String[] str = (String[]) new Object[] { "Bla!"};.That gives a
ClassCastException. The short version of an explanation: an array instantiated by new Object[] is of a different class than one by new String[]. For the full glory of that fact, please see the Java Language Specification. As a teaser, I'll quote this snippet and its output from it:class Test {
public static void main(String[] args) {
int[] ia = new int[3];
System.out.println(ia.getClass());
System.out.println(ia.getClass().getSuperclass());
}
}
which prints:
class [Iclass java.lang.Object.
Of course, this can not work with static typing.
ReplyDeleteWhat's funny is even if String[] and Object[] are two different types, the JLS permits to downcast String[] to Object[], even though it's unsafe. But the opposite is forbidden as you experienced.
With generic lists, both operations are forbidden.
See http://stackoverflow.com/questions/2442337/common-ancestor-to-java-array-and-list/2442414#2442414
But C# has better support of co- and contra-variance, so you can do something conceptually like:
Iterator[Object] iter = new ArrayList[String]();
which is unsafe only if you add an Object. If the downcast is read-only like in the case of an iterator it's safe.