霍夫曼编码不使用频率

Question

我在不使用频率的情况下构建huffmanTree时遇到问题，用户将直接输入字符和二进制数给huffmanTree。根据用户输入，如果二进制的第一个输入是0，它应该向左，如果它是1，它应该向右。当插入第二个二进制代码时，程序应检查该位置是否为叶子。如果是叶子，请插入。如果没有返回该地点的消息。

我想出了一个回复错误的想法。

线程“main”java.lang.NullPointerException中的异常     在ideas.ideas.insert（ideas.java:70）

import java.util.LinkedList;
import java.util.Scanner;


  class Node {

    char data;
    int idata;
    boolean isCreated = false;
    Node leftChild, rightChild;

    public Node(char data) {
        this.data = data;
        leftChild = new Node();
        rightChild = new Node();
    }

    public Node() {
    }

}


public class ideas{

    Node root = new Node();

    public ideas(){

        root.isCreated = true;

    }

    void insert(char data, String bin) {
        Node newNode = new Node();
        newNode.isCreated=true;

        if (!root.isCreated) {
            System.out.println("It never enters here, since the root is always empty and is created with the constructor ");
            root = newNode;
            root.isCreated = true;
        } else {
            System.out.println(""); 
            Node current = root;
            Node parent = current;
            int i = 0;

            while (i < bin.length()) {

                parent = current;
                if (bin.charAt(i) == '0') {
                    System.out.println("Parent leftChild is : "+newNode.isCreated);
                    current = current.leftChild;
                   // System.out.println("Current left child is : "+current.isCreated);
                           if (current.isCreated == false) {

                        parent.leftChild = newNode;
                        current.isCreated = true;
                        // current.idata = 0;
                        //return;
                        i++;
                    }
                } else {
                    current = current.rightChild;


                    if (current.isCreated == false) {
                        parent.rightChild = newNode;
                        current.isCreated = true;
                        //current.idata = 1;
                        //return;
                        i++;
                    }
                }
            }

            current.data = data;
             System.out.println("the data is "+current.data);
        }
    }

    void preOrder(Node current) {
        if (current.isCreated == false) {


                System.out.println(current.data);

            preOrder(current.leftChild);
            preOrder(current.rightChild);

        }

    }

    public static void main(String[] args) {
        System.out.println("Enter a character");
        System.out.println("Enter its binary code");
        ideas t = new ideas();
        t.insert('e', "10101");
    //    t.insert('a', "00101");
        t.preOrder(t.root);

    }

}