无法将实现传递给声明通用接口（Java）的方法

Question

Two attempts at passing in my generic class in the MyTest class below. The Strategy hierarchy seems fine, but declaring methods with the generic interface as an argument has problems. How do I resolve this?

interface Node {}

class NodeImpl implements Node {}

interface Strategy <N extends Node> {

    void setNode(N node);

}

class MyStrategy implements Strategy<NodeImpl> {

    @Override
    public void setNode(NodeImpl node) {
    }

}

class MyTest {

    void test1(Strategy<? extends Node> s) {
        s.setNode(new NodeImpl()); // compile error
    }

    void test2(Strategy<Node> s) {
        s.setNode(new NodeImpl());
    }

    void v() {
        test1(new MyStrategy());
        test2(new MyStrategy()); // compile error
    }
}

Test1 compile error: The method setNode(capture#1-of ? extends Node) in the type Strategy is not applicable for the arguments (NodeImpl)

Test 2 compile error: The method test2(Strategy) in the type MyTest is not applicable for the arguments (MyStrategy)

The MyTest class is part of an inheritance hierarchy, I wish to keep the test1() or test2() method generic, being able to pass in any Strategy implementation

Answer 1

test1 and test2 can compile if you use NodeImpl instead of Node (generics is strongly typed). About Test1, as per Marko suggestion, you should use Strategy <? super NodeImpl> Strategy <? super NodeImpl> into method signature.

Answer 2

This appears to solve the problem, but it's a bit clunky. I'm also interested in any design comments within the scope of this example code.

interface Node {}

class NodeImpl implements Node {}

interface Strategy <N extends Node> {

    void setNode(N node);

    Class<N> getType();
}


class MyStrategy implements Strategy<NodeImpl> {

    @Override
    public void setNode(NodeImpl node) {
    }

    @Override
    public Class<NodeImpl> getType() {
        return NodeImpl.class;
    }
}

class MyTest {

    <T extends Node> void test3(Strategy<T> s) {    
        s.setNode(s.getType().cast(new NodeImpl()));
    }

    void v() {
        test3(new MyStrategy());
    }
}