java - Java中如何检查ArrayList树是否为空？

Question

我正在用 Java 创建一棵树。当我创建一个方法来检查树是否为空时，它无法正常工作。当我调试程序并进入检查 root 是否为空的 if 语句时，我不断收到“parent = null”。我认为问题可能是由于父集方法造成的，但我不确定。这是我的代码:

{
    private Tree data = null; //create a tree
    private List<GeneralTree> children = new ArrayList<>(); //create an arraylist
    private GeneralTree parent = null; //create a parent
    public GeneralTree(Tree data) //constructor
    {
        this.data = data;
    }
    public void addChild(GeneralTree child) //create a child method to create a child
    {
        child.setParent(this);
        this.children.add(child);
    }
    public void addChild(Tree data) //create a method to put data into the children
    {
        GeneralTree<Tree> newChild = new GeneralTree<>(data);
        this.addChild(newChild);
    }
    public void addChildren(List<GeneralTree> children) //create a method to add children to a parent
    {
        for(GeneralTree t: children)
        {
            t.setParent(this);
        }
        this.children.addAll(children);
    }
    public List<GeneralTree> getChildren() //get the children
    {
        return this.children;
    }
    public Tree getData() //get the data in the children
    {
        return data;
    }
    public void setData(Tree data) //set the data of the children together
    {
        this.data = data;
    }
    public void setParent(GeneralTree parent) //set the parent together
    {
        this.parent = parent;
    }
    public GeneralTree getParent() //get the parent
    {
        return this.parent;
    }

我遇到问题的 Main isEmpty() 方法

    public boolean isEmpty()
    {
        if(this.parent == null) //check if value is null. if it is true, the tree is full.
        {
            System.out.println("The tree is empty.");
            return false;
        }
        else
        {
            return true;
        }
    }

驱动类的主要方法

    public static void main(String[] args)
    {
        GeneralTree<String> root = new GeneralTree<>("Root"); //create a root node

        if(root.isEmpty())
        {
            if(true)
            {
                System.out.println("The tree is empty.");
            }
        }
        GeneralTree<String> child1 = new GeneralTree<>("Child 1"); //first child node
        child1.addChild("Grandchild 1"); //first grandchild node
        child1.addChild("Grandchild 2"); //second grandchild node
        GeneralTree<String> child2 = new GeneralTree<>("Child 2"); //second child node
        child2.addChild("Grandchild 3"); //third grandchild node
        root.addChild(child1);
        root.addChild(child2);
        root.addChild("Child 3"); //third child node
        root.addChildren(Arrays.asList(new GeneralTree<>("Child 4"), new GeneralTree<>("Child 5"), new GeneralTree<>("Child 6")));//add fourth, fifth, and sixth children nodes
        for(GeneralTree node: root.getChildren()) //get and print the children as long as they're under the root
        {
            System.out.println(node.getData()); //get the data
        }
    }
}

不知道是父节点的问题还是isEmpty()方法的设计问题？

Answer 1

你的 isEmpty() 方法对我来说似乎没有意义。

它询问父级是否为空。这和空有什么关系？

“父项是否为空？”意思是“我是根吗？”。

或者换句话说 - 根永远没有父级，因此根据您的测试， root.isEmpty() 永远为真。

按照我的思维方式，“空树”意味着“没有子节点”(如果可能的话，“这里没有数据”)。