Generic code help

[Deepa Sreedhara]

import java.util.*;
public class Genex3 {
public static void main(String[] args) {
List<? extends Number>	sList = new ArrayList(); //(1)
int i = 2007;
sList.add(i);
sList.add(new Integer(11)); //(2)
//sList.add(30.5);
Integer num = (Integer)sList.get(0); //(3)
}
}

Is it because of '? extends ' instead of '? super' expression, the compiler wont let me add anything to the list. The code is from Khalid Mudgal book, a bit tweaked by me.

[Heena Agarwal]

Is it because of '? extends ' instead of '? super' expression, the compiler wont let me add anything to the list.

Yes.
But it's important to understand why. I suggest you go through the following post also

https://coderanch.com/t/627111/java-programmer-SCJP/certification/difference-List-super-Dog-animals#2869356

and try to understand the question and the responses. I think that might give you more clarity.

[Rico Felix]

Have a look at this post