After miserably failing to answer question 50 from Marcus Green's mock exam #2 I figure I'd make my first post and see if anyone knows of any good examples or exercises to help illustrate Marcus's definition. (Found here: http://www.jchq.net/tutorial/05_01Tut.htm ) Question 50: Given the folowing classes which of the following will compile without error?
Any help would be much appreciated. Thanks in advance ...
posted 13 years ago
The rules are pretty simple: You can't instantiate an interface or abstract class. You can store an instantiated object in a type that is: a) itself b) its parent c) any interface implemented by itself d) any interface implemented by its parent Knowing that let's look at Marcus's example:
1 is an example of b - Object is the parent of CFace 2 is an example of b - Base is the parent of ObRef 3 is an error because you are storing an object in a variable that is its child type 4 is an example of b - Object is the parent of Base Remember, Object is the parent of everything in Java.