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.

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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().

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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.

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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());
}