调用他的方法后如何删除对象？

Question

I am doing a pc game. What I need is: after object Bomb make his attack I want to remove her from my ArrayList<Entity> .

Entity is my abstract class for all enemies, like bomb, archer... I use ArrayList to indicate what I need to draw and update. If it's possible, I want to remove that object at all, not just from ArrayList .

Here is my code of GameEngine class:

    public class GameEngine {
      gameEntities = new ArrayList<Entity>();
      Bomb bomb1;

      bomb1 = new Bomb();
      gameEntities.add(bomb1)
      public void update() {   
        for(Entity entity : gameEntities){
            entity.whatNow();
        }        
      }
    }

And other classes:

    public class Bomb extends Entity { 
      void whatNow() {
        GameData.entityRemove(this);
      }
    }

    public class GameData {
      static void entityRemove(Entity entity) {
        for(Entity listEntity : GameEngine.gameEntities){
            if(entity == listEntity){
                 listEntity = null;
                 GameEngine.gameEntities.remove(listEntity);
            }
      }
    }

Answer 1

An Entity in your context shouldn't directly access elements of the GameEngine . I would rather suggest something like this:

• your engine has two lists: one for current things, and one for future things
• your code simply walks trough the current list
• when processing an entry leads to a future event, one should call a method such as addFuture(Entity whatever) on the master GameEngine object
• when you are dong processing the current list - then you clear current and move all entries from future into it
• then you clear future and start processing current again

In other words: avoid removing entries. Simply process a list once, throw it away and collect "new" entries within a second list.

And unrelated: read about the @Override annotation and start using it.

Answer 2

You should let the bombs mark themself as "toClean" and let the GameEngine remove them after the whatNow() updates (I assume that your GameEngine is a singleton):

public class Bomb extends Entity { 
  void whatNow() {
    // do my bomb stuff
    GameEngine.instance().remove(this);
  }
}

public class GameEngine {

  // Declare a gameEntitiesToRemove queue/list

  public void update() {
    for(Entity entity : gameEntities){
       entity.whatNow();
    }
    while(gameEntitiesToRemove.hasNext()){
       gameEntities.remove(gameEntitiesToRemove.pop());
    }
  }

  public void remove(Entity entity) {
    this.gameEntitiesToRemove.add(entity);
  }
}

Answer 3

The problem is in the if-clause inside the for-loop:

listEntity = null;
GameEngine.gameEntities.remove(listEntity);

The second line would remove the listEntity from the ArrayList, if listEntity would not be set to null in the first line. Now it tries to remove null from the list, which is likely not what you want.

At the very least, swap these two lines. However there is really no point in setting listEntity to null, as a local variable it will be gone after that loop anyway.