Get the class of java.util.Arrays$ArrayList

Question

How can I know the instance of java.util.Arrays$ArrayList. I\'ve tried this code snippet but it does not work at all :

if (myList instanceof Arrays)         


        

Answer 1

Why are you using Arrays ? You must use ArrayList like in this code

if (myList instanceof ArrayList) {
    //Do something here.
}

Answer 2

java.util.Arrays$ArrayList is a private inner class of Arrays, returned by the Arrays.asList method.

Since it's a private class there is no way to get access to the class in a way that it can be used with the instanceof operator. You can do this check using reflection however:

Class<?> clazz = Class.forName("java.util.Arrays$ArrayList");
// ...
clazz.isAssignableFrom(myList)

But I do not recommend doing that. It's a good practice to program against an interface. In this case the List interface defines the behavior of the object. The actual class of the object shouldn't matter.

Answer 3

in case the list comes from Arrays#asList, the returned ArrayList is NOT java.util.ArrayList, therefore a comparison to this class will always fail.

The question is, why do you need to know that it is exactly this implementation ? Maybe it is enough to check for java.util.List ?

In general it is questionable why you need the instanceof operator at all, often there are other design solutions better.