通过arraylist搜索，从arraylist中删除项目，将其添加到其他地方

Question

public void drop (String name) - 如果合适，从 ArrayList 中删除该项目并将其添加到当前房间。使用以下选项之一更新游戏消息：1) 玩家没有持有该物品，2) 房间已有物品，或 3) 玩家已成功将物品放入房间。这是此方法的目标，但是当我运行它时，它总是跳到 else 语句中的 currentMessage。

问题： 我遇到的问题是，当我运行此方法并尝试将项目放入房间时，它不会跳到 else 语句并返回消息“您没有该项目”，我不知道为什么正在这样做并且没有通过第一个 if 语句，因为我正在输入一个我知道在 arraylist 中的项目名称。

public void drop(String name)
{      
    for(Item count : myArray){
        if(count.getName().contains(name) && currentRoom.hasItem() == false){
            currentRoom.addItem(count);
            currentMessage = "you have successfully dropped the item in the room";
            myArray.remove(count);
        }
        else if(count.getName().contains(name) && currentRoom.hasItem() == true)
        {
            currentMessage = "the room already has an item";
        }
        else 
        {
            currentMessage = "you do not have that item";
        }
    }
}

Answer 1

这将引发ConcurrentModificationException，因为在修改列表时不能使用foreach 循环。相反，迭代器支持 Iterator.remove() 方法，该方法允许您从基础集合中删除对象：

public void drop(String name)
{   
    Iterator<Item> it = myArray.iterator();
    Item count = it.next();
    while(count != null){
        if(count.getName().contains(name) && currentRoom.hasItem() == false){
            currentRoom.addItem(count);
            currentMessage = "you have successfully dropped the item in the room";
            it.remove();
        }
        else if(count.getName().contains(name) && currentRoom.hasItem() == true)
        {
            currentMessage = "the room already has an item";
        }
        else 
        {
            currentMessage = "you do not have that item";
        }
        count = it.next();
    }
}

Answer 2

您的问题是您在迭代时不允许编辑数组。像这样更改您的 for 循环以消除错误。您也错误地使用了 if 循环。不要要求完整的条件为假，而只要求您希望为假的条件，并在其前写上!。

public void drop(String name)
{      
    for (int i = 0; i < myArray.size(); i++) {
        Item count = myArray.get(i);
        if (count.getName().contains(name) && !currentRoom.hasItem()){
            currentRoom.addItem(count);
            currentMessage = "you have successfully dropped the item in the room";
            myArray.remove(count);
            i--; // element removed, so decrease count
        }
        else if(count.getName().contains(name) && currentRoom.hasItem() == true)
        {
            currentMessage = "the room already has an item";
        }
        else 
        {
            currentMessage = "you do not have that item";
        }
    }
}

Answer 3

试试这个；

public void drop(String name)
{
    for (Iterator<Item> it = col.iterator(); it.hasNext();)
    {
        Item count = it.next();
        if(count.getName().contains(name))
        {
            if(currentRoom.hasItem() == false)
            {
               currentRoom.addItem(count);
               currentMessage = "you have successfully dropped the item in the room";
               it.remove();
               return; //Once found return;
            }
            else
            {
               currentMessage = "the room already has an item";
               return; //Once found return or alternatively keep looking
            }
        }           
    }
    //Item never found
    currentMessage = "you do not have that item";       
}

除了 ConcurrentModificationException 之外，您的代码还有一个逻辑缺陷，它会在每次迭代后设置消息，而您可能希望它在设置 currentMessage 之前查看整个列表。