当输入流和输出流同时作用一个文件

import java.io.*;
class Demo{
    public static void main(String[] args)throws IOException{
        File file=new File("C:\\Demo.txt");//这个文件只有一行
        BufferedReader br=new BufferedReader(new FileReader(file));
        BufferedWriter bw=new BufferedWriter(new FileWriter(file,file.isFile()));
        System.out.println(br.readLine());
        bw.newLine();
        bw.write("我写啦");
        bw.flush();
        System.out.println(br.readLine());

        }
}