The easiest way to transform collection to array?

Question

Suppose we have a Collection<Foo>. What is the best (shortest in LoC in current context) way to transform it to Foo[]? Any well-known libraries are allowed.

UPD: (one more case in this section; leave comments if you think it's worth to create another thread for it): What about transforming Collection<Foo> to Bar[] where Bar has constructor with 1 parameter of type Foo i.e. public Bar(Foo foo){ ... } ?

Answer 1

Where x is the collection:

x.toArray (new Foo[x.size ()])

Answer 2

If you use it more than once or in a loop, you could define a constant

public static final Foo[] FOO = new Foo[]{};

and do the conversion it like

Foo[] foos = fooCollection.toArray(FOO);

The toArray method will take the empty array to determine the correct type of the target array and create a new array for you.

---

Here's my proposal for the update:

Collection<Foo> foos = new ArrayList<Foo>();
Collection<Bar> temp = new ArrayList<Bar>();
for (Foo foo:foos) 
    temp.add(new Bar(foo));
Bar[] bars = temp.toArray(new Bar[]{});

Answer 3

For the original see doublep answer:

Foo[] a = x.toArray(new Foo[x.size()]);

As for the update:

int i = 0;
Bar[] bars = new Bar[fooCollection.size()];
for( Foo foo : fooCollection ) { // where fooCollection is Collection<Foo>
    bars[i++] = new Bar(foo);
}    

Answer 4

Here's the final solution for the case in update section (with the help of Google Collections):

Collections2.transform (fooCollection, new Function<Foo, Bar>() {
    public Bar apply (Foo foo) {
        return new Bar (foo);
    }
}).toArray (new Bar[fooCollection.size()]);

But, the key approach here was mentioned in the doublep's answer (I forgot for toArray method).