Guice bindings are keyed by a pair of (optional Annotation, Type).
In most circumstances, one doesn’t need the annotation, as there’s really just one active implementation:
bind(CoffeeMaker.class).to(RealCoffeeMaker.class);
...
@Inject Office(CoffeeMaker coffeeMaker) {}
However, in other circumstances, you want to bind a simple value (an integer, String, double, etc.). You should use a Qualifier annotation to allow you to get the right Integer back:
bindConstant().annotatedWith(HttpPort.class).to(80);
...
@Inject MyWebServer(@HttpPort Integer httpPort) {}
NOTE: Make sure that your annotation has the @Qualifier meta-annotation on
it, otherwise injection systems can’t see them. Guice users can optionally use
@BindingAnnotation, but Guice also understands @Qualifier.
This works great, but if your integer binding doesn’t include a Qualifier, it just means that you can ask Guice for “the Integer”, and it will give you a value back:
bind(Integer.class).toInstance(80);
...
@Inject MyWebServer(Integer httpsPort) {}
To avoid confusion in these circumstances, please use a Qualifier annotation when binding simple value types.
Suppress false positives by adding the suppression annotation @SuppressWarnings("BindingToUnqualifiedCommonType") to the enclosing element.