Re: IoC, DI, and a mess...

From:
andrewmcdonagh <andrewmcdonagh@gmail.com>
Newsgroups:
comp.lang.java.programmer
Date:
Wed, 6 Feb 2008 08:56:53 -0800 (PST)
Message-ID:
<6efdefe8-fbbd-4355-bb4f-b6dc238539ba@h11g2000prf.googlegroups.com>
On Feb 5, 5:33 pm, Daniel Pitts
<newsgroup.spamfil...@virtualinfinity.net> wrote:

Piotr Kobzda wrote:

Daniel Pitts wrote:

Now, the real trick is... The Computer has an InterruptTable,
PortTable, and InstructionTable instance, each of which have basically
a Map<Integer, Interrupt>, Map<Integer, Port>, etc... Is there a way
with Guice to set up that mapping? There is quite a bit of complex
wiring in that part of it too.


I think you can achieve this with a binding to a custom provider of each
map type (possibly additionally annotatedWith() in a case of mapping of
the same map types). Now you'll need a Module implementation for at
least a maps mappings, for example:

  binder.bind(new TypeLiteral<Map<Integer, Port>>() {})
    .toProvider(new Provider<Map<Integer,Port>>() {
      @Inject final Provider<Port> portProvider = null;

      public Map<Integer, Port> get() {
        Map<Integer, Port> map = new HashMap<Integer, Port>();
        // initialize a map... e.g.
        for(int i = 0; i < 10; ++i) {
          map.put(i, portProvider.get());
        }
        return map;
      }
    });
  // and similar for other maps...

piotr


Thanks, Unfortunately, each port/interrupt/instruction has a different
runtime type. eg. there are 47 concrete Instruction implementations,
something like 18 Interrupts, etc... So I currently have code that does:
instruction.put(1, new AddInstruction());
instruction.put(2, new SubtractInstruction());
...
instruction.put(47, new JumpInstruction());

I was thinking of externalizing the mapping to a file (properties or
xml), but I was holding off on that exercise until I needed different
arrangements of instructions.

I suppose I could externalize to a properties file, and then use the
binder you have shown, but that seems a bit messy to me.
--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>


I would suggest resisting externalising as long as possible. I've yet
to see any particular benefit of describing relationships in Property
files or XML, over just creating a Java class to do so. Indeed I see
a lot of people now wishing they had never externalised into XML and
some projects have even 'un-sprung' (think Spring framework)
applications.

Andrew

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