Initializing a Set with an Iterable

You can use Guava.

Set<T> set = Sets.newHashSet(iterable);

or to make it read like a sentence static import,

import static com.google.common.collect.Sets.*;

Set<T> set = newHashSet(iterable);

HashSet constructor relies on more than what Iterable offers: it wants to know the size of the collection up front in order to optimally construct the underlying HashMap. If you have a true, austere Iterable, which doesn't know its size, then you'll have to realize the Iterable up front by turning it into a regular Collection in any of a number of obvious ways.

If, on the other hand, you have a richer object that already knows its size, then it would pay to create a minimalist adapter class that wraps your Iterable into a collection, implementing just size in addition to forwarding the call to iterator.

public class IterableCollection<T> implements Collection<T>
{
   private final Iterable<T> iterable;

   public IterableCollection(Iterable<T> it) { this.iterable = it; }

   @Override public Iterator<T> iterator() { return iterable.iterator(); }

   @Override public int size() { return ... custom code to determine size ... }

   @Override .... all others ... { throw new UnsupportedOperationException(); }
}