在另一个类中使用特定于对象的变量

Question

我一直在查看所有其他问题，但似乎找不到问题的答案：我需要使用非静态字段（对于我创建的每个对象都是独立的）并且我需要访问该字段另一个类中的变量。一段代码：(Enemytank.java)

public class Enemytank extends MoveableGameItem implements IStepListener, IAlarmListener
{
    private Battlefield mygame;

    private Enemytank enemyTank1;   
    private static int enemyWaveSize = 1;
    private static int remainingKills = enemyWaveSize;
    private static double startupEnemyHealth = 100.00;
    private double enemyHealth = startupEnemyHealth;
    public int enemyStage = 0;              


    /**
     * Constructor.
     */
    public Enemytank(Battlefield mg)
    {
        mygame = mg;
        setImage("/images/enemytank.png", 27, 33);
        setPosition(25, 35);
        // snelheid 5, naar rechts
        setDirectionSpeed(0, 4);
        startMoving();
        mygame.addStepListener(this);
    }
}

我需要变量enemyStage的类：(Playertank.java)

public void collisionOccured(GameItem collidedItem)
    {
        Enemytank enemyTank1 = new Enemytank(mygame);
        System.out.println("pt= " + enemyTank1.getEnemyStage());
        if ((collidedItem instanceof Enemytank) && (playerShields > 0) && (enemyTank1.getEnemyStage() != 3))
        {
            this.playerShields--;
            mygame.setShieldsonDashboard(playerShields);

        }
        else if ((collidedItem instanceof Enemytank) && (playerShields <= 0) && (enemyTank1.getEnemyStage() != 3))
        {
            System.out.println("hit player!");
            this.playerLives--;
            mygame.setLivesonDashboard(playerLives);
        }
        if (collidedItem instanceof Shield)
        {
            this.playerShields++;
            mygame.setShieldsonDashboard(playerShields);
            mygame.deleteGameItem(collidedItem);
            this.playerUpgrades();
        }
    }

我现在从enemytank1.getEnemyStage() 得到的值是0，因为我相信我用EnemytankenemyTank1 = new Enemytank(mygame); 制作了一个新对象。。如何引用现有对象并获得该特定值？ enemyStage 用于检查怪物是死了还是快死了。

提前谢谢 :) 火焰

Answer 1

您需要利用多态性。在GameItem 类（或者它是接口？）中声明方法getEnemyStage，然后您将能够询问collidedItem.getEnemyStage() 并从该对象中获取数据。或者，向下转换将collidedItem 转换为EnemyTank 并调用方法：((EnemyTank)collidedItem).getEnemyStage()

另外，将enemyStage设为private，不必为public，因为它将通过调用getter方法间接访问。

if (collidedItem instanceof Enemytank && playerShields > 0 && 
    ((Enemytank)collidedItem).getEnemyStage() != 3) {
  ....
}

Answer 2

当您调用碰撞发生时，您将引用传递给对象。因此，将碰撞发生更改为：

public void collisionOccured(GameItem collidedItem, Enemytank enemyTank) //a change here
    {
        System.out.println("pt= " + enemyTank.getEnemyStage()); // now you can call enemyTank with the correct refrence
        if ((collidedItem instanceof Enemytank) && (playerShields > 0) && (enemyTank1.getEnemyStage() != 3))
        {
            this.playerShields--;
            mygame.setShieldsonDashboard(playerShields);

        }
        else if ((collidedItem instanceof Enemytank) && (playerShields <= 0) && (enemyTank.getEnemyStage() != 3))
        {
            System.out.println("hit player!");
            this.playerLives--;
            mygame.setLivesonDashboard(playerLives);
        }
        if (collidedItem instanceof Shield)
        {
            this.playerShields++;
            mygame.setShieldsonDashboard(playerShields);
            mygame.deleteGameItem(collidedItem);
            this.playerUpgrades();
        }
    }

而且，当您在 EnemyTank 类中调用 collisionOccured 时，您会喜欢这样：

collisionOccured(collidedItem, this); //where this refrence to this object (which is a EnemyTank)

有了这个答案，我假设您从 EnemyTank 类中调用了 collisonOccured，因为您没有发布该调用的位置。如果不是，则在调用 collisionOccured 时需要对 EnemyTank 的对象进行引用（因此将调用中的 this 更改为对正确对象的引用）