无法将A类转换为B类

Question

What is the proper way to access the field level from instance of Minotaur ? Getting error in for (int i =0 ; i < ((Monster) this).level ; i++) which is Cannot cast from Player to Monster .

package player;

import monsters.*;

public class Player extends GameCharacter {

      public void performAttackOn(GameCharacter who){

    if (who instanceof Monster ){

        for (int i =0 ; i < ((Monster) this).level ; i++) { // << 

                 }

    public static  class Minotaur extends Monster{ // << nested class which is being created and there is need to access it's level

        public Minotaur () {

              type = "Minotaur";

        }
    }

}

---

package monsters;

public class Monster extends GameCharacter{

    public int level = 1;
}

---

package monsters;

public abstract class GameCharacter{

public static  class Minotaur extends Monster{

        public Minotaur(){
            type = "Minotaur";
             hitPoints = 30;
             weapon = new Weapon.Sword();

        }
    }
}

---

Minotaur should extend monsters.GameCharacter , monsters.Monster and override in Player.player some methods which was inherited from monsters.GameCharacter

Answer 1

Have the GameCharacter interface define a getLevel() method which Monster and Player both implement.

public interface GameCharacter
{
  public int getLevel( );
}

Once you've done that, you're taking advantage of polymorphism and don't even need to cast.

---

Also, do you really mean to cast this which is of type Player , to type Monster ? Or do you mean:

public void performAttackOn(GameCharacter who)
{
    for (int i =0 ; i < who.getLevel( ) ; i++)
    {
      // do stuff...
    }
}

Answer 2

In the hierarchy you have defined, a Player can never be a Monster so the cast is impossible.

I believe the line you are having issues with, based on the check above it, should reference who instead of this :

for(int i = 0; i < ((Monster)who).level; i++)

Answer 3

Thats pretty easy. You check if who is a Monter but if yes, you cast this to Moster and this refers to object in witch you currently are, it means some Player. replace this

((Monster) this).level

with this

((Monster) who).level

and the error should dissaper.

Answer 4

EDIT: Now I see, you can't have inheritance on fields of classes. You should have a common method

pubic int level();

in your GameCharacter . Then it's your choice if to define level as two different fields of children classes (not recommended) or just leave to GameCharacter to have a level field.

here: ((Monster) this).level you are casting the this instance, which is a Player to Monster . That's why you get the error.

Maybe you meant:

if (who instanceof Monster ){
  for (int i =0 ; i < ((Monster) who).level ; i++) { // << 

  }
}