[Biojava-dev] another 1.5 generics question

[Matthew Pocock]

I have had trouble with some cases of nesting templated declarations 
like this, particularly with anonymous classes. It is a particular 
instance of Graph that is parameterised by concrete types in place of A 
and B. Node and Edge do not have an instance of Graph available, so they 
can not infer the run-time type  of A and B. Try making the Node and 
Edge interfaces non-static. Alternatively, it may be possible to declare 
Node and Edge as being parameterised by AA and BB, and swapping the 
types appropreately in their deffinitions.

Matthew

Michael Heuer wrote:

>All,
>
>Sorry to abuse the list with another 1.5 generics question.
>
>Given,
>
>import java.util.Map;
>import java.util.Set;
>
>/**
> * A graph.
> */
>public interface Graph<A, B>
>{
>
>    /**
>     * Return a read-only set view of the nodes in this graph.
>     */
>    Set<Node<A>> nodes();
>
>    /**
>     * Return a read-only set view of the edges in this graph.
>     */
>    Set<Edge<B>> edges();
>
>    /**
>     * Return a map of type <code>&lt;Node, T&gt;</code> with
>     * the nodes in this graph as keys.
>     */
>    <T> Map<Node, T> nodeMap();
>
>    /**
>     * Return a map of type <code>&lt;Edge, T&gt;</code> with
>     * the edges in this graph as keys.
>     */
>    <T> Map<Edge, T> edgeMap();
>
>    /**
>     * Create a node in this graph for the specified element
>     * (optional operation).
>     */
>    Node<A> createNode(A a)
>        throws UnsupportedOperationException;
>
>    /**
>     * Create an edge in this graph for the specified element
>     * connecting the specified set of nodes (optional operation).
>     */
>    Edge<B> createEdge(B b, Set<Node<A>> nodes)
>        throws UnsupportedOperationException;
>
>
>    /**
>     * Node in a graph.
>     */
>    interface Node<A>
>    {
>
>        /**
>         * Return the element at this node.
>         */
>        A get();
>
>        /**
>         * Set the element at this node to <code>a</code>
>         * (optional operation).
>         */
>        void set(A a)
>            throws UnsupportedOperationException;
>
>        /**
>         * Return a read-only set view of the edges in this graph connected
>         * to this node.
>         */
>        Set<Edge<B>> edges();
>    }
>
>
>    /**
>     * Edge in a graph.
>     */
>    interface Edge<B>
>    {
>
>        /**
>         * Return the element at this edge.
>         */
>        B get();
>
>        /**
>         * Set the element at this edge to <code>b</code>
>         * (optional operation).
>         */
>        void set(B b)
>            throws UnsupportedOperationException;
>
>        /**
>         * Return a read-only set view of the nodes in this graph connected
>         * by this edge.
>         */
>        Set<Node<A>> nodes();
>    }
>}
>
>I get a complaint about the Set<Edge<B>> edges() method on
>Node<A> and the Set<Node<A>> nodes() method on Edge<B>:
>
>  non-static class A cannot be referenced from a static context
>
>I'm a bit confused, because I thought that everything is static in an
>interface definition, and I thought that A, B in this example are just
>type placeholders for the element classes.
>
>   michael
>
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>  
>