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所以，我有 this public interface NodeLevel<E extends NodeLevelEnum>，它有方法public E getParent()和public E getEnum(). 一个实现abstract public class NodeLevelAbstract<E extends NodeLevelEnum> implements NodeLevel<E>委托到实现的类的A实例public interface NodeLevelEnum<E extends NodeLevelEnum>。最后一个声明应该意味着实现类的实例NodeLevelEnum可以对实现类的实例做一些事情NodeLevelEnum。

现在，这是NodeLevelAbstract#getParent()：

@Override
public E getParent() {
    return this.getEnum().getParent();
}

导致编译器错误（我使用 NetBeans 7.2，顺便说一句）：

incompatible types
required: E
found:    NodeLevelEnum
where E is a type-variable:
E extends NodeLevelEnum declared in class NodeLevelAbstract

对我来说，这意味着 的后代NodeLevelEnum是必需的，但NodeLevelEnum被发现了，鉴于 Java 泛型中的边界包括自身，这听起来像是胡说八道。

为什么这些类型不兼容？有什么优雅的方式来做我想做的事吗？提前致谢。=)

更新 1

顺便说一句，NodeLevelEnum#getParent()返回<E extends NodeLevelEnum>，而不是NodeLevelEnum，错误说它确实如此。

更新 2

abstract public class NodeLevelAbstract<E extends NodeLevelEnum> implements
        NodeLevel<E> {

    protected E _enum;

    @Override
    public E getEnum() {
        return this._enum;
    }

    @Override
    public E getParent() {
        return this.getEnum().getParent();
    }

    public static <E extends NodeLevelEnum<E>> E[] getEnumLineage(E _enum) {
        ArrayList<E> ancestors = new ArrayList<>();
        E currentEnum = _enum;
        do {
            ancestors.add(currentEnum);
            currentEnum = currentEnum.getParent();
        } while (currentEnum != null);
        return (E[]) ancestors.toArray();
    }

    public static <E extends NodeLevelEnum<E>> HashMap<String, String>
        getEnumLineageValueMap(
            E _enum) {
        HashMap<String, String> map = new HashMap<>();
        for (E e : getEnumLineage(_enum)) {
            map.put(e.getCode(), e.getValue());
        }
        return map;
    }
}

public interface NodeLevel<E extends NodeLevelEnum> {

    public E getEnum();

    public E getParent();
}

public interface NodeLevelEnum<E extends NodeLevelEnum> {

    public E getParent();
}

public interface FilestructureLevel<E extends NodeLevelEnum<E>> extends
        NodeLevel<E> {

    public String getPathPrefix();
}

public class FileLevel<E extends NodeLevelEnum<E>> extends NodeLevelAbstract<E>
        implements FilestructureLevel<E> {

    protected String _pathPrefix;

    @Override
    public String getPathPrefix() {
        return this._pathPrefix;
    }

    public HashMap<String, String> getValueMap(Boolean withPath) {
        return getEnumLineageValueMap(this.getEnum(), withPath);
    }

    public static <E extends NodeLevelEnum<E>> HashMap<String, String>
        getEnumLineageValueMap(
            E _enum) {
        return getEnumLineageValueMap(_enum, false);
    }

    public static <E extends NodeLevelEnum<E>> HashMap<String, String>
        getEnumLineageValueMap(
            E _enum, Boolean withPath) {
        HashMap<String, String> map = new HashMap<>();
        FileLevelEnum[] lineage = (FileLevelEnum[]) getEnumLineage(_enum);
        for (FileLevelEnum e : lineage) {
            String value = !withPath ? e.getValue() : e.getPathPrefix()
                + e.getValue();
            map.put(e.getCode(), value);
        }
        return map;
    }
}
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