• Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other Pie Elite all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Paul Clapham
  • Tim Cooke
  • Jeanne Boyarsky
  • Liutauras Vilda
Sheriffs:
  • Frank Carver
  • Henry Wong
  • Ron McLeod
Saloon Keepers:
  • Tim Moores
  • Frits Walraven
  • Tim Holloway
  • Stephan van Hulst
  • Carey Brown
Bartenders:
  • Al Hobbs
  • Piet Souris
  • Himai Minh

Generics example, need help.

 
Greenhorn
Posts: 27
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Hi, I am posting this same question again because I still didn't get my doubt cleared. In this question, if B,E and F are correct then why is C not correct? Is it because both the input and output types should match in addition to the return type being an integer or a number?
I'm just thinking, if you feed in an ArrayList of integers according to answer C and get a List of numbers, it doesnt make sense since a number could be a Float too? Is that why C is incorrect?
Please help me out.
Thanks

This is a K & B book example, from chap:7, page620.




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.


Answer:
B, E, and F are correct.
 
Java Cowboy
Posts: 16084
88
Android Scala IntelliJ IDE Spring Java
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Sue, please check your private messages. You can see them by clicking My Profile.
 
Jesper de Jong
Java Cowboy
Posts: 16084
88
Android Scala IntelliJ IDE Spring Java
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
"Sue M" - please have a look at your private messages again.
 
Can't .... do .... plaid .... So I did this tiny ad instead:
the value of filler advertising in 2021
https://coderanch.com/t/730886/filler-advertising
reply
    Bookmark Topic Watch Topic
  • New Topic