试图通过在子类中扩展类来向类添加方法？

（TL;DR：跳到粗体。）

我试图建立一个修改过的九头蛇的计算机模拟——在这个版本中，每个九头蛇头可以有更多的九头蛇头从中出来。我觉得这很像节点，所以我首先构建了一个通用Node类。每个Node对象都有一个ArrayList<Node>of children，每个对象（也是一个Node）都可以有自己的children。

Hydra 的头部结构与 相同Node，但行为不同。（例如。ANode应该能够简单地移除它的孩子，而从 Hydra 中移除一个头还需要重新长出一些头。）所以我构建HydraNode extends Node并添加了类似的方法cutHead()（它移除了一个头（节点），然后添加了克隆）。AHydra是“身体”，有HydraNodes 代表头部。

问题是，因为所有的子节点都存储为一个ArrayList<Node>，我可以做

Hydra hydra = new Hydra(1,1,1) // Makes a Hydra with 3 levels (1 head, which has 1 head, which has 1 head).
Node nodeAtLevel1 = hydra.getChildren.get(0); // Has to be declared as Node, not HydraNode, because getChildren() is a Node method, and returns an ArrayList<Node> of children.

，但它的每个子节点实际上都是节点。这导致了 中的问题main()，我尝试运行nodeAtLevel1.cutHead()但不能，因为cutHead()是一种HydraNode方法。

在对象包含自身的情况下，如何向类添加功能？将对象扩展到 asubclass似乎不起作用，因为检索包含的对象将返回类型为 的对象superclass，而不是subclass。我不能把它向下抛。我能做什么？

节点.java

public class Node {
    // Member variables
    private ArrayList<Node> children = new ArrayList<>(); // Holds "children" nodes.
    private int hierarchyLevel; // Where in the hierarchy is it?
    private int childCount = 0; //How many "child" nodes does this node have?

    // Constructors
    public Node(int hierarchyLevel) {this.hierarchyLevel = hierarchyLevel}
    public Node(int hierarchyLevel, int... nodesPerLevel) {this(hierarchyLevel;} //Adds children to this node, eg. {1,2,1} adds 1 child node at lvl 1, 2 children at lvl 2, each with 1 child of their own at level 3.

    // Methods
    public ArrayList<Node> getChildren() {return children;}
    public void addChild() {} // Adds a child directly to this node
    public void removeChild(int i) {}

    public Node getCopy() {} //Returns a clone of this Node and all its child nodes.

    public String toString() {} // Eg. Node at Level ___ has ____ children.

}

HydraNode.java（头部）

public class HydraNode extends Node {
    // Constructors
    public HydraNode(int hierarchyLevel) { // Just call super, bc this is essentially a Node structure that just acts a little differently.
        super(hierarchyLevel);
    }
    public HydraNode(int hierarchyLevel, int... nodesPerLevel) {
        super(hierarchyLevel, nodesPerLevel);

    // Methods
    public void cutHead() {} // Cutting a Level 1 head, which is attached to the body (level 0), does not regrow. However, any other cut will multiply that branch's parent x3.
}

九头蛇

public class Hydra {
    // MAIN method
    public static void main(String[] args) {
        Hydra hydra = new Hydra(1,1,1);
        Node head2 = hydra.body.getChildren().get(0).getChildren().get(0);
        System.out.println(head2.toString()); // >> Node at Level 2 has 1 child node.
        //head2.cutHead(); // Doesn't work because cutHead() is a HydraNode method, not a Node method.
    }

    // Member Variables
    public static int regrowFactor = 2; // Every time a head is cut off, the hydra clones the remaining branches. In the original video, the hydra forms two new clones.
    HydraNode body;

    // Constructors
    public Hydra() {
        body = new HydraNode(0); // the body is just a new Node at level 0
    }
    public Hydra(int... headsPerLevel) {
        body = new HydraNode(0, headsPerLevel);
    }
}