ObjectOutputStream does not write objects when taking BufferedOutputStream

I've done my research but it seems I can't find enough documentation on the subject.

When trying out some code on Object streams, I came to notice that putting a BufferedOutputStream inside an ObjectOutputStream causes the file to be ill-written. Just to makes things clearer here's the code I've used:

public class Objectstream implements Serializable{

private static final long serialVersionUID = 1L;
public int x;

public Objectstream(){}
public Objectstream(int x){
    this.x = x;
}

public static void main(String[] args) {

    try(
            //ObjectOutputStream objOutStream = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream("/homes/f17oudbi/Bureau/o.txt")));//1
            ObjectOutputStream objOutStream = new ObjectOutputStream(new FileOutputStream("o.txt"));//2
            ObjectInputStream objInputStream = new ObjectInputStream(new FileInputStream("o.txt"));

            ){

        Objectstream obj = new Objectstream(7);

        objOutStream.writeObject(obj);
        objOutStream.flush();

        System.out.println(((Objectstream)objInputStream.readObject()).x);


    }catch(EOFException e){
        e.printStackTrace();
    }
    catch(Exception e){
        e.printStackTrace();
    }
}

}

If I decomment the first line and comment the second, the written Objectstream just writes \AC\ED\00\00 in the file (and that's independant of how I change it); But if I keep the code as is, it writes something with the reference on the object and does the job well.

Does anyone have an explanation why is this the case?

Edit:

I get the following exception java.io.EOFException pointing to the line where the ObjectOutputStream method is created.