Using 'interface' and 'abstract' for methods should produce error

samples/dartcombat/player.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /** A local player (API known to the main isolate when creating players). */
-interface Player default PlayerImpl {
+abstract class Player {
 
-  Player();
+  factory Player() = PlayerImpl;
 
   final Future<SendPort> portToPlayer;
 
   void setup(Window window, int player);
 
   void set enemy(SendPort portToEnemy);
 
   void set _portForTest(SendPort testPort);
 }
 
 /** A remote enemy (API visible to a player to communicate with the enemy). */
-interface Enemy default EnemyImpl {
-  Enemy(SendPort port);
+abstract class Enemy {
+  factory Enemy(SendPort port) = EnemyImpl;
 
   /** tell the enemy that we are ready, receive confirmation asynchronously. */
   Future<int> ready();
 
   /** shoot asynchronously. */
   Future<int> shoot(int x, int y);
 }
 
 
 /**
@@ skipping 66 matching lines @@
 
   /** message indicating that the enemy is ready to play. */
   static const ENEMY_IS_READY = 3;
 
   /** message describing a shoot action. */
   static const SHOOT = 4;
 
   /** message to set up a test port, used to make tests non-flaky. */
   static const SET_PORT_FOR_TEST = 5;
 }