hasNext("[A-Za-z]+")) {
        System.out.println("Nope, that's not it!");
        sc.next();
    }
    String word = sc.next();
    System.out.println("Thank you! Got " + word);

Here’s an example session:

Please enter letters:
&#@#$
Nope, that's not it!
123
Nope, that's not it!
james bond
Thank you! Got james

To validate that the next token is a number that you can convert to int, use hasNextInt() and then nextInt().

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