Solved Death Drop modification - ConcurrentModificationException Error

So I have this code to go through the players inventory on death and check their items. If the player has soup, nothing happens, but if the player has anything else, then it will remove that item from the death drop. But I'm getting the ConcurrentModificationException error.


Here's the code:

Code:java

 for(ItemStack i : e.getDrops())
{
ItemStack soup = new ItemStack(Material.MUSHROOM_SOUP);
 
if(!i.equals(soup))
{
e.getDrops().remove(i);
}
 
else return;
}

Any ideas?

 

EgyptianKing Either:

• Don't modify the List you are looping over (i.e calling e.getDrops().remove(i) when looping over e.getDrops())
• Use an Iterator

 

Without Iterator:

Code:java

 
List<ItemStack> toRemove = new ArrayList<ItemStack>();
for (ItemStack item : e.getDrops()) {
    if (!item.getType().equals(Material.MUSHROOM_SOUP) {
        toRemove.add(item);
    }
}
for (ItemStack remove : toRemove) {
    e.getDrops().remove(remove);
}
 

With Iterator:

Code:java

 
Iterator<ItemStack> drops = e.getDrops().iterator();
while(drops.hasNext()) {
    ItemStack current = drops.next();
    if(!current.getType().equals(Material.MUSHROOM_SOUP)) {
        drops.remove();
    }
}
 

 

It should be obvious which one of those two to use.

Anyway, here's my contribution...without iterator. Only works on indexed collections:

Code:java

List<ItemStack> drops = e.getDrops();
for (int i = 0; i < drops.size(); i++) {
    if (drops.get(i).getType() == Material.MUSHROOM_SOUP) {
        drops.remove(i--);
    }
}

 

That's going to throw an ArrayOutOfBoundsException. Don't post useless solutions.

Anywhosal, OP, use an Iterator. Not hard to use. Any example above may help.

 

sparta417 Where exactly will it do that. Please elaborate.

 

If the first ItemStack is MushroomSoup, it will try to access an element in the List with the index -1.

Not hard to comprehend.

I'll break it down for you and the OP of the supplied method:

List contains X amount of ItemStack objects/instances.

Loop through List.

First iteration:

ItemStack object/instance at index I (in this case, 0; 1st in the List) has Material.MUSHROOM_SOUP, remove object/instance at index I subtract 1. Result index is -1. Hence, ArrayOutOfBoundsException.

 

sparta417 Will it now. Please study the usage of postfix decrement.

 

i--;

is

i = i - 1;

Please learn Java properly before posting on your profile whining about new users on this forum.

It saddens me that you still don't understand.

 

sparta417 Fair warning: You probably should've quit while you were ahead. fireblast709 does know Java and I suspect he's not called fireblast for nothing. Ima take cover.

 

I'm not afraid to prove someone wrong when they just ask rhetorical questions whilst ironically attacking newbies at Java in this forum.

 

sparta417 you are as wrong as you can be . You seem to mix up prefix and postfix. In the case of prefix decrementing you would be completely right.

prefix decrementing: First decrement, then use i

Code:

int i = 0;
System.out.println(--i);

Will print -1, and i will be -1 afterwards.

postfix decrementing: First do something with i, then decrement

Code:

int i = 0;
System.out.println(i--)

Will print 0, and i will be -1 afterwards.

Let's commence with a walkthrough with a List of size 1:

• Beforehand, i = 0. Not so surprising since we just set it to 0.
• Next up, we check the guard like any standard for loop would do. The size is 1, and 0 < 1, thus we get in the loop
• At the moment that we call get(i--), it will use i = 0 like explained above. Hence, get(0) would return the first element, and i will be -1 after the removal has returned
• Loop has ended, we increment i by one as stated by the step. i is now 0
• Once more, we check the guard. It seems that the size is 0 due to our last removal, and i is 0. Since 0 < 0 is false, we break out of the for loop and continue with the rest of the code.

[Addition] Adding a snippet with output

Code:

List<String> list = new ArrayList<String>();
list.add("a");
list.add("b");
list.add("b");
list.add("a");
list.add("a");
for(int i = 0; i < list.size(); i++)
{
    System.out.println(i+": "+list.get(i));
    if(list.get(i).equalsIgnoreCase("b"))
        list.remove(i--);
}
System.out.println(list.size());

With the output:

Code:

0: a
1: b
1: b
1: a
2: a
3

 

sparta417 Please...There is a very significant difference between i-- and --i. Look it up. fireblast709 wasn't wrong. But I'm afraid you are.

 

sparta417 Get #rekt son!!!

 

Wth, guys. I step away for 2 hours and you go to war with each other :S

 

BillyGalbreath Ah the real problem is when people have a slight misconception about how something works, yet strongly believe they're in the right.

 

One minimal flaw of learning a programming language years back doesn't mean I get wrecked. Grow up, child.

 

Why must you throw these kinds of comments into your posts? What are you trying to prove, and to who?

 

Lol, silly hick. Stop asking rhetorical questions and go feed the cows.

 

I'm the child, yet you just used an insult based on his background, I think sir, you are the one that in fact needs to grow up!