вопрос по FileOutputStream

Solution sol=new Solution("O://1.txt");

public class Solution implements Serializable, AutoCloseable {
    private transient FileOutputStream stream;
    private String fileName;

    public Solution(String fileName) throws FileNotFoundException {
        this.fileName = fileName;
        this.stream = new FileOutputStream(fileName);
    }

    public void writeObject(String string) throws IOException {
        stream.write(string.getBytes());
        stream.write("\n".getBytes());
        stream.flush();
    }

    private void writeObject(ObjectOutputStream out) throws IOException {
        out.defaultWriteObject();
    }

    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
        in.defaultReadObject();
        this.stream=new FileOutputStream(fileName, true);
    }

    @Override
    public void close() throws Exception {
        System.out.println("Closing everything!");
        stream.close();
    }

    public static void main(String[] args) throws IOException, ClassNotFoundException {
        Solution sol=new Solution("O://1.txt");
        sol.writeObject("MyString");
        ByteArrayOutputStream aOut=new ByteArrayOutputStream();
        ObjectOutputStream oOut=new ObjectOutputStream(aOut);
        oOut.writeObject(sol);
        ByteArrayInputStream aIn=new ByteArrayInputStream(aOut.toByteArray());
        ObjectInputStream oIn=new ObjectInputStream(aIn);
        Solution sol2=(Solution) oIn.readObject();
        sol2.writeObject("MoreString");
    }
}