interface Item() {
    String getName();
    void setName(String name);
}

interface ParentItem extends Item {
    Child[] getChildren();
    void setChildren(Child[]);
}

interface Child extends Item {
    Parent getParent();
    void setParent(Parent parent);
}

class Root implements Parent {
    // implementation
}

class Node implements Parent, Child {
    // implementation
}

class Leaf implements Child {
    // implementation
}