txt中自个儿敲入字符，程序就会报错

package Bbstree;

import java.io.*;
import java.util.HashMap;
import java.util.Map;
public class Tree {

	TreeNode trnode[];
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		String allword=null,buffword; //保存单个单词
		String sentense[]=null;//读取整个字符串，tree用来实现二叉树
		int length,a,dep=0;
		TreeNode tnodebuf,thead;
		try
		{
			String encoding="UTF-8";
			File file = new File("D://test_2.txt");    //file 指向目录中的文件
			if(file.isFile() && file.exists())
			{ //判断文件是否存在
		           InputStreamReader read = new InputStreamReader(new FileInputStream(file),encoding);//考虑到汉子编码格式		          
		           BufferedReader br =new BufferedReader(read);		       
		           allword=br.readLine();    //读取文件中的一行数据
		           length=allword.length();    //获得字符串s1的长度并赋值给length_1	
		           read.close();
			}
			
			else{
				   System.out.println("找不到指定的文件");
				}
		}
		catch(Exception e){
			System.out.println("读取文件内容出错");
			e.printStackTrace();
		}
		if(allword!=null)
		{
			sentense=allword.split(" ");
		}
		TreeNode trnode[]=new TreeNode[sentense.length];
		for(int i=0;i<sentense.length;i++)
		{
			trnode[i]=new TreeNode(sentense[i]);
			
		}
		for(int i=0;i<sentense.length;i++)
			for(int j=0;j<sentense.length-i-1;j++)
			{
				if(trnode[j].length>trnode[j+1].length)
				{
					tnodebuf=new TreeNode(sentense[i]);
					tnodebuf.NodeCopy(trnode[j]);
					trnode[j].NodeCopy(trnode[j+1]);
					trnode[j+1].NodeCopy(tnodebuf);
				}
			}
		thead=new TreeNode();
		thead.pos=(0+sentense.length)/2;
		int depth=Creatbtree(trnode,0,sentense.length-1,0,sentense.length,dep);
		TreeNode netree[]=new TreeNode[sentense.length];
		for(int i=0;i<sentense.length;i++)
		{
			netree[i]=new TreeNode();	
		}
		int nelength=FindAcctimes(trnode,netree,sentense.length);
		wordsort(netree,nelength-1);
		fiwrite(netree,depth,nelength-1);
	}
//trnode保存二叉树，netree保存出现次数，以及去除了相同的字符串
	private static int Creatbtree(TreeNode trnode[],int pos1,int pos2,int i,int length,int dep)
	{	//递归简历平衡排序二叉树	
		int dep1,dep2;
			dep++;
			
			if(pos1<=pos2)
			{
				if(pos1==pos2)
				{
					trnode[(pos1+pos2)/2].lchild=-1;
					trnode[(pos1+pos2)/2].rchild=-1;
					trnode[(pos1+pos2)/2].pos=dep;
				}
				else if((pos1+pos2)/2==pos1)
				{
					trnode[(pos1+pos2)/2].lchild=-1;
					trnode[(pos1+pos2)/2].rchild=(pos2+(pos1+pos2)/2+1)/2;
					trnode[(pos1+pos2)/2].pos=dep;
				}
				else
				{
					trnode[(pos1+pos2)/2].lchild=(pos1+(pos1+pos2)/2-1)/2;
					trnode[(pos1+pos2)/2].rchild=(pos2+(pos1+pos2)/2+1)/2;
					trnode[(pos1+pos2)/2].pos=dep;
				}
				
				dep1=Creatbtree(trnode,pos1,(pos1+pos2)/2-1,i,length,dep);
				dep2=Creatbtree(trnode,(pos1+pos2)/2+1,pos2,i,length,dep);
				dep=((dep1>dep2)?dep1:dep2)>dep?((dep1>dep2)?dep1:dep2):dep;//得出深度
				
			
			}
			return dep;
	}
	private static int FindAcctimes(TreeNode trnode[],TreeNode treenode[],int length)
	{
		//找出每个单词出现次数并去除同样字符串
		
		int tnum=0,relength=length;
		Map<String, String> existMap = new HashMap<String, String>();	
		for(int i=0;i<length;i++)//将数据存入一个数组，有相同字符串ACCTIMES就+1
		{
			
			if(existMap.get(trnode[i].treenode)==null)//字符串不存在
			 {
				 existMap.put(trnode[i].treenode,Integer.toString(trnode[i].acctimes));
				 treenode[tnum].NodeCopy(trnode[i]);
					tnum++;
			 }
			else if(existMap.get(trnode[i].treenode)!=null)//字符串已存在
			{
				existMap.put(trnode[i].treenode,Integer.toString(trnode[i].acctimes+1));
				relength--;
			}
		}
		for(int i=0;i<length;i++)
		{//存入出现次数
			try
				{
				treenode[i].acctimes=Integer.valueOf(existMap.get(treenode[i].treenode)).intValue();
				}
			catch(Exception e){}
		}
		return length;
		 
	}
	private static void fiwrite(TreeNode trnode[],int dep,int length)
	{
		try
		{
			File file = new File("D://test_1.txt");	
			FileWriter fw_clear = new FileWriter(file);
			BufferedWriter bw_clear = new BufferedWriter(fw_clear);
			bw_clear.write("");
			bw_clear.close();
		}
		catch(Exception e){}
		try
		{
			File file = new File("D://test_1.txt");							
			FileWriter fw = new FileWriter(file,true);
			BufferedWriter bw = new BufferedWriter(fw);
			bw.write("深度为："+dep);