搜索arraylist，从arraylist中删除项目，将其添加到其他位置

Question

public void drop (String name) - if appropriate, remove the item from the ArrayList and add it to the current room. Update the game's message with one of the following options: 1) the player is not holding that item, 2) the room already has an item, or 3) the player has successfully dropped the item in the room. This is the goal of this method but when I run it it always skipps to the currentMessage in the else statement.

PROBLEM: The problem I am hacing is that when I run this method and try to drop an Item in a room, it doesnt and skips to the else statement and resturns the message "you do not have that item", and I do not know why it is doing this and not working through the first if statement because I am typing an items name I know is in the arraylist.

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

This is going to throw a ConcurrentModificationException because you cannot use a foreach loop while modifying the list. Instead iterators support the Iterator.remove() method that will allow you to remove an object from the underlying collection:

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

Your problem is that you are not allowed to edit the array while you are iterating through it. Change your for loop like this to get rid of the error. Also you are using the if loop wronly. Don't ask the complete condition to be false but only the one you want to be false with writing an ! before it.

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

Try this;

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";       
}

In addition to the ConcurrentModificationException your code also had a logical flaw in it, it set the message after every iteration, whereas you probably wanted it to look through the entire list before setting currentMessage.