Java - Iterate Hashmap?

Question

Iterator<Player> iterator = plugin.inreview.keySet().iterator();
while (iterator.hasNext()) {
    Player key = (Player) iterator.next();
    chat.getRecipients().remove(key);
}

This throws an: java.util.NoSuchElementException

at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
at java.util.HashMap$EntryIterator.next(Unknown Source)
at java.util.HashMap$EntryIterator.next(Unknown Source)

Any ideas as to why this is happening? When this occurs, there is one key (with one value) in the map.

What's the relationship between chat.getRecipients and plugin.inreview? — Jon Skeet
– Jon Skeet, Commented Oct 13, 2011 at 22:22
@JonSkeet There is no relation. This is for Minecraft. chat.getRecipients returns the list of players that will be messaged... this.plugin.inreview is a Hashmap with a key and a value. — Gray Adams
– Gray Adams, Commented Oct 13, 2011 at 22:30
if you comment out chat.getRecipients().remove(key);just for test and run it do you still get this error. I think there is a relationship and you are removing elements from same collection while iterating. — Shahzeb
– Shahzeb, Commented Oct 13, 2011 at 22:36

Zadish · Accepted Answer · 2022-08-24 05:59:31Z

2

Better solution for iterating a hashmap (java 8+):

Map<String, String> map = new HashMap<>();
map.put("key1", "value1");
map.put("key2", "value2");
// ...
// ...

map.forEach((key, value) -> {
    System.out.println("Key: " + key + ", Value: " + value);
})

answered Aug 24, 2022 at 5:59

Zadish

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Comments

Sanjay Manohar · Accepted Answer · 2011-10-13 22:27:41Z

1

My guess is that your getRecipients() returns the same collection as plugin.inreview!

This would mean that you try to remove an element from the collection while you are iterating over it. This is of course bad.

Instead, you should do this

Vector toRemove=new Vector();
Iterator<Player> iterator = plugin.inreview.keySet().iterator();
while (iterator.hasNext()) {
  Player key = (Player) iterator.next();
  toRemove.add(key);
}
chat.getRecipients().removeAll(toRemove);

Another possibility is that you have several threads?

answered Oct 13, 2011 at 22:27

Sanjay Manohar

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3 Comments

DwB Over a year ago

I agree, but prefer LinkedList to Vector. No good reason for my preference though.

Gray Adams Over a year ago

getRecipients() is different from plugin.inreview.

Gray Adams Over a year ago

The irony is that this identical bit of code is used in another .Java file and works perfectly fine. Both are setup the same way...

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