Contact.java

/**
 * A contact is a person we are making business with or may do in the future.
 *
 * Contacts have an ID (unique, a non-zero positive integer), 
 * a name (not necessarily unique), and notes that the user 
 * may want to save about them.
 */
public interface Contact {
    /**
     * Returns the ID of the contact.
     *
     * @return the ID of the contact.
     */
    int getId();

    /**
     * Returns the name of the contact.
     *
     * @return the name of the contact.
     */
    String getName();

    /**
     * Returns our notes about the contact, if any.
     *
     * If we have not written anything about the contact, the empty
     * string is returned.
     *
     * @return a string with notes about the contact, maybe empty.
     */
    String getNotes();

    /**
     * Add notes about the contact.
     *
     * @param note the notes to be added
     */
    void addNotes(String note);
}