Easy way to change Iterable into Collection
In my application I use 3rd party library (Spring Data for MongoDb to be exact).
Methods of this library return Iterable<T> , while the rest of my code expects Collection<T> .
Is there any utility method somewhere that will let me quickly convert one to the other. I would like to avoid making a banch of foreach loops in my code for such a simple thing.
With Guava you can use Lists.newArrayList(Iterable) or Sets.newHashSet(Iterable), among other similar methods. This will of course copy all the elements in to memory. If that isn't acceptable, I think your code that works with these ought to take Iterable rather than Collection . Guava also happens to provide convenient methods for doing things you can do on a Collection using an Iterable (such as Iterables.isEmpty(Iterable) or Iterables.contains(Iterable, Object) ), but the performance implications are more obvious.
In JDK 8, without depending on additional libs:
Iterator<T> source = ...;
List<T> target = new ArrayList<>();
source.forEachRemaining(target::add);
Edit: The above one is for Iterator . If you are dealing with Iterable ,
iterable.forEach(target::add);
您也可以为此编写自己的实用程序方法：
public static <E> Collection<E> makeCollection(Iterable<E> iter) {
Collection<E> list = new ArrayList<E>();
for (E item : iter) {
list.add(item);
}
return list;
}