多态性中是否可以使用超类的对象访问子类的变量 [英] Is it possible to access variable of subclass using object of superclass in polymorphism
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问题描述
如何使用类KalaPlayer
的对象访问类KeyBoardPlayer
的状态变量?
How can I access state variable of class KeyBoardPlayer
with an object of class 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);
}
}
}
推荐答案
您不能.
无法从其父级访问子类的成员.如果有的话,以下内容将导致整体混乱:
There is no ability access members of a subclass from its parent. If there were, the following would cause mass chaos:
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
{
}
然后:
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();
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