aspose file tools*
The moose likes Programmer Certification (SCJP/OCPJP) and the fly likes About Chapter 7: Generics and 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 "About Chapter 7: Generics and Collections" Watch "About Chapter 7: Generics and Collections" New topic
Author

About Chapter 7: Generics and Collections

Zhao zhenhua
Ranch Hand

Joined: Jul 17, 2006
Posts: 37

In self test number 16th. I find a problem,it seems that every answer is wrong!!,why?

16.Given a method declared as:

public static <E extends Number> List<? super E> process(List<E> nums)

A programmer wants to use this method like this:

// INSERT DECLARATIONS HERE
output = process(input);
Which pairs of declarations could be placed at // INSERT DECLARATIONS HERE to allow the code to compile? (Choose all that apply.)

A. ArrayList<Integer> input = null;

ArrayList<Integer> output = null;

B ArrayList<Integer> input = null;

List<Integer> output = null;

c ArrayList<Integer> input = null;

List<Number> output = null;

d List<Number> input = null;

ArrayList<Integer> output = null;

e List<Number> input = null;

List<Number> output = null;

f List<Integer> input = null;

List<Integer> output = null;

g None of the above.

I try out every answer,but it compile wrong! Who can tell me why and explain how this work?

The compiler say:"Type mismatch: cannot convert from List<capture-of ? super Integer> to List<Number>" WHY
What it means "capture-of ?".I used following codes in eclipse3.3.

[ June 03, 2007: Message edited by: Zhao zhenhua ]

Head first Servlet and JSP
Chandra Bhatt
Ranch Hand

Joined: Feb 28, 2007
Posts: 1707
See the K&B Errata. Link is available on the top of the SCJP forum.

The declared method is:


public static <E extends Number> List<E> process(List<E> nums)


Thanks,


cmbhatt
Zhao zhenhua
Ranch Hand

Joined: Jul 17, 2006
Posts: 37

If the method just is what you say,the answer is right ,Thank you Chandra
 
I agree. Here's the link: http://aspose.com/file-tools
 
subject: About Chapter 7: Generics and Collections