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

Using a debugger, I determined that Array.asList(titles) returns an "Arrays$ArrayList" (ie an inner class of the Arrays class) rather than a java.util.ArrayList.

It's always best to use the interface on the left side of expressions, in this case List rather than the concrete ArrayList. This works fine:

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