在java中创建树数据结构？

Creating a tree data structure in java?

提问by user2152012

I am trying to create a tree data structure in java where each parent node can have only three child nodes but I'm stuck on adding a node to the tree in the case where a node has at least one child but less than 3 child nodes. I'm unsure if I should use a Iterator to iterator through the list of nodes for the current node I'm on. I tryed to use a variable that would increment each time the add()method was called. here's my code: Node class:

我正在尝试在 java 中创建一个树数据结构，其中每个父节点只能有三个子节点，但是在节点至少有一个子节点但少于 3 个子节点的情况下，我坚持向树添加一个节点. 我不确定是否应该使用 Iterator 来遍历我所在的当前节点的节点列表。我尝试使用每次add()调用该方法时都会增加的变量。这是我的代码：节点类：

public class Node {

    int keyValue;
    int nodeLabel;
    ArrayList<Node> nodeChildren;

    private static int count;

    Node(int _keyValue)
    {
        this.nodeLabel = count;
        this.keyValue = _keyValue;
        this.count++;
        nodeChildren = new ArrayList<Node>();
    }

    public String toString()
    {
        return "Node " + nodeLabel + " has the key " + keyValue;
    }

}

Tree class: add()method

树类：add()方法

Node rootNode;
    int incrementor = 0;

    public void addNode(int nodeKey)
    {
        Node newNode = new Node(nodeKey);

        if (rootNode == null)
        {
            rootNode = newNode;
        }
        else if (rootNode.nodeChildren.isEmpty())
        {

            rootNode.nodeChildren.add(newNode);
        }
        else if (!rootNode.nodeChildren.isEmpty())
        {
            Node currentNode = rootNode;
            Node parentNode;
            incrementor = 0;

            while (currentNode.nodeChildren.size() < 3)
            {
                //currentNode.nodeChildren.add(newNode); 
                if (currentNode.nodeChildren.size() == 3)
                {
                    parentNode = currentNode.nodeChildren.get(incrementor);
                    currentNode = parentNode;
                    currentNode.nodeChildren.get(incrementor).nodeChildren.add(newNode);
                }
                else
                {
                    parentNode = currentNode;
                    currentNode = currentNode.nodeChildren.iterator().next();
                    currentNode.nodeChildren.add(newNode);

                }
                incrementor = incrementor + 1;
            }
            System.out.println(rootNode.nodeChildren.size());
        }
    }

I get a IndexOutOfBounds exception when a third node is added to tree

当第三个节点添加到树时，我收到 IndexOutOfBounds 异常

回答by C.B.

while (currentNode.nodeChildren.size() < 3)

will cause

将造成

if (currentNode.nodeChildren.size() == 3)

to always evaluate to false, thus the parent node will never switch to a child.

总是评估为假，因此父节点永远不会切换到子节点。