There is an example of Custom Injection in your class.
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface MyCustomInject {
Class whichClass();
}Usage
@MyCustomInject(whichClass = Dog.class)
public static Animal animal;
@MyCustomInject(whichClass = Horse.class)
public static Animal anotherAnimal;