`@Adaptive`注解标注在类上有什么特别之处？

```
ExtensionLoader(Class type, ExtensionDirector extensionDirector, ScopeModel scopeModel) {
this.type = type;
this.extensionDirector = extensionDirector;
this.extensionPostProcessors = extensionDirector.getExtensionPostProcessors();
initInstantiationStrategy();
this.injector = (type == ExtensionInjector.class ? null :
extensionDirector.getExtensionLoader(ExtensionInjector.class).getAdaptiveExtension()); // ①
this.activateComparator = new ActivateComparator(extensionDirector);
this.scopeModel = scopeModel;
}
```

为什么①处不直接使用`this.injector = (type == ExtensionInjector.class ? null :
extensionDirector.getExtensionLoader(ExtensionInjector.class).getExtension("adaptive"));`呢？不太明白`@Adaptive`注解标注在类上有什么特别之处？