Question

I'm using google-collections and trying to find the first element that satisfies Predicate if not, return me 'null'.

Unfortunately, Iterables.find and Iterators.find throws NoSuchElementException when no element is found.

Now, I am forced to do

Object found = null;
if ( Iterators.any( newIterator(...) , my_predicate )
{
    found = Iterators.find( newIterator(...), my_predicate )
}

I can surround by 'try/catch' and do the same thing but for my use-cases, I am going to encounter many cases where no-element is found.

Is there a simpler way of doing this?

Was it helpful?

Solution

It sounds like you should be using Iterators.filter, then checking the value of hasNext on the returned iterator.

OTHER TIPS

Since Guava 7, you can do this using the Iterables.find() overload that takes a default value:

Iterables.find(iterable, predicate, null);

This was filed as a feature request:

http://code.google.com/p/guava-libraries/issues/detail?id=217

We are actually in progress on it.

I'm not sure if this qualifies as simpler, but at least it avoids exceptions and requires only one pass over the source iterable:

public static <T> T findMatchOrNull(Iterator<T> source, Predicate<T> pred) {
    Iterator<T> matching = Iterators.filter(source, pred);
    Iterator<T> padded = Iterators.concat(matching, Iterators.<T>singletonIterator(null));
    return padded.next();
}
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