bounded-wildcard Questions
2
Solved
I have a relatively simple looking problem that I am trying to solve. There doesn't seem to be an intuitive way to do this or, I am missing something here.
Consider this method to find the main im...
Infidel asked 24/4, 2015 at 22:41
2
Solved
Assume class B inherits from class A. The following is legal Java:
List<A> x;
List<? super B> y = x;
In terms of the specification, this means that List<A> assignsTo List<? ...
Fistic asked 24/4, 2015 at 20:39
2
Solved
The following class defines two methods, both of which intuitively have the same functionality. Each function is called with two lists of type List<? super Integer> and a boolean value which ...
Dawnedawson asked 11/1, 2014 at 17:44
2
Solved
The following statements:
URLClassLoader ucl = (URLClassLoader) ClassLoader.getSystemClassLoader();
Class<URLClassLoader> uclc = ucl.getClass();
fail with error:
Type mismatch: cannot con...
Mixedup asked 9/6, 2014 at 8:11
2
Solved
Why is it that Java can infer the common ancestor of multiple upper-bounded types, but not of lower-bounded types?
More specifically, consider the following examples:
static class Test {
static...
Barolet asked 26/12, 2014 at 4:34
2
Why is this code valid
ArrayList<?>[] arr = new ArrayList<?>[2];
but the following two are not?
ArrayList<? extends Object>[] arr = new ArrayList<? extends Object>[2];
A...
Defer asked 1/10, 2014 at 10:54
4
Solved
Simple class:
class Pair<K,V> {
}
And a few assignments:
Collection<Pair<String,Long>> c1 = new ArrayList<Pair<String,Long>>();
Collection<Pair<String,Long&...
Lauralauraceous asked 14/7, 2014 at 13:28
2
Solved
(If this is a duplicate please point me to the right answer! I searched and read several (>5) related questions but none seemed on the mark. Also looked at the Generics FAQ and other sources...)
I...
Assonance asked 4/7, 2014 at 0:55
2
Solved
The following compiles just fine in JDK8, but gives an incompatible types error with JDK7.
List<List<? extends Number>> xs = Arrays.asList(Arrays.asList(0));
According to this answer...
Geneviegenevieve asked 12/6, 2014 at 15:56
4
Solved
I have the following two interfaces:
/**
* A marker interface to denote that an object implements a view on some other object.
*
* @param <T> The type of object that is viewed
*/
public ...
Coenosarc asked 29/4, 2014 at 12:16
2
Solved
How come one must use the generic type Map<?, ? extends List<?>> instead of a simpler Map<?, List<?>> for the following test() method?
public static voi...
Consolidate asked 2/4, 2014 at 8:54
2
Suppose I have a method "mix" that takes two Lists of possibly different types T and S and returns a single List containing the elements of both. For type-safety, I'd like to specify that the retur...
Jadejaded asked 18/8, 2013 at 21:12
4
I wonder why does this piece of code compile successfully?
Source code:
abstract class A<K extends Number>
{
public abstract <M> A<? super M> useMe(A<? super M> k);
}
C...
Pantile asked 23/12, 2013 at 23:32
4
Solved
So I am reading about generic method and I am get confused. Let me state the problem here first:
In this example: Suppose that I need a version of selectionSort that works for any type T, by using...
Dover asked 10/12, 2013 at 15:3
1
Solved
When I try to compile the following code:
LinkedList<List<? extends Number>> numList = new LinkedList<List<Integer>>();
I get an incompatible type error:
Required: Linke...
Exorbitant asked 25/11, 2013 at 22:40
2
Solved
I want to have a Class object, but I want to force whatever class it represents to extend class A and implement interface B.
I can do:
Class<? extends ClassA>
Or:
Class<? extends Inte...
Multiple asked 13/4, 2009 at 23:21
1
I am wondering what is wrong with this code:
Map <? extends String, ? extends Integer> m = null;
Set<Map.Entry<? extends String, ? extends Integer>> s = m.entrySet();
The compi...
Fairminded asked 20/9, 2013 at 0:51
2
Solved
Suppose I have this in Java:
List<String> list = new ArrayList<String>();
list.getClass();
The type of the last expression is Class<? extends List>. I understand why, due to er...
Babin asked 13/9, 2013 at 9:31
3
Solved
I am trying to read and understand some Java code. Here it is:
protected LoadTarget<? super PopulationLoadContext> createTarget(PopulationLoadContext context) {
return createTransacti...
Amazon asked 24/7, 2013 at 22:30
2
Solved
Why do the utility factory methods often use a specific generic parameter (like T) instead of a bounded wildcard parameter (like ? super T)?
For instance, the signature of Functions#forPredicate i...
Calendre asked 31/1, 2013 at 17:11
6
Solved
Is there ever a difference between an unbounded wildcard e.g. <?> and a bounded wildcard whose bound is Object, e.g. <? extends Object>?
I recall reading somewhere that there was a dif...
Book asked 6/1, 2010 at 20:33
3
I'm having trouble understanding why I can use bounded wildcards like this, if I can't (seem to) make any (genericly-typed) use of it.
If I have a wildcard field in a class, I can't use any of the...
Jovanjove asked 12/1, 2013 at 15:55
2
Solved
I'm stuck trying to translate some Java code that uses (bounded) wildcard generics to C#. My problem is, Java seems to allow a generic type to be both covariant and contravariant when used with a w...
Arenaceous asked 12/1, 2013 at 2:16
1
Solved
I'm stuck trying to translate some Java code that uses (bounded) wildcard generics to C#.
My problem is, Java seems to allow a generic type to be both covariant and contravariant when used with a ...
Caryloncaryn asked 11/1, 2013 at 11:40
1
class Aliphatic<F> extends Organic<F>{}
class Hexane<G> extends Aliphatic<G>{}
public class Organic<E>{
void react(E e){}
static void main(String[] args){
Organic&l...
Brigandine asked 15/10, 2012 at 14:54
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