Ok, you asked for it:
File file = new File("myfile.txt");
// convert File to byte[]
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(bos);
oos.writeObject(file);
bos.close();
oos.close();
byte[] bytes = bos.toByteArray();
// convert byte[] to File
ByteArrayInputStream bis = new ByteArrayInputStream(bytes);
ObjectInputStream ois = new ObjectInputStream(bis);
File fileFromBytes = (File) ois.readObject();
bis.close();
ois.close();
System.out.println(fileFromBytes);
But this is pointless. Please specify what you are trying to achieve.