public class ActiveList {
        /** list of AuctionListing objects
         */
        private ArrayList<AuctionListing> auctListings;    

        // add methods and attributes from the class diagram
    };

    public class AuctionListing {

        // object references from aggregations and associations:
        private Item item;

        private BidHistory bidHist;

        private Seller seller;

        private Auctioneer auctioneer;

        // object attributes:
        private Date deadline;              // auction deadline

        private double startPrice;          // the auction starting price
    };

• for each object, an "incoming message" maps to a method that must be implemented by the object receiving the message.
• for a complete application implementation, all objects in all sequence diagrams must be considered according to these rules.
• the message name, return value and parameter list (signature) map to the method signature in the code implementation.
• the code implementation still must be fully defined even if the sequence diagram is high-level, or a message signature does not specify return value or parameters.
• the method implementation consists in part of the messages the object sends during the current message activation box. If object A sends a message m(...) to another object B, then the mapping to A's code is a call B.m(...).
• the message order from the sequence diagram must be preserved in the method code.
• sequence diagrams for alternate scenarios (e.g. success vs. failure scenario) may include the same message sent to a particular object, but showing a different sequence. The code from alternate sequences must be merged during the implementation using if-else branches. (see the listItem() method below)
  If the code gets too complicated, try breaking it into multiple (helper) methods.
• if object A sends a message to object B, then object A must have a reference to the B object (A calls B.someMethod()). The reference to B object may be an instance variable of the A object, or a local/temporary variable obtained indirectly (e.g. through accessors applied to third-party objects).
• consider adding such reference instance variables as appropriate.
• methods implementing messages between objects should have "package" or "public" visibility. Helper methods are "private".

    public class ActiveList {
        .......
        public void listItem(Item it, Date deadline, double price) {
            // create new AuctionListing (call constructor):
            AuctionListing al = new AuctionListing(it, deadline, price);

            // create auctioneer for this listing:
            Auctioneer au = new Auctioneer(al);

            // implementation choice: validateListing() returns true/false
            // if validation succeeds, add to ActiveList:
            if (au.validateListing()) {

                // add the new auction listing:
                this.auctListings.add(al);

                // schedule auction completion:
                au.scheduleCompletion();
            }
            else {
                // indicate error to user
                // ... omitted ...
            }
        }
        .......
    }