aspose file tools*
The moose likes Programmer Certification (SCJP/OCPJP) and the fly likes generics Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login


Win a copy of Java 8 in Action this week in the Java 8 forum!
JavaRanch » Java Forums » Certification » Programmer Certification (SCJP/OCPJP)
Bookmark "generics" Watch "generics" New topic
Author

generics

swaraj gupta
Ranch Hand

Joined: Oct 22, 2010
Posts: 181

This is from KS & BB book..


Please let me know the exact relationship in-between Comparable<DVDInfo> and compareTo(DVDInfo d). How should i read them?
As whenever i try to differ the Comparable's concrete type and compareTo() methods argument, it gives a compile time error.

This is what given in the book: "In line 1 we declare that class DVDInfo implements Comparable in such a way
that DVDInfo objects can be compared to other DVDInfo objects
". which is turning out to be an insufficient information for me..
Prasad Kharkar
Ranch Hand

Joined: Mar 07, 2010
Posts: 438

@swaraj
what you are trying to implement using different types is unknown to us
so please post it here

and
about line 1
that surely says that, we can compare objects of type DVDInfo

what you have written is correct , DVDInfo objects getting compared means that
we can determine whether two DVDInfo objects are equal or less than or greater than with each other on the basis of its instance variable
for example



here,
compareTo() method is called whenever we sort the array of the DVDInfo objects and that sorting order is determined using the price

hope this is clear to you now

and post your code please
hth

SCJP 6 [86%] June 30th, 2010
OCPWCD [84%] March 26th, 2013
If you find any post useful, click the "plus one" sign on the right
swaraj gupta
Ranch Hand

Joined: Oct 22, 2010
Posts: 181

This is what I was trying to do...as i didn't get the point...
case 1:

case 2:
Please let me know the problem with these cases.
Matthew Brown
Bartender

Joined: Apr 06, 2010
Posts: 4244
    
    7

Well, the interface definition is:
So, if you implement Comparable<DVDInfo>, the interface definition tells you that there should be a method compareTo(DVDInfo). Anything else and you'll get a compiler error (unless it's an abstract class) because you simply haven't implemented the interface. As far as the compiler is concerned, it's exactly the same situation as if you'd omitted the compareTo method entirely.
 
It is sorta covered in the JavaRanch Style Guide.
 
subject: generics
 
Similar Threads
Comparable interface problem
Sorting objects using comparator doesnt work
Comparable interface problem.
compareTo
Collection and tostring() method overridden