How to exclude exisiting objects when combining ArrayLists?

Question

Hi there, I'm new to Java and im trying to find a way to combine 2 ArrayLists and exclude any objects that may already exist in the customer ArrayList. I have a program that loads/saves data from a text file into a class object and I want the function to load the data 1 time and check if it already exisits.
I have tried using if(!customers.contains(obj)), but I think this only references the ArrayList Key and not the actual data.
Below is a test class I have been using to debug. Any help would be great!!!
public class test {
     public static void main(String[] args){
          ArrayList<Customer> temp  = new ArrayList<Customer>();
          ArrayList<Customer> customers  = new ArrayList<Customer>();
          Customer cs1 = new Customer(1,"sophie",'m',23,"asdasd");
          Customer cs2 = new Customer(1,"sophie",'m',23,"asdasd");
          Customer cs3 = new Customer(2,"asd",'m',23,"sdfghh");
          Customer cs4 = new Customer(3,"sdfff",'m',23,"hhhrrr");
          temp.add(cs1); temp.add(cs3); temp.add(cs4);
          customers.add(cs2);
          for(Customer c : temp){
               if(!customers.contains(c))
               customers.add(c);
          Collections.sort(customers, new CustomerComparator());
          System.out.println(customers);
          System.out.println(customers.contains(cs2));
}Edited by: newToJavaPro on May 21, 2010 10:18 PM

Answer 1

paulcw wrote:
newToJavaPro wrote:
Thanks for your reply I tried using a HashSet, which works for removing objects from the same origin, but it doesn't seem to remove the same data when added to the ArrayList from different objects. For example, id like to use cs1 to remove an instance of cs2 as they contain the same data but are assigned using different objects.No, that doesn't make any sense. More likely, you didn't properly override .equals() and hashcode(), so the set can't compare them properly. It seems to happen when they come "from different objects" because you're creating different instances of Customer each time, so the default implementations of .equals() and .hashcode() identify them as non-equivalent.Thanks, I I didn't realize HashSet and Equals compared object instance by default. Overridden methods and works a treat.