one to one relationship between classes in java

Question

I have to implement following classes in Java SE but I cannot figure out that how can I achieve the one-to-one relationship between ATMCard and Account. I have researched (may be with wrong keywords) but could not find anything. Thank you in advance..

Answer 1

First, I find your model a bit strange for ATMCard and Account:

• isn't the PIN related to the ATMCard rather than to the Account?
• isn't the custName related the Account ?

Then, the 1-1 relationship means you will have one of these:

• the Account class has a member of type ATMCard
• the ATMCard class has a member of type Account
• both above relations.
• none of the above, but getters that will fetch the related entity based on an ID. For instance, you can have a ATMCard$getAccount() that will retrieve the related Account based on the accountNo.

It really depends on the model logic you need.

As @NickHolt suggests, I would go for a one-way relation ship you can initialise through a factory, e.g.

public static ATMCard createCard(String name, int accNo, int pin, int initBal) {
   Account acc = new Account(name, accNo, initBal);
   ATMCard card = new ATMCard(pin);
   card.setAccount(acc);
   return card; 
}

You can have ATMCard and Account constructors protected to enforce the use of the public factory method.

Note: you can use a framework like Spring or Guice to provide this kind of factory and injection service.