Hi,
I wonder why the Collection.addAll() method only accepts other Collections but not Iterables. Why is that?
Any similar method to do that for Iterables?
views:
101answers:
5
+6
A:
Presumably because the Collection interface was introduced in Java 1.2 whereas Iterable appeared only in 1.5, and changing the interface would break all existing implementations.
Michael Borgwardt
2010-09-30 15:23:20
doh!!!... you're right, what was I thinking. .... deleting... and plus onening
OscarRyz
2010-09-30 16:07:34
+2
A:
Basically because an iterable may never en ( that is, getNext() return true forever )
Also, to keep congruency, you may think a Collection may add all the elements of another collection, but, an iterable is not necesarily a collection ( it may be anything, like the a ResultSet wrapper for instance )
OscarRyz
2010-09-30 15:23:56
Ah, your first point is a good one. I don't really understand what you mean by the second one and how it would affect the `addAll` method.
Albert
2010-09-30 15:32:06
As for the second, an iterable is an interface, pretty much, anything, could implement it, and you may end up in the first situation, with an possible infinite loop.
OscarRyz
2010-09-30 15:40:30
Not sure I agree. A Collection can be infinite in the same way as an Iterable, as you can construct a valid Collection as a wrapper around an Iterable.
GaryF
2010-09-30 15:43:15
Nevermind, I've checked the doc, http://download.oracle.com/javase/6/docs/api/java/util/Collection.html#size%28%29 it should return Integer.MAX_VALUE
OscarRyz
2010-09-30 15:54:18
A:
Because not all Iterable objects are java.util.Collection.
E.g. java.sql.SQLException is iterable.
public class SQLException extends java.lang.Exception
implements Iterable<Throwable> {
How would collections interpret it? It wouldn't return a collection of it's parameterized type (of the collection).
The Elite Gentleman
2010-09-30 15:24:45
+5
A:
When in doubt, always check Guava (or Commons):
- Guava: Iterables.addAll
- Commons Collections: CollectionUtils.addAll
Michael Brewer-Davis
2010-09-30 15:25:10
+1 for *When in doubt, always check Guava*. Most apache commons libs are great, but commons / collections is annoying because it doesn't support generics.
seanizer
2010-09-30 15:48:56