ArrayList-可以读出元素名称吗？

Question

Heyho everyone!

My project is a bit bigger so I decided to short it a bit and showing only the problem code, which i have currently. On the first, im programming on a console. Reading six strings from a Scanner, before I save them in a variable i'm doing a validity check (length, special signs, etc...). So I decided to make this in an extra method check_newCustomer(). I used an ArrayList to return more as one value. So now is the point that I need the captured inputs in the main() function or any other method which writes the new Customer in the database. Problem is now i don't know how I can reference to userID, firstname, secondname... in other method. I just can refer with an index. But I would prefer it when i can use the variable names to refer to it. So its much easier on the other methods to handle with strings. Possible?

public static void main(String[] args) {
    ArrayList<String> newCustomer = new ArrayList<String>(); 
    check_newCustomer (newCustomer);
}


public static void check_newCustomer(ArrayList<String> newCustomer) throws IOException {
    String userID = null;
    String firstname = null;
    String secondname = null;
    String street = null;
    String zipcode = null;
    String city = null;

    // validity check before I fill the input fields
    ...

    // fill arraylist
    newCustomer.add(userID);
    newCustomer.add(firstname);
    newCustomer.add(secondname);
    newCustomer.add(street);
    newCustomer.add(zipcode);
    newCustomer.add(village);
}

Thanks!

Answer 1

No, the value in the ArrayList is just a reference. The fact that you originally referred to it using a different variable is irrelevant.

You could use a Map<String, String> instead... but it would be much cleaner to have a Customer class which had fields for the various pieces of information. If you want multiple customers, you can then have a List<Customer> .

Answer 2

One needs to make a class Customer, just a group of fields. Instead of a list of Strings.

public class Customer {
    String userID;
    String firstname;
    String secondname;
    String street;
    String zipcode;
    String city;
}

And in the code:

Customer newCustomer = new Customer();
newCustomer.userID = ....
System.out.println(newCustomer.userID);

Answer 3

When you pass check_newCustomer (newCustomer); you are only passing a copy of the array list. In this case, the original array list newcustomer is left intact while a new copy whose scope is within the method check_newCustomer is where all the strings are stored. You can either create a new class for Customers or you can create a class and have your array list as a class variable and check_newCustomer as a class method. In the latter case, it is much simple.

    class customer
        ArrayList<String> newCustomer;
        public static void main(String[] args) {

                newCustomer = new ArrayList<String>(); 
                check_newCustomer ();
            }


        public static void check_newCustomer() throws IOException {
                String userID = null;
                String firstname = null;
                String secondname = null;
                String street = null;
                String zipcode = null;
                String city = null;

                // validity check before I fill the input fields
                ...

                // fill arraylist
                newCustomer.add(userID);
                newCustomer.add(firstname);
                newCustomer.add(secondname);
                newCustomer.add(street);
                newCustomer.add(zipcode);
                newCustomer.add(village);
                }
}

This must work.