Consider an existing chain of objects, something like...
Group
contains List<Person>
Person
contains Head[, Body, Arms, Legs]
Head
contains Eyes[, Ears, Nose, Hair]
Let's say you have want to add an attribute to eyes and want that
attribute to be shared among each person in the group (maybe they're a
family and have shared genes). If you want to the eyes of each person
in the group to know the GenePool, then doing this by hand would
require that you
a) Construct the Group with a GenePool so that you can
construct a Person with a GenePool so that you can
construct a Head with a GenePool so that you can
construct the Eyes with the correct GenePool.
or
b) Have some static accessor somewhere that Eyes calls out to (a
service lookup)
On the contrary, if you do this through non-hand-coded DI then the
objects are constructed for you with only the dependencies they
directly need to have.
That is the main difference between hand-coded DI & a DI library such
as Guice or Spring. When you hand-code DI, you necessarily need to
pass dependencies through each parent class, even if that parent class
doesn't need the dependency directly. Library-guided DI allows your
objects to only care about their direct dependencies.
Sam
On Thu, Sep 11, 2008 at 8:28 PM, Pyrolistical <[EMAIL PROTECTED]> wrote:
>
> I have watched that, and I don't see why DI by hand is any worst than
> Guice. Its solves all your main problems with testability.
>
> The ClientFactory in your DI by hand example is very similar to a
> Provider in a Module for the Injector.
>
> So how is Guice any better than DI by hand?
>
> On Sep 11, 5:17 pm, "Bob Lee" <[EMAIL PROTECTED]> wrote:
>> On Thu, Sep 11, 2008 at 5:10 PM, Pyrolistical <[EMAIL PROTECTED]> wrote:
>>
>> > This is my point. If using new breaks Guice, then what's the point of
>> > Guice.
>>
>> > If I need to pass an Injector around to create classes, why don't I
>> > just pass in the dependencies when I use the new constructor? I can
>> > just replace the Injector with a class that holds references to my
>> > dependencies. I would create this class at main just like configuring
>> > a module.
>>
>> > If I did that, what's the point of Guice?
>>
>> http://crazybob.org/2007/06/introduction-to-guice-video-redux.html
>>
>> Bob
> >
>
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