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Question of K&B book on Generic Collections

L Yan
Greenhorn

Joined: Apr 25, 2006
Posts: 18
Hello,

Would somebody explain why option C is not correct? Thanks a lot.

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.)

C. ArrayList<Integer> input = null;
List<Number> output = null;
Deepak Bala
Bartender

Joined: Feb 24, 2006
Posts: 6662
    
    5

Please have a look at the errata for this book. This question is listed there.


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L Yan
Greenhorn

Joined: Apr 25, 2006
Posts: 18
Yes. I saw it on error list. But it doesn't have the correction.

Also I compiled the code, it did fail me because:

Group.java:14: incompatible types
found : java.util.List<capture of ? super java.lang.Integer>
required: java.util.List<java.lang.Number>
output = process(input);
^
1 error

I don't know why java.lang.Number is not ? super java.lang.Integer.

Thanks.
Deepak Bala
Bartender

Joined: Feb 24, 2006
Posts: 6662
    
    5

According to my copy of the book the answers are b e f after you change List<? super E> to List<E>. I have not looked into the errata but i think i remember someone acknowledging that change.
elPete Martin
Greenhorn

Joined: Apr 27, 2006
Posts: 5
Where can I find the errata for this book??
Deepak Bala
Bartender

Joined: Feb 24, 2006
Posts: 6662
    
    5

There is a link at the beginning of the SCJP forum page that points to the errata. Its grouped along with other important links
 
It is sorta covered in the JavaRanch Style Guide.
 
subject: Question of K&B book on Generic Collections