在接口的@Override实现中解析通配符类型

Question

我一直在阅读Java中的通配符，但我无法弄清楚在接口方法声明的实现中如何解决集合的通配符类型。您可以在技术上通过检查集合中的某个对象来发现该类型，但这不会允许您解决集合中的类型，并且如果该集合为空，则会失败。

public interface SomeInterface { 
    void addAThing(Object thing); 
    void addAListOfThings(Collection< ?> things); 
} 

public class SomeInterfaceImplementation implements SomeInterface { 
    @Override 
    public void addAThing(Object thing) { 
     if (thing instanceof Foo) { 
      /* thing has been discovered to be of type Foo 
      so now it can be assigned to an explicit Foo object */ 
      Foo fooThing = (Foo) thing; 
     } 
    } 

    @Override 
    public void addAListOfThings(Collection< ?> things) { 
     //this fails if things is empty 
     if (things.toArray()[0] instanceof Foo) { 
      /* things type has been discovered(maybe) to be of type Foo 
      but now we are unable cast without an unchecked cast exception */ 
      Collection<Foo> fooThings = (Collection<Foo>) things; 
     } 
    } 
} 

有没有一种合适的方法我不知道这样做？