ClassCastException using Iterables from Guava

I am trying to use the Iterables class to filter an ArrayList, but when I try to cast the result back to the original type I get a ClassCastException at runtime.

// domains is an ArrayList<Domain> which is defined earlier in the class
Iterable<Domain> temp = Iterables.filter(domains, new Predicate<Domain>() {
    public boolean apply(Domain input) {
        if (input.getName().toLowerCase().contains(filter.toString().toLowerCase())) {
            return true ;
        } else {
            return false;
        }
    }
}) ;
ArrayList<Domain> filteredDomains = (ArrayList<Domain>) temp ; // Error occurs here

To be complete, I am trying to use this in an开发者_C百科 Android application with a target of 1.6.

temp is not an ArrayList<Domain>. It is an Iterable<Domain>.

If you absolutely need an ArrayList<Domain> (or a List<Domain> in general), then you need to take a slightly different approach.

First, use Collections2.filter() instead of Iterables.filter(): to produce temp and then create a new ArrayList from the resulting Collection:

Collection<Domain> temp = Collections2.filter(domains, myPredicate) ;
List<Domain> filteredDomains = new ArrayList<Domain>(temp);

But you should really think if you need a List or ArrayList and if a Collection is not enough for what you want. If an Iterable is sufficient (for example if you only iterate over the content), then you can even keep using Iterables.filter().

The real return type is an anonymous class that extends IterableWithToString - and we cannot cast that type to ArrayList.

Here's the implementation on grepcode.

Temp is an Iterable not an ArrayList. Further more an ArrayList is an Iterable but not vice versa. What if you had

Iterable<?> iterable = new HashSet<?>();

You can see why a class cast exception would happen here.

To create an ArrayList from the Iterable you would have to iterate over the iterable itself and add to a new ArrayList

List<Domain> filteredDomains = new ArrayList<Domain>();

for(Iterator<Domain> i = temp.iterator(); i.hasNext();){
  filteredDomains.add(i.next());
}