Validation.java

package week3_methods;

import java.util.InputMismatchException;
import java.util.Scanner;

public class Validation {

    //Create two scanners
    static Scanner stringScanner = new Scanner(System.in);
    static Scanner numberScanner = new Scanner(System.in);


    public static void main(String[] args) {


        // Test the validation methods

        double computerPrice = doubleInput("What is the price of a computer?");
        System.out.println("Thank you, you entered $" + computerPrice);

        System.out.println("Please enter the price of a cellphone");
        double cellPrice = doubleInput();
        System.out.println("Thank you, you entered $" + cellPrice);


        int numberOfStudents = intInput("How many students in a class?");
        System.out.println("Thank you, you entered " + numberOfStudents);

        System.out.println("Please enter the quantity of cellphones");
        int cellQuantity = intInput();
        System.out.println("Thank you, you entered " + cellQuantity);



        //Close scanners.
        stringScanner.close();
        numberScanner.close();

    }    // This is the end of the main method.


    // A variant of the method below - notice it calls doubleInput with null as the argument
    public static double doubleInput() {
        return doubleInput(null);
    }

    //Takes a question, asks user the question, checks to make sure user enters a double, and
    //then returns that double to the calling method.
    public static double doubleInput(String question) {

        while (true) {
            // If user has provided a question, then print it for the user
            if (question != null) {
                System.out.println(question);
            }

            //Try to read what the user typed, expect it to be a double.
            try {
                // If the input can be read as a double, that double value will be returned
                // This ends the loop, and this method, and control returns to the calling method.
                return numberScanner.nextDouble();

            } // if the input can't be read as a double, then an error will be raised.
            // That error can be 'caught' by this code, and we can print an error message.
            // Since we are inside a while loop, then the loop can repeat and ask the user for input again.
            catch (InputMismatchException ime) {
                System.out.println("Error - please enter a number");
                numberScanner.next();   //Clear any other characters from the Scanner
            }
        }

    }

    // A variant of the method below - notice it calls intInput with null as the argument
    public static int intInput() {
        return intInput(null);
    }

    //Takes a question, asks user the question, checks to make sure user enters an int, and
    //then returns that int to the calling method.
    public static int intInput(String question) {

        while (true) {
            // If user has provided a question, then print it for the user
            if (question != null) {
                System.out.println(question);
            }

            //Try to read what the user typed as an int.
            try {
                // If the input can be read as a int, that int will be returned
                // This ends the loop, and this method, and control returns to the calling method.
                return numberScanner.nextInt();

            } // if the input can't be read as an int, then an error will be raised.
            // For example, if the user enters 'ten' or 1.4 or 123456543454343434, these are not ints, so will cause an error.
            // That error can be 'caught' by this code, and we can print an error message.
            // Since we are inside a while loop, then the loop can repeat and ask the user for input again.
            catch (InputMismatchException ime) {
                System.out.println("Error - please enter an integer number");
                numberScanner.next();   //Clear any other characters from the Scanner
            }
        }

    }
}