InjectOnlyDirectDependencies

Inject only direct dependencies

Avoid injecting an object only as a means to get at another object. For example, don't inject a Customer as a means to get at an Account:

public class ShowBudgets {
   private final Account account;

   @Inject
   ShowBudgets(Customer customer) {
     account = customer.getPurchasingAccount();
   }

Instead, inject the dependency directly. This makes testing easier; the test case doesn't need to concern itself with the customer. Use an @Provides method in your Module to create the binding for Account that uses the binding for Customer:

public class CustomersModule extends AbstractModule {
  @Override public void configure() {
    ...
  }

  @Provides
  Account providePurchasingAccount(Customer customer) {
    return customer.getPurchasingAccount();
  }

By injecting the dependency directly, our code is simpler.

public class ShowBudgets {
   private final Account account;

   @Inject
   ShowBudgets(Account account) {
     this.account = account;
   }