Guice配置错误

Question

I'm trying to use Google Guice with the @Inject and @Singleton properties as follows:

I have:

1. A Module with an empty configure() method.
2. An interface IFoo
3. A class Foo (implementing IFoo), annotated with @Singleton, with a parameter-less constructor annotated with @Inject. This is the single annotated constructor.

The classes, constructor and interface are public, and still I'm getting the following error:

No implementation for IFoo was bound.

Answer 1

You mean you get the error when doing this?

IFoo foo = injector.getInstance(IFoo.class);

Well then it is obvious. If the configure() is empty how should guice know with what class to satisfy the dependency for IFoo .

Just add this in the configure() method and it should work. Now guice knows with what class to satisfy the dependency.

bind(IFoo.class).to(Foo.class);

---

If you don't want to configure this in the module you can annotate the interface. eg

@ImplementedBy(Foo.class)
public interface IFoo {
  ...
}

The @Singleton annotations only tells guice to return the same instance for the class (the Singleton Pattern) everytime a request for the class is made via Injector.getInstance() instead of creating a new instance everytime. But note that this is only a Singleton per Injector rather then per Classloader.