java – Injector. getInstance(..) Returns a new instance of the singleton

My module:

bind( Translator.class ).to( TranslatorImpl.class ).in( Scopes.SINGLETON );

Now I hope to get the same instance every time

Injector injector = ...;
injector.getInstance( Translator.class );

But if I do

injector.getInstance( TranslatorImpl.class );

I get a new instance every time Is this a mistake or an expected behavior?

Solution

This is the expected behavior because translatorimpl Class is not bound to the singleton scope, only translator class.

If you want two getinstances (..) If both return the same instance, you can bind the implementation to the singleton scope:

bind(Translator.class).to(TranslatorImpl.class);
bind(TranslatorImpl.class).in(Scopes.SINGLETON);
assertEquals(injector.getInstance(Translator.class),injector.getInstance(TranslatorImpl.class));

For more information, see https://github.com/google/guice/wiki/Scopes#applying -scopes.