s might be quite different from one another, we can create an array of references to them — as long as we treat them as superclass objects. But the reverse isnot true: A superclass object cannot always be treated a subclass object. For example, a Shape isnot always a Circle. Despite the fact that a subclass object also “ isa” superclass object, the subclass type and the superclass type are different. Subclass objects can be treated as superclass objects. This makes sense because the subclass has members corresponding to each of the superclass members — remember that the subclass normally has more members than the superclass has. Assignment in the other direction isnot allowed because assigning a superclass object toa subclass reference would leave the additional subclass members undefined.
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