SeletionKey.cancel（）和iterator.remove（）的区别-Java

Question

What is the difference of key.cancel() and iterator.remove()? Removing the key from iterator isn't removing the key from selector too?

Suppose that:

...
SelectionKey key = (SelectionKey) iterator.next();
..
Iterator<SelectionKey> iterator  = selectedKeys.iterator();
...

Answer 1

Javadoc for SelectionKey says following..

A selection key is created each time a channel is registered with a selector. A key remains valid until it is cancelled by invoking its cancel method, by closing its channel, or by closing its selector. Cancelling a key does not immediately remove it from its selector ; it is instead added to the selector's cancelled-key set for removal during the next selection operation.

iterator.remove, remove it from the list.

Answer 2

When you call remove() on an Iterator , it just removes the object the Iterator is currently on from the list. It doesn't call any methods on the object, it doesn't affect it in any way -- it just takes it out of the list.

When you call cancel() on a SelectionKey , it happens to do the same thing, but that's because cancel() requests that the list remove the object. In addition, it's not guaranteed to happen instantly, whereas using remove() immediately removes the item from the list. cancel() just makes it useless and, when it gets a chance, removes it from the list.