IO流把int 改成character 然后文件就不断增长，从1K涨到了200多M

public static void demo_read() throws IOException{
FileInputStream fis=new FileInputStream("H://aa.txt");
BufferedInputStream bufis=new BufferedInputStream(fis);

    FileOutputStream fos=new FileOutputStream("J://copya.txt");
    BufferedOutputStream bufos=new BufferedOutputStream(fos);
    Character ch=0;
    while((ch=(char) bufis.read())!=-1){
        bufos.write(ch);

    }
    bufos.close();
    bufis.close();

}

谁能说说啊，这个问题百思不得其解