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A quanstion about generics
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Posted: Oct 17, 2008 7:50 PM
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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.
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