Easy way to convert Iterable to Collection

java collections
Ula Krukar picture Ula Krukar · Jun 20, 2011 · Viewed 341.5k times · Source

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 creating a bunch of foreach loops in my code for such a simple thing.

Answer

ColinD picture ColinD · Jun 20, 2011

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.

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