• anonymous
Interfaces are confusing me. I have asked classmates and no one knows, can you answer this? Suppose C is a class that implements the interfaces I and J. Which of the following assignments require a cast? C c = . . .; I i = . . .; J j = . . .; a. c = i; b. j = c; c. i = j; Thank you so much!
Computer Science
  • Stacey Warren - Expert
Hey! We 've verified this expert answer for you, click below to unlock the details :)
At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga. Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus. Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
  • katieb
I got my questions answered at in under 10 minutes. Go to now for free help!
  • anonymous
In general, a cast can be done implicitly only when it is 'safe', otherwise it has to be specified explicitly. A good way to understand it is by an example. In this case let's use direct inheritance, but it's the same idea when implementing interfaces. Say you have two classes `Zebra` and `Elephant` that inherit from `Mammal`. Obviously you can do: ``` Zebra z = new Zebra(); Elephant e = new Elephant(); ``` But the thing is, because `Zebra` inherits from `Mammal` (since logically every zebra is necessarily a mammal..) then the following logically works `Mammal m_z = new Zebra()`. Likewise we can do `Mammal m_e = new Elephant()`. But notice that the opposite is not logically true. A mammal is not necessarily a zebra (or an elephant). The cast from Mammal to Zebra is not safe, because `Zebra z = m_e` results in trying to treat an Elephant object (treated as Mammal) as a Zebra object, but an elephant is not a zebra.. oops. However that doesn't mean that the cast is always bad. The assignment `Zebra z = m_z` tries to treat an actual Zebra object (treated as Mammal) as a Zebra object. The thing is, as seen above, that the cast is not "safe", but not necessarily wrong. So if we want to perform such a cast we have to do so explicitly `Zebra z = (Zebra)m_z`. If you'd try this with an elephant: `Zebra z = (Zebra)m_e` the program would compile, but it performs bad cast which usually results in a runtime error trying to do so (depends on the language).

Looking for something else?

Not the answer you are looking for? Search for more explanations.