This week's book giveaways are in the Refactoring and Agile forums.
We're giving away four copies each of Re-engineering Legacy Software and Docker in Action and have the authors on-line!
See this thread and this one for details.
Win a copy of Re-engineering Legacy Software this week in the Refactoring forum
or Docker in Action in the Cloud/Virtualization forum!
  • Post Reply
  • Bookmark Topic Watch Topic
  • New Topic

Generic Question

 
Sagar Shroff
Ranch Hand
Posts: 209
Java Tomcat Server
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
[b]
[/b]
Can some one make me explain why this is not compiling.The compiler is telling me that Parameter is not within Bounds......

Also not understanding then how this is working ??
[b]
[/b]

Please Help me ??

Examples would be really appreciated !!

Can someone please help me with an example of my 2 Questions ??
 
Ankit Garg
Sheriff
Posts: 9509
22
Android Google Web Toolkit Hibernate IntelliJ IDE Java Spring
  • Likes 2
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator

In this case you are declaring a new K with your method declaration. Basically the code is equivalent to this code

Now here M might be resolved to something not compatible with Number, like lets say String. But Test class can only have a type which is a Number. So you'll have to bound M to a number.


Here first of all the type declaration in the method is useless. So we'll strip it out first

Now the return type would clearly work. As for the parameter, since you are using a wildcard syntax, so compile would be able to maintain type safety here. Lets actually put some code into the class to see how

Basically you can't make changes to s variable based on its type as the type is not known. So even though ? super K seems to be breaking the bounds of K, it will still result in type safe code which is the goal of generics...
 
Sagar Shroff
Ranch Hand
Posts: 209
Java Tomcat Server
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Thanks Ankit !!
 
  • Post Reply
  • Bookmark Topic Watch Topic
  • New Topic