在arraylist中搜索，从arraylist中删除项，将其添加到其他位置

Question

public void drop（字符串名称）--如果合适，从ArrayList中移除该项，并将其添加到当前房间。使用以下选项之一更新游戏的消息：1）玩家没有持有该项目，2)房间已经有一个项目，或者3）玩家已经成功地将该项目放入房间。这是此方法的目标，但当我运行它时，它总是跳到else语句中的currentMessage。

问题：我遇到的问题是，当我运行这个方法并试图将一个项目放到房间中时，它没有，跳到else语句并重新发出消息“you do not have that Item”，我不知道为什么它会这样做，而不是通过第一个if语句工作，因为我键入的是一个我知道在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

您的问题是在迭代数组时不允许编辑它。像这样更改for循环以消除错误。另外，您正在使用if循环wronly。不要要求完整的条件为false，而只要求您希望在它之前编写！的条件为false。

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";
        }
    }
}