Why does Arrays.asList() return its own ArrayList implementation

Question

I recently found out that there are actually 2 different ArrayList implementations in Java (better late than never I guess...).

So I was wondering why d

Answer 1

They are two different classes with different behaviours.

The list returned when you called Arrays.asList is a thin wrapper over the array, not a copy. The list returned is fixed size: attempting to call add will throw an UnsupportedOperationException exception.

The java.util.ArrayList on the other hand keeps its own internal copy of the data and is variable sized.