java - Serializing an object which contains a list of other objects -

background: implementing game needs serialize model objects (events) able send them on network clients playing game.

problem: 1 of model classes eventshowcards, subclasses event (declared serializable).

public class eventshowcards extends event {     private final player player;     private final list<itemcard> cards;      public eventshowcards(player player, list<itemcard> cards) {         super();         this.player = player;         this.cards = cards;     }      public player getplayer() {         return player;     }      public list<itemcard> getcards() {         return cards;     }      @override     public void accept(visitor visitor) {         visitor.visit(this);     } } 

however, when serialize object , send client, client receives object , list of itemcards empty. no exceptions thrown.

event shown server (before serialization):

event shown client (after serialization):

in order serialize/deserialize using standard objectoutputstream/objectinputstream

anyone has idea of happening here? thanks.

edit

as request posting code of itemcard (and card):

itemcard.java

public abstract class itemcard extends card {      /**      * default card ca played independently game state, subclasses have more complicated rules      * must override method.      */     public boolean canbeplayed(gamestateturn gamestate) {         return true;     }      protected void emiteventcardplayed(player cardplayer, gamestate gamestate)  {         notifyobservers(new eventcardplayed(cardplayer, this));     }  } 

card.java

public abstract class card extends concreteobservable<event> implements cardbehavior, serializable {     protected deck<? extends card> deck; // deck card belongs      public card() {         super();     }      public void setdeck(deck<? extends card> deck) {         this.deck = deck;     }      public void discard() {         deck.discard(this);     }      @override     public void preeffect(player cardplayer, gamestate gamestate) {         // default cards have no preeffects     }      @override     public void posteffect(player cardplayer, gamestate gamestate) {         // default after card played discarded         discard();     }      @override     public string tostring() {         string classname = this.getclass().getsimplename();         return cardnamefromclassname(classname);     }      private string cardnamefromclassname(string classname) {         stringbuilder sb = new stringbuilder();         (character c: classname.tochararray()) {             if (character.isuppercase(c)) {                 sb.append(" ").append(character.tolowercase(c));             } else {                 sb.append(c);             }         }         return "\"" + sb.substring(1) + "\"";     } } 

edit 2

and deck.java

public class deck<t extends card>         extends concreteobservable<event>         implements observer<event>, serializable {...} 

edit 3

the list of item cards used initialize eventshowcards created list model object of application, passed as-is. creating arraylist (copying object) somehow solved problem.

the list can contain unlimited number of object types.
have eventshowcards serialized (through event class), need force itemcardclass serializable in order marshalled , unmarshalled when needed correctly.

edit

java.util.list doesn't implement serializable, why list not serialized.
use other collections serializable arraylist