请问二叉树等数据结构的物理存储结构是怎样的？

            public
            class
             BinTreeDiskSample {
    
            private
            static
            int Sn = -1;
    privatestatic Node root;
    staticprivateclass Node implements Serializable {
        privatestaticfinallong serialVersionUID = -4780741633734920991L;
        int data;
        transient Node left;
        transient Node right;
        int lHeight = -1, rHeight = -1;
        public Node(int data) {
            this.data = data;
        }
        public Node setLeft(Node left) {
            this.left = left;
            returnthis;
        }
        public Node setRight(Node right) {
            this.right = right;
            returnthis;
        }
        public Node getLeft() {
            return left;
        }
        public Node getRight() {
            return right;
        }
        // 后续遍历写入，先序遍历读出publicint write(ObjectOutputStream out) throws IOException {
            if (left != null) {
                lHeight = left.write(out);
            }
            if (right != null) {
                rHeight = right.write(out);
            }
            Sn++;
            out.writeObject(this);
            return Sn;
        }
        privatevoid init(List<Node> list) {
            if (lHeight != -1) {
                left = list.get(lHeight);
                left.init(list);
            }
            if (rHeight != -1) {
                right = list.get(rHeight);
                right.init(list);
            }
        }

    }
    publicstaticvoid binTreePreOrderPrint(Node root) {
        System.out.print(root.data + " ");      // visit rootif(root.left != null) {
            binTreePreOrderPrint(root.left);
        }
        if(root.right != null) {
            binTreePreOrderPrint(root.right);
        }
    }
    // 先序遍历读出publicstaticvoid read(ObjectInputStream in) throws IOException,
            ClassNotFoundException {
        List<Node> list = new ArrayList<Node>();
        Node n;
        Object obj;
        try {
            while ((obj = in.readObject()) != null) {
                n = (Node) obj;
                list.add(n);
            }
        }
        catch (Exception e) {
            // EOFException ...
//            e.printStackTrace();        }
        root = list.get(list.size() - 1);
        root.init(list);
    }
    publicstaticvoid main(String args[]) throws FileNotFoundException,
            IOException, ClassNotFoundException {
        // 构造一棵二叉树/*
         * 1 2 3 4 5 6
         */
        Node n6 = new Node(61);
        Node n4 = new Node(41).setLeft(n6);
        Node n5 = new Node(51);
        Node n2 = new Node(21).setLeft(n4).setRight(n5);
        Node n3 = new Node(31);
        Node n1 = new Node(11).setLeft(n2).setRight(n3);
        root = n1;
        System.out.println("output node: ");
        binTreePreOrderPrint(root);
        // 将数据写稿磁盘
        ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("btree.bin"));
        root.write(out);
        out.close();

        root = null;
        // 将数据从磁盘读入，并进行数据结构的重新构建
        ObjectInputStream in = new ObjectInputStream(new FileInputStream("btree.bin"));
        read(in);
        in.close();
        System.out.println("\nread node: ");
        binTreePreOrderPrint(root);
    }

}