Create command

Question

The Cashier class is responsible for processessing commands input by the user. There
should be a single field, used to hold all the accounts that the cashier has created, which
has the datatype HashMap. Remember that each entry added to a HashMap requires a key
and a value. In this case, the key will be a String value which is the email address of the
account. The value will be the Account object itself.
You need to write a single constructor for Cashier which initialises the field to an empty
HashMap
import java.util.HashMap;
public class Cashier
    HashMap<String, Accounts> userAccounts;
    Cashier()
        userAccounts = new HashMap<String, Accounts>();
}I have created the single constructor for the HashMap, but I'm totally lost on the next step, any help will be appreciated:
The next step is to make a command called create.
The create command creates a new account. The cashier must ask for an email
address and a password before constructing a new Account object and adding it
to the HashMap of accounts. The cashier responds with ?Your account has been
created?. If an account using the given email address already exists, the cashier
responds with ?The account already exists?.

Answer 1

Read about maps:
http://java.sun.com/docs/books/tutorial/collections/index.html
Especially:
http://java.sun.com/docs/books/tutorial/collections/interfaces/map.html
http://java.sun.com/docs/books/tutorial/collections/implementations/map.html