InjectingTheInjector

Use the Injector as little as possible (preferably only once)

Guice has a built-in binding for the Injector but it should be used sparsely.

Don't pass injectors into other injected objects through the constructor (which is also called "injecting the injector"). You should declare your dependencies statically.

Injecting the injector makes it impossible for Guice to know ahead-of-time that your Dependency Graph is complete, because it lets folks get instances directly from the injector. So long as nothing injects the injector, then Guice will 100% fail at Guice.createInjector time if any dependency isn't configured correctly. However, if something injects the injector, then Guice might fail at runtime (when the code lazily calls injector.getInstance) with missing bindings error.