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POFitting in Java Generics for this specific use scenario
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19402333
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2013-10-16T11:35:10.313
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2013-10-16T12:32:30.120
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2013-10-16T11:40:53.557
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First of all sorry for the not very specific title, but i couldn't find a better and short descriptive one! I've got an Interface like so: <pre><code>public interface ModelInterface { public List<? extends Umbrella> getBRs(); } </code></pre> And and several implementing classes of this pattern: <pre><code>public class Model implements ModelInterface { // need to use the concrete impl here because of JPA List<StoneUmbrella> _list = new ArrayList<>(); @Override public List<? extends Umbrella> getBRs() { return _list; } } </code></pre> So far so good. But i also have the following Util class: <pre><code>import java.util.Collection; public abstract class Util<E, R> { public R reduce(Collection<E> collection, R initialElement) { R result = initialElement; for (E currElement : collection) { result = reduce(result, currElement); } return result; } abstract R reduce(R initialElement, E element); } </code></pre> Now the problem occurrs when i try to invoke that Utility class in my main code: <pre><code>import java.util.List; public class Main { public static void main(String[] args) { ModelInterface model = new Model(); List<? extends Umbrella> list = model.getBRs(); Util<Umbrella, Boolean> util = new Util<Umbrella, Boolean>() { @Override Boolean reduce(Boolean initialElement, Umbrella element) { return Boolean.TRUE; } }; util.reduce(list, Boolean.FALSE); } } </code></pre> The util.reduce line fails to compile with this message: The method reduce(Collection, Boolean) in the type Util is not applicable for the arguments (List<capture#2-of ? extends Umbrella>, Boolean) It works when i use List<Umbrella> instead of List<? extends Umbrella> but i can't change that in the Model Interface or i won't be able to return its internal list in the getter. I kind of think it's impossible to implement it in a way that satisfies both sides. Can anyone help? Thanks in advance!!
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<java><generics>
Title
Fitting in Java Generics for this specific use scenario
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