extensions/assistedinject/src/com/google/inject/assistedinject/FactoryProvider2.java
@Inject
  @Toolable
  void initialize(Injector injector) {
    if (this.injector != null) {
      throw new ConfigurationException(
          ImmutableList.of(
              new Message(
                  FactoryProvider2.class,
                  "Factories.create() factories may only be used in one Injector!")));
    }

    this.injector = injector;

    for (Map.Entry<Method, AssistData> entry : assistDataByMethod.entrySet()) {
      Method method = entry.getKey();
      AssistData data = entry.getValue();
      Object[] args;
      if (!data.optimized) {
        args = new Object[method.getParameterTypes().length];
        Arrays.fill(args, "dummy object for validating Factories");
      } else {
        args = null; // won't be used -- instead will bind to data.providers.
      }
      getBindingFromNewInjector(
          method, args, data); // throws if the binding isn't properly configured
    }
  }
@Inject
  @Toolable
  void initialize(Injector injector) {
    if (this.injector != null) {
      throw new ConfigurationException(
          ImmutableList.of(
              new Message(
                  FactoryProvider2.class,
                  "Factories.create() factories may only be used in one Injector!")));
    }

    this.injector = injector;

    for (Map.Entry<Method, AssistData> entry : assistDataByMethod.entrySet()) {
      Method method = entry.getKey();
      AssistData data = entry.getValue();
      Object[] args;
      if (!data.optimized) {
        args = new Object[method.getParameterTypes().length];
        Arrays.fill(args, "dummy object for validating Factories");
      } else {
        args = null; // won't be used -- instead will bind to data.providers.
      }
      getBindingFromNewInjector(
          method, args, data); // throws if the binding isn't properly configured
    }
  }
At injector-creation time, we initialize the invocation handler. At this time we make sure all
factory methods will be able to build the target types.