Java Quiz 15: Improve Encapsulation of Your Code

Before we start with this week's puzzle, here is the answer to Java Quiz 14: Overloading Methods.

The method writeValue(1, 2) invokes writeValue(int, int) because 1 and 2 are integers.
The method writeValue(int, int) doesn't exist. Therefore, writeValue(int, double)
is invoked instead of writeValue(int, Integer). The reason is that widening is preferred over boxing/unboxing. The correct answer is: D.

Here is the Java puzzle for today!

If the following code is compiled and run, it writes [David, Emma, Layla, Victoria] to the standard output.

By adding Victoria and removing Mike from the customer's list, it's clear that the class TestCustomer is able to modify the list.

How can we improve the encapsulation of the class Customer to achieve the following goals?

1. Other classes should be allowed to display the customer's list.
2. Other classes shouldn't be allowed to remove or add customers to the list.

import java.util.ArrayList;
 

public class TestCustomer
{
  public static void main(String[] args)
  {
    Customer customer = new Customer();
    customer.getCustomers().add("Victoria");
    customer.getCustomers().remove(2);
    System.out.print(customer.getCustomers());
  }
}


class Customer
{
  private ArrayList<String> customers;
  {
    customers = new ArrayList<>();
    customers.add("David");
    customers.add("Emma");
    customers.add("Mike");
    customers.add("Layla");
  }
  public ArrayList<String> getCustomers()
  {
    return customers;
  }
}

The correct answer and its explanation will be included in the next quiz in two weeks! For more Java quizzes, puzzles, and assignments, take a look at my site!