package auction.model;import java.io.Serializable;import java.util.Date;/** * This is the abstract superclass for BillingDetails. * <p> * A BillingDetails object is always associated with a single * User and depends on the lifecycle of that user. It represents * one of the billing strategies the User has choosen, usually * one BillingDetails is the default in a collection of many. * * @author Christian Bauer */public abstract class BillingDetails implements Serializable, Comparable {	private Long id = null;    private int version = 0;    private String owner;	private User user;	private Date created = new Date();	/**	 * No-arg constructor for JavaBean tools	 */	public BillingDetails() {}    /**     * Full constructor     */    protected BillingDetails(String owner, User user) {        this.owner = owner;        this.user = user;    }    // ********************** Accessor Methods ********************** //    public Long getId() { return id; }    public int getVersion() { return version; }    public String getOwner() { return owner; }    public void setOwner(String owner) { this.owner = owner; }    public User getUser() { return user; }	public Date getCreated() { return created; }	// ********************** Common Methods ********************** //    // TODO: This is not a very good equals() implementation    public boolean equals(Object o) {		if (this == o) return true;		if (!(o instanceof BillingDetails)) return false;		final BillingDetails billingDetails = (BillingDetails) o;        if (! (created.getTime() == billingDetails.created.getTime()) ) return false;		if (!getOwner().equals(billingDetails.getOwner())) return false;		return true;	}	public int hashCode() {		int result;		result = getCreated().hashCode();		result = 29 * result + getOwner().hashCode();		return result;	}	public int compareTo(Object o) {		if (o instanceof BillingDetails)            // Don't compare Date objects! Use the time in milliseconds!            return Long.valueOf(this.getCreated().getTime()).compareTo(                    Long.valueOf( ((BillingDetails)o).getCreated().getTime())                   );		return 0;	}	// ********************** Business Methods ********************** //	/**	 * Checks if the billing information is correct.	 * <p>	 * Check algorithm is implemented in subclasses.	 *	 * @return boolean	 */	public abstract boolean isValid();}