Hi Sang,
In studying the Example 3 (Polymorphic behavior via Java Interface) in the
Polymorphism lab of Javase, there is an interface class defined as follows:
public interface BookInterface extends ProductInterface {
public String getPublisher();
public void setPublisher(String publisher);
public int getYearPublished();
public void setYearPublished(int yearPublished);
}
Why does this class need to extend ProductInterface? I ask because Product
class already implements ProductInterface. So when you define the Book
class as:
public class Book extends Product* implements BookInterface*{ ...}
...it seems as though the Book class inherits ProductInterface twice: once
from extending Product and again in the BookInterface implementation.
*I modified the BookInterface definition by removing extends
ProductInterface and the code runs fine without error.
*So my questions are:
Is there a reason you extend BookInterface with ProductInterface? Or is
this simply superfluous coding?
And why does the compiler not complain in Book class that it inherits
ProductInterface interface twice: once from Product and again from
BookInterface? Is it Ok to inherit the same abstract methods twice like
this?
Joel
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