How to check if an Object is a Collection Type in Java?

Question

By using java reflection, we can easily know if an object is an array. What's the easiest way to tell if an object is a collection(Set,List,Map,Vector...)?

Answer 1

if (x instanceof Collection<?>){ }  if (x instanceof Map<?,?>){ } 

Answer 2

Update: there are two possible scenarios here:

1. You are determining if an object is a collection;

2. You are determining if a class is a collection.

The solutions are slightly different but the principles are the same. You also need to define what exactly constitutes a "collection". Implementing either Collection or Map will cover the Java Collections.

Solution 1:

public static boolean isCollection(Object ob) {   return ob instanceof Collection || ob instanceof Map; } 

Solution 2:

public static boolean isClassCollection(Class c) {   return Collection.class.isAssignableFrom(c) || Map.class.isAssignableFrom(c); } 

(1) can also be implemented in terms of (2):

public static boolean isCollection(Object ob) {   return ob != null && isClassCollection(ob.getClass()); } 

I don't think the efficiency of either method will be greatly different from the other.