这个代码如何改就正确了

import java.io.*;public class ReadFileRW{    public static void main(String []args)    {        StringBuffer sb=new StringBuffer();        char ch;        try        {            while((ch=(char)System.in.read())!="\n")            {                sb.append(ch);            }            RandomAccessFile raf=new RandomAccessFile("D:\\HelloWorld\\User.txt","rw");            raf.seek(raf.length());            raf.writeBytes(sb.toString());            raf.close();        }catch(Exception e)        {            e.printStackTrace();        }    }}