从客户列表中返回客户

Question

So I have these two methods: The first one is to go through the arraylist of customers and return a value c which is the customer whose ID of type String matches with one of the customers within the ArrayList .

private Customer findCustomer(String id){
    Customer c;
    for(Customer customer : customers){
        if(customer.getID().equals(id)){
            c = customer;
            return c;
        }
    }
    return null;
}

Then I have the second one which when someone access this method in my GUI of a make-shift movie rental program and passes in the movie, the day they are renting, and the id of the customer

public void movieRented(Movie m, Date rented, String id){
    m.setDateRented(rented);
    Customer c = findCustomer(id);
    c.addMovie(m);
    m.setIntStock(false);
}

I am getting an error message surrounding these two methods, and I just wanted to make sure that they at least look correct.

Answer 1

Take care that you are returning null, so you can have a NullPointerException

private Customer findCustomer(String id){
        Customer c;
        for(Customer customer : customers){
            if(customer.getID().equals(id)){
                c = customer;
                return c;
            }
        }
        return null;
    }

You may consider improving your method

private Customer findCustomer(String id){
            Customer c=null;
            for(Customer customer : customers){
                if(customer.getID().equals(id)){
                    c = customer;
                    break;
                }
            }
            return c;
}

Or better now , using custom exceptions

 private Customer findCustomer(String id) throws NoFoundCustomerException{
                Customer c=null;
                for(Customer customer : customers){
                    if(customer.getID().equals(id)){
                        c = customer;
                        break;
                    }
                }
                if(c == null){
                 throw new NoFoundCustomerException();
                }

                return c;
}

And in client code you can do something like this:

public void movieRented(Movie m, Date rented, String id){
    try{
    m.setDateRented(rented);
    Customer c = findCustomer(id);
    c.addMovie(m);
    m.setIntStock(false);
   }catch(NotFoundedCustomerException e){
     JOptionPane.showMessage(null,"Customer doesn't exist");
   }
}

And your exception would look like this

public class NotFoundedCustomerException extends Exception{

 public NotFoundedCustomerException(){
        super();
 }

 public NotFoundedCustomerException(String message){
        super(message);
 }
  .
  .
  .
}

Answer 2

I'm not sure if this is right but there could be a spelling mistake in this line:

m.setIntStock(false);

It looks like is should be

m.setInStock(false);

It also seems that you could be having trouble if the customer is not found you return null. If you are not sure why this is happening I would suggest some simple println statements. For example:

System.out.println("customer id = " + customer.getId() + " id= " + id);