Overloading Java function with List<> parameter

Question

I have 2 classes

public class Customer{
  ...
  public String getCustomerNumber();
  ...
}

public class Applicant{
   ....
   private Customer c;
   public Customer getCustomer(){ return c; }
   ...
}

When presented with a list of customers or applicants I want a function which iterates the list and does something with the CustomerNumber.

I've tried overloading the function

public void processCustomerNumbers(List<Customer> custList)
...

public void processCustomerNumbers(List<Applicant> appList)
...

but these are seen as duplicate methods... is there a nice way of doing this rather than just having 2 differently named functions?

Answer 1

If you make both classes implement a common interface,

interface CustomerNumber {
    String getCustomerNumber();
}

public class Customer implements CustomerNumber {
  ...
  public String getCustomerNumber();
  ...
}

public class Applicant implements CustomerNumber {
   ....
   private Customer c;
   public Customer getCustomer() { return c; }
   public String getCustomerNumber() { return getCustomer().getCustomerNumber(); }
   ...
}

then you might be able to do what you want with just a single method:

public void processCustomerNumbers(List<? extends CustomerNumber> appList) {
    for (Customer c: appList) {
        processCustomerNumber(c.getCustomerNumber());
    }
}