Question of K&B book on Generic Collections

[L Yan]

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]

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

[L Yan]

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]

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]

Where can I find the errata for this book??

[Deepak Bala]

There is a link at the beginning of the SCJP forum page that points to the errata. Its grouped along with other important links