Enthuware

Given the following code:

interface Readable{ } non-sealed class Device implements Readable { }

sealed class DocType implements Readable permits Book, Journal { }

final non-sealed class Book extends DocType{ }

final class Journal extends DocType{ }

Which types will fail compilation?


Book
Non-sealed implies that a class may have subclasses, while final implies that a class cannot be subclassed. Both are contradictory. That is why, a class cannot be both - final and non-sealed, at the same time.


Why is this answer correct?

Because it does fail compilation for the same reason as is given. Since the question asks which types will fail compilation, option 4, i.e. Book is a correct option.