Java:接口(interface)和泛型的简单问题

Question

我制作了一个与 JGraphT 一起使用的界面。我的预期用途类似于 Comparable，因为实现 Comparable 允许对象与某些数据结构一起使用。同样，我有一个 JGraphT 函数，我想使用它来处理任何 Distanceable 的东西。

public interface Distanceable<E> {

    /**
     * A representation of the distance between these two objects.
     * If the distance between a0 and a1 is undefined, <code>a0.hasEdge(a1)</code> should return false;
     * @param o
     * @return
     */
    public int distance(E o);

    /**
     * Are these two objects connected?
     * @param o
     * @return True if the two objects are connected in some way, false if their distance is undefined
     */
    public boolean hasEdge(E o);
}

这是我在 JGraphtUtilities 中的 JGraphT 函数。它不是为 Animal 定义的，而是为 Distanceable 定义的:

public static <E extends Distanceable> WeightedGraph<E, DefaultWeightedEdge> graphOfDistances(Set<E> nodes) {
    WeightedGraph<E, DefaultWeightedEdge> g = new SimpleWeightedGraph<E, DefaultWeightedEdge>(DefaultWeightedEdge.class);

    for (E a : nodes) {
        g.addVertex(a);
    }

    for (E a : nodes) {
        for (E a1 : nodes) {
            if (a.hasEdge(a1)) {
                g.addEdge(a, a1);
                g.setEdgeWeight(g.getEdge(a, a1), a.distance(a1));
            }
        }
    }

    return g;
}

但是这不起作用。编译器在调用此方法的另一个类中的这一行产生错误:

WeightedGraph<Animal, DefaultWeightedEdge> graphOfAnimals = JGraphtUtilities.graphOfAnimals(zoo);

错误是:

The method graphOfAnimals(Set<Animal>) is undefined for the type JGraphtUtilities

但是，

public class Animal implements Distanceable<Animal> {

我在这里做错了什么？

另一个问题:编译器给出此警告:

Distanceable is a raw type. References to generic type Distanceable<E> should be parameterized.

如果我希望此函数适用于所有 Distanceable 对象，我想要给它什么类型？

Answer 1

The method graphOfAnimals(Set<Animal>) is undefined for the type JGraphtUtilities

您在代码示例中显示的方法是 graphOfDistances 。问题出在方法 graphOfAnimals 上。所以...

你有graphOfAnimals吗？需要 Set<Animal> 的方法在 JGraphtUtilities类？