Moritz Petersen

How do you convert a collection to a collection containing another type? Is that possible with standard Java? For example, you want to convert from Collection<String> to Collection<Integer>. Is that possible?

Now look at this piece of test code, this is how it should work:

    @Test
    public void testTransformedCollection() {
        List<String> strings = Arrays.asList("1", "2", "3");
        Collection<Integer> integers = new ConvertCollection<String, Integer>(strings) {
            @Override
            protected Integer convert(String s) {
                return Integer.valueOf(s);
            }
        };
        assertEquals(3, integers.size());
        Iterator<Integer> it = integers.iterator();
        int[] ints = {1, 2, 3};
        for (int i = 0; i < ints.length; i++) {
            assertTrue(ints[i] == it.next());
        }
    }

But does a ConvertCollection exist in any of the frameworks? How would it look like (assuming it would be immutable and only the most important methods are implemented?