casting Arrays.asList causing exception: java.util.Arrays$ArrayList cannot be cast to java.util.ArrayList

Question

I\'m new to Java and am trying to understand why the first code snippet doesn\'t cause this exception but the second one does. Since a string array is passed into Arrays.as

Answer 1

The problem is you specified your List to contain ArrayLists - and by implication no other List implementations. Arrays.asList() returns its own implementation of a List based on the implementation of the array parameter, which may not be an ArrayList. That's your problem.

More broadly, you have a classic code style problem: You should be referring to abstract interfaces (ie List), not concrete implementations (ie ArrayList). Here's how your code should look:

List> stuff = new ArrayList>();
String[] titles = { "ticker", "grade", "score" };
stuff.add((List) Arrays.asList(titles));

I have tested this code, and it runs without error.