Est-il possible d'accéder à la variable de la sous-classe en utilisant l'objet de la superclasse dans le polymorphisme

Question

Comment puis-je accéder à la variable d'état de la classe KeyBoardPlayer avec un objet de classe KalaPlayer?

/** 
    * An abstract class representing a player in Kala. Extend this class 
    * to make your own players (e.g. human players entering moves at the keyboard 
    * or computer players with programmed strategies for making moves). 
    */ 
public abstract class KalaPlayer { 

    /** 
     * Method by which a player selects a move. 
     * @param gs The current game state 
     * @return A side pit number in the range 1-6 
     * @throws NoMoveAvailableException if all side pits for the player are empty 
     * (i.e. the game is over) 
     */ 
    public abstract int chooseMove(KalaGameState gs) throws NoMoveAvailableException; 

} 



public class KeyBoardPlayer extends KalaPlayer { 
    /** 
    * Method by which a player selects a move. 
    * @param gs The current game state 
    * @return A side pit number in the range 1-6 
    * @throws NoMoveAvailableException if all side pits for the player are empty 
    * (i.e. the game is over) 
    */ 
    public KalaGameState state; 

    public KeyBoardPlayer() { 
     System.out.println("Enter the number of stones to play with: "); 
     try { 
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); 
      int key = Integer.parseInt(br.readLine()); 
      state=new KalaGameState(key); 
      //key=player1.state.turn; 
     } catch(IOException e) { 
      System.out.println(e); 
     } 
    } 

    public int chooseMove(KalaGameState gs) throws NoMoveAvailableException{ 
     return 0; 
    } 
} 

import java.io.IOException; 
import java.io.BufferedReader; 
import java.io.InputStreamReader; 

public class KalaGame { 
    KalaPlayer player1,player2; 

    public KalaGame(KeyBoardPlayer Player1,KeyBoardPlayer Player2) { 
     //super(0); 
     player1=new KeyBoardPlayer(); 
     player2 = new KeyBoardPlayer(); 
     //player1=Player1; 
     //player2=Player2; 
     //player1.state ****how can i access the stae variable from Keyboard CLass using object from KalaPlayer 
     key=player1.state.turn; 
    } 

    public void play() { 
     System.out.println("Enter the number of stones to play with: "); 
     try { 
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); 
      int key = Integer.parseInt(br.readLine()); 
      System.out.println(key); 
      KalaGameState state=new KalaGameState(key); 
      printGame(); 
     } catch(IOException e) { 
      System.out.println(e); 
     } 
    } 
} 

Answer 1

Vous ne pouvez pas.

Il n'y a aucun membre d'accès de capacité d'une sous-classe de son parent. S'il y avait, ce qui suit provoquerait le chaos de masse:

public class Vehicle 
{ 

} 

public class Car extends Vehicle 
{ 
    SteeringWheel _wheel = new SteeringWheel(); 

    public SteeringWheel getSteeringWheel { return _wheel; } 

    public SteeringWheel setSteeringWheel(SteeringWheel value) 
    { 
     _wheel = value; 
    } 
} 

public class Bicycle extends Vehicle 
{ 

} 

Puis:

Vehicle myVehicle = new Bicycle(); 

// This call couldn't possibly work since Bicylce has no steering wheel 
// and Vehicle isn't aware of what the type of the is/isn't. 
SteeringWheel myWheel = myVehicle.getSteeringWheel(); 

Answer 2

Il est impossible de le faire.

Mais vous pouvez prendre la ligne:

public KalaGameState state;

et le mettre dans la définition de la classe KalaPlayer. Ceci suppose que chaque sous-classe de KalaPlayer devrait avoir un état de lui-même.

Vous pouvez toujours définir l'état dans votre constructeur pour chaque instance que vous créez.

Il s'agit donc plus d'un problème de conception que d'un problème de langage car votre super-classe doit contenir toutes les informations communes à toutes les sous-classes.