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所以我设计了一个二叉搜索树类。在老师的指导下，树不是由节点组成，而是由其他二叉树组成——它的孩子是通过插入新的二叉树来创建的。我们需要创建一个 Counter 类，它是树大小变化的观察者，我们需要计算“节点”的数量但我不知道如何在每次插入调用时通知...b/ c 如果我通知创建一棵新树——我的“nodeCount”每次在构造函数中都会被重置……有什么想法吗？

这是我的 BST 课

    package model;
    import java.util.*;

    public class BinaryTree extends Observable{

Strategy strategy;

int value;
BinaryTree leftChild;
BinaryTree rightChild;

int size;


BinaryTree(){
    value = -1;
    leftChild = null;
    rightChild = null;
}

public BinaryTree(int newValue){
    this.value = newValue;
}

public int getValue(){ return value;}

public Boolean isEmpty(){
    Boolean isEmpty;
    if(this == null)
        isEmpty = true;
    else
        isEmpty = false;
    return isEmpty;
}


public void insert(int newValue){
    if(value == -1){
        this.value = newValue;
        size = 1;
        setChanged();
        notifyObservers(new Integer(size));
        clearChanged();
    }
    else if(newValue < this.value){
            if(leftChild != null){
                leftChild.insert(newValue);
            } else {
                System.out.println("Inserted " + newValue + " to the left of " + value);
                leftChild = new BinaryTree(newValue);
                size = size + 1;
                setChanged();
                notifyObservers(new Integer(size));
                clearChanged();
            }
    } else if (newValue >= this.value){
        if(rightChild != null){
            rightChild.insert(newValue);
        } else {
            System.out.println("Inserted " + newValue + " to the right of " + value);
            rightChild = new BinaryTree(newValue);
            size = size + 1;

            setChanged();
            notifyObservers(new Integer(size));
            clearChanged();
        }
    }

}

}

这是我的柜台课

    package model;
    import java.util.*;

    public class Counter implements Observer{
private int size;
public Counter(){
    size = 0;
    System.out.println("Counter created: Size is " + size);
}

public void update(Observable BinaryTree, Object size){
    if(size instanceof Integer){
        size = ((Integer)size).intValue();
        System.out.println("Counter : Size changed to " + size);
    } else {
        System.out.println("Counter: Some other change to the tree");
    }
}

}

这是一些示例输出......一旦创建了新树，计数器就会消失 - 我想我理解这个问题我只是不知道如何解决它......我尝试使用委托观察者，但这只是混淆我更……有什么建议吗？

Please enter as many integers as you'd like, hit 'Q' when you are finished.

2
Counter : Size changed to 1
4
Inserted 4 to the right of 2
Counter : Size changed to 2
3
Inserted 3 to the left of 4
5
Inserted 5 to the right of 4
4
Inserted 4 to the left of 5
5
Inserted 5 to the right of 5

这是主要方法

    package model;
    import java.io.*; 
    import java.util.*; 


    public class menu {
public static void main(String[] args){
    int integerInput;
    int inputOption;

    BinaryTree myIntTree;
    myIntTree = new BinaryTree();

    Counter sizeObs = new Counter();
    myIntTree.addObserver(sizeObs);


    Scanner userInput = new Scanner(System.in);
    do{

    System.out.println("=======================================");
    System.out.println("     Binary Search Tree Traversal!     ");
    System.out.println("=======================================");
    System.out.println("Options:                               ");
    System.out.println("  1.  Create a new binary search tree  ");
    System.out.println("  2.  Quit                             ");
    System.out.println("=======================================");

    inputOption = KeyIn.inInt("Please select an option from the menu: ");

    switch(inputOption){
        case 1:
            System.out.println("You've selected to create a new binary tree." + "\n");
            Scanner scan = new Scanner(System.in);
            //String again;
            String tempInput;
            Boolean repeat = true;
            try{
                System.out.println("Please enter as many integers as you'd like, hit 'Q' when you are finished." + "\n");
                do{

                    tempInput = scan.next();
                    if(!tempInput.equals("Q") && !tempInput.equals("q")){
                        integerInput = Integer.parseInt(tempInput);
                        myIntTree.insert(integerInput);
                        repeat = true;
                    }
                    else
                        repeat = false;

                }while(repeat);

            }catch(InputMismatchException e){}

        break;

        case 2:

            System.out.println("Goodbye!");
            break;
        default:
            System.out.println("Invalid selection.");
            break;              
    }
}while(inputOption != 2);
}

}

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1 回答 1

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据我了解，您正在尝试跟踪主树（起源于主根的树）。但是您应该知道，某些插入是针对此主树的子树（即属于大/主树的节点之一）进行的。

您不会“观察”这些节点（子树）。每次创建新节点时，例如：

 leftChild = new BinaryTree(newValue);

您还应该将其添加为观察者（即 Counter 实例）。

问题是，这样一来，您将为每棵树都有一个观察者，并且它们中的每一个都将跟踪不同size的，即该树的大小实例变量。

您应该在插入新树时应该更新size的类中使用类变量。BinaryTree这样所有的计数器都将跟踪相同大小的变量。

于 2012-08-05T22:11:49.543 回答