On 1/6/2013 2:19 PM, Deepak A L wrote:
Hi Joel/Sang,
Can u plz provide the complete working example for
the below
Example 3--polymorphic behaviour.
OK. The new hands-on lab has been uploaded. I ended up modifying
interface code from
public interface BookInterface extends ProductInterface{
public String getPublisher();
public void setPublisher(String publisher);
public int getYearPublished();
public void setYearPublished(int yearPublished);
}
to
public interface BookInterface {
public String getPublisher();
public void setPublisher(String publisher);
public int getYearPublished();
public void setYearPublished(int yearPublished);
}
while the Book.java as it is as shown below
public class Book extends Product implements BookInterface{
private String publisher;
private int yearPublished;
/** Creates a new instance of Book */
public Book(double regularPrice,
String publisher,
int yearPublished) {
super(regularPrice);
this.publisher = publisher;
this.yearPublished = yearPublished;
}
...
This way, we are still showing Interrface-based (ProductInterface.java)
polymorphism while removing the redundancy Joel has pointed out
in his original question.
-Sang
-----
Deepak
On Jan 6, 2013 9:23 PM, "Sang Shin" <[email protected]
<mailto:[email protected]>> wrote:
On 1/5/2013 5:53 PM, Joel wrote:
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.
Your observation indeed is correct.
_I modified the BookInterface definition by removing extends
ProductInterfaceand 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?
The latter. :-) Apparently the only reason it also extends
Product class is
to use a constructor method of the Product class but it does not have
to as you pointed out. (The sample code actually uses this
I also found there is some discrenpancy between the document and
the code sample, which I am in the process of cleaning up.
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?
Correct. This is a not compiler error.
-Sang
Joel
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