Question

public void drop（String name） - 如果合适，从ArrayList中删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）玩家没有持有该物品，2）房间已经有物品，或3）玩家已成功将物品丢弃在房间内。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：我正在讨论的问题是，当我运行此方法并尝试在一个房间中删除一个项目时，它不会跳到else语句并重新发出消息“你没有那个项目”，我不知道为什么它这样做并没有通过第一个if语句，因为我输入的项目名称我知道是在arraylist中。

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

这将抛出ConcurrentModificationException因为您在修改列表时无法使用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阵列。像这样更改你的for循环以消除错误。你也正在使用if循环。不要要求完整的条件是假的，而只要在你之前写一个!就是假的。

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，你的代码还有一个逻辑缺陷，它在每次迭代后设置消息，而你可能希望它在设置currentMessage之前查看整个列表。

搜索arraylist，从arraylist中删除项目，将其添加到其他地方

3 个答案: