wood burning stoves*
The moose likes Programmer Certification (SCJP/OCPJP) and the fly likes Enthuware Toughest questions on Collections Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login
JavaRanch » Java Forums » Certification » Programmer Certification (SCJP/OCPJP)
Bookmark "Enthuware Toughest questions on Collections" Watch "Enthuware Toughest questions on Collections" New topic
Author

Enthuware Toughest questions on Collections

Mohit G Gupta
Ranch Hand

Joined: May 18, 2010
Posts: 634


Toughest Questions for Oracle Java Programmer Certification
Enthunware


Q. No. 11







What will it print when it is compiled and run?



(a) It will compile with a warning and run without throwing an exception.
(b) It will compile without a warning and will throw an exception when run.
(c) It will compile and run without warning and exception.
(d) It will print 10 and -1.
(e) It will print 10 and 0.
(f) It will print 10.


answer are b,f

shouldn't be answer be 10 ,null
as get returns null if there is no value corresponding to given key


please help



OCPJP 6.0 93%
OCPJWCD 5.0 98%
Abimaran Kugathasan
Ranch Hand

Joined: Nov 04, 2009
Posts: 2066

Don't you execute this code? What is the answer?


|BSc in Electronic Eng| |SCJP 6.0 91%| |SCWCD 5 92%|
Mohit G Gupta
Ranch Hand

Joined: May 18, 2010
Posts: 634

i have removed
b.setIsbn("111");

from the code and then ran the program

.The output is same as given in the answer 10 followed by a Exception

help
Sumit Khurana
Ranch Hand

Joined: Sep 19, 2010
Posts: 68

HashMap add the key,value pair by using hashcode and equals method but book class does not implement the hash code and equals. so,every new object is different from the previous one and you can't search through the hashmap unless you have the reference of object when you are adding in the hashMap.


Exception occurs because when you execute the method
bs.getNumberOfCopies(b);

this method starts finding the b in HashMap and it does not find any b object because each object is different(because we have not implemented the hashcode). and hashmap returns null.

int getNumberOfCopies(Book b){

return map.get(b); //now here exception occurs because jvm can't convert null to zero..

}
Sumit Khurana
Ranch Hand

Joined: Sep 19, 2010
Posts: 68

Sumit Khurana wrote:
int getNumberOfCopies(Book b){

return map.get(b); //now here exception occurs because jvm can't unbox null to zero..

}
Arjun Srivastava
Ranch Hand

Joined: Jun 23, 2010
Posts: 432

hi sumit,see this question


SCJP 6 | FB : Java Certifications-Help. | India Against Corruption
Sumit Khurana
Ranch Hand

Joined: Sep 19, 2010
Posts: 68

in this question...what is the problem??
 
I agree. Here's the link: http://aspose.com/file-tools
 
subject: Enthuware Toughest questions on Collections