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A quanstion about generics

1 reply on 1 page. Most recent reply: Jul 9, 2009 7:39 PM by Darko Latkovic

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Robinson Emmanuel

Posts: 1
Nickname: robinson
Registered: Oct, 2008

A quanstion about generics Posted: Oct 17, 2008 10:50 PM
Reply to this message Reply
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Here is an example in 'Thingking in Java 4e':

public class GenericWriting {
static <T> void writeExact(List<T> list,T item){
list.add(item);
}
static List<Apple> apples = new ArrayList<Apple>();
static List<Fruit> fruit = new ArrayList<Fruit>();
static void f1(){
writeExact(apples, new Apple());
// writeExact(fruit, new Apple()); // Error:
//Incompatible types:found Fruit,required Apple
}
static <T> void writeWithWildcard(List<? super T> list,T item){
list.add(item);
}
static void f2(){
writeWithWildcard(apples, new Apple());
writeWithWildcard(fruit, new Apple());
}

public static void main(String[] args) {
f1();
f2();
}
}

class Fruit{

}

class Apple extends Fruit{

}

Bruce Eckel said "writeExact(fruit, new Apple());" is an error,but I run it rightly,could somebody tell me why?
Thank you very much.


Darko Latkovic

Posts: 9
Nickname: darko
Registered: Jul, 2009

Re: A quanstion about generics Posted: Jul 9, 2009 7:39 PM
Reply to this message Reply
Works fine for me as well. My Java version is 1.6.0_13.
Maybe it was an issue with some previous versions.

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