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Eager Components

Sting supports both lazily created components and eagerly created components. An component annotated with the @Eager annotation is considered eager as are all of the transitive non-supplier dependencies of the component. Eager components are created when the injector is constructed. Lazy components on the other hand are only created when the injector attempts to access the component.

A lazy component is useful when it is only accessed via a supplier dependency or if the component is accessed as a result of invoking an output method on an injector. Lazy components require additional book-keeping to ensure that they are not accessed before they are constructed. As a result they can increase the code-size unnecessarily if used inappropriately. See the performance document for further details.

The easiest way to understand it is look at example where we have a single component annotated with the @Eager annotation. The code for this component looks like:

@Injectable
@Eager
public class MyComponent3
{
  private final MyComponent1 _myComponent1;
  private final Supplier<MyComponent2> _myComponent2Supplier;

  MyComponent3( MyComponent1 myComponent1,
                Supplier<MyComponent2> myComponent2Supplier )
  {
    _myComponent1 = myComponent1;
    _myComponent2Supplier = myComponent2Supplier;
    ...
  }

  ...
  public void performAction()
  {
    _myComponent2Supplier.get().calculate();
  }

  ...
}

We would expect that the component MyComponent1 and MyComponent3 would be constructed when the injector is constructed as MyComponent3 is explicitly annotated with the @Eager annotation and MyComponent1 is a dependency of MyComponent3. MyComponent2 is not constructed until the first time that the MyComponent3.performAction() method is invoked as it invokes the get() method on the supplier.