是否应使用反射或实例化来确定类是否存在并实现接口？

Question

I want to determine if a class exists and whether or not it implements an interface. Both of the below should work. Which should be preferred and why?

//check if class exists, instantiate it and find out if it implements Annotation

  if(class_exists($classname)){
   $tmp=new $classname;
   if($obj instanceof Annotation) {//do something}
  }

//check if class exists, make a reflection of it and find out if it implements Annotation

  if(class_exists($classname)){
   $r=new  new ReflectionClass($classname);
   if($r->implementsInterface('Annotation)) {//do something}
  }

Answer 1

Check out these functions

• class_implements return the interfaces which are implemented by the given class
• class_parents return the parent classes of the given class
• is_a checks if the object is of this class or has this class as one of its parents

I'd prefer these over the Reflection class for introspection of a class or instance thereof. The Reflection API is for reverse-engineering classes.

There is also a number of other userful native function like interface_exists or property_exists, etc.