// Gravar
    try {
            FileOutputStream f_out = new FileOutputStream("NOME_DO_ARQUIVO");
            ObjectOutputStream o_out = new ObjectOutputStream(f_out);
            
            o_out.writeObject(ObjectQueEuQueroGravar);
            o_out.close();
            f_out.close();
    }

// Ler

 try {
            FileInputStream f_in = new FileInputStream("NOME_DO_ARQUIVO");
            ObjectInputStream o_in = new ObjectInputStream(f_in);
            objeto_para_ler = (ClasseDoObjeto) o_in.readObject();
            f_in.close();
            o_in.close();
        }