From the course: Java SE 11 Developer (1Z0-819) Cert Prep

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Possible and impossible casts

Possible and impossible casts - Java Tutorial

From the course: Java SE 11 Developer (1Z0-819) Cert Prep

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Possible and impossible casts

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- Let's investigate how the compiler addresses the question of whether a cast is actually possible or not before it allows you to write the code for it. First, we'll review the reference casting rules. A cast down a class hierarchy, and I'm being specific about class here, succeeds at compilation time. If the object isn't actually of the cast type, then the cast will fail at runtime, and it will throw a ClassCastException. Casts up the class hierarchy, again, specific to class hierarchy, are always valid and therefore redundant. The compiler permits them, though it's important to realize that your development environment, your IDE, might actually complain. That's not the same thing as the language not permitting it though. A cast across a class hierarchy is rejected at compile time. The point there is that the two classes do not share an "is-a" relationship in any way, and so that's just downright impossible. But what happens with interfaces? Generally speaking, if an assignment from…

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