我个人的感觉：通过练习数据结构在不同语言中的实现，可以很快熟悉新学语言，了解彼此的差异。

    Java类中的嵌套类可以就是类中的一个field，可以在嵌套类中直接访问其它field，而嵌套类中的field也对外面暴露！而在C#中情况却与JAVA不同，其又没有C++的friend关键字！怎么办？我在网上看到一个网站号称《 Data Structures and Algorithms with Object-Oriented Design Patterns 》，起上有C++、JAVA、C#数据结构实现的源码，看看别人的定义：
以LinkedList为例：
//
//   This file contains the C++ code from Program 4.9 of
//   "Data Structures and Algorithms
//    with Object-Oriented Design Patterns in C++"
//   by Bruno R. Preiss.
//
//   Copyright (c) 1998 by Bruno R. Preiss, P.Eng.  All rights reserved.
//
//   http://www.pads.uwaterloo.ca/Bruno.Preiss/books/opus4/programs/pgm04_09.cpp
//
template <class T>//此处如不事先声明，C++编译器会提示（*）中找不到LinkedList
class LinkedList;//而C#不必如此！

template <class T>
class ListElement
{
    T datum;
    ListElement* next;

    ListElement (T const&, ListElement*);
public:
    T const& Datum () const;
    ListElement const* Next () const;

    friend LinkedList<T>;//*
};

template <class T>
class LinkedList
{
    ListElement<T>* head;
    ListElement<T>* tail;
public:
    LinkedList ();
    ~LinkedList ();

    LinkedList (LinkedList const&);
    LinkedList& operator = (LinkedList const&);

    ListElement<T> const* Head () const;
    ListElement<T> const* Tail () const;
    bool IsEmpty () const;
    T const& First () const;
    T const& Last () const;

    void Prepend (T const&);
    void Append (T const&);
    void Extract (T const&);
    void Purge ();
    void InsertAfter (ListElement<T> const*, T const&);
    void InsertBefore (ListElement<T> const*, T const&);
};

//
//   This file contains the Java code from Program 4.13 of
//   "Data Structures and Algorithms
//    with Object-Oriented Design Patterns in Java"
//   by Bruno R. Preiss.
//
//   Copyright (c) 1998 by Bruno R. Preiss, P.Eng.  All rights reserved.
//
//   http://www.pads.uwaterloo.ca/Bruno.Preiss/books/opus5/programs/pgm04_13.txt
//
public class LinkedList
{
    protected Element head;
    protected Element tail;

    public final class Element//嵌套类，使用private修饰应该也可以
    {
 Object datum;
 Element next;

 Element (Object datum, Element next)
 {
     this.datum = datum;
     this.next = next;
 }

 public Object getDatum ()
     { return datum; }

 public Element getNext ()
     { return next; }
 // ...
    }
    // ...
}

//
//   This file contains the C# code from Program 4.12 of
//   "Data Structures and Algorithms
//    with Object-Oriented Design Patterns in C#"
//   by Bruno R. Preiss.
//
//   Copyright (c) 2001 by Bruno R. Preiss, P.Eng.  All rights reserved.
//     注意：C#的历史也有几年了！哈哈！
//   http://www.pads.uwaterloo.ca/Bruno.Preiss/books/opus6/programs/pgm04_12.txt
//
public class LinkedList
{
    protected Element head;
    protected Element tail;

    public sealed class Element//关键字sealed与Java的final类似，但是final功能多！
    {
 internal LinkedList list;//关键字internal
 internal object datum;
 internal Element next;

 internal Element(
     LinkedList list, object datum, Element next)
 {
     this.list = list;
     this.datum = datum;
     this.next = next;
 }

 public object Datum
     { get { return datum; } }

 public Element Next
     { get { return next; } }
 // ...
    }
    // ...
}

URL：http://www.brpreiss.com/
其网站上有在线文档，还有各个类与接口间的关系图。把它们都领会还是要费些功夫，我正在努力中！
我想在这里我们还可以学到如何组织类、接口，个语言间的异同。在学习数据结构时还可以接触Pattern的思想，何乐而不为！
如果你熟悉数据结构可以直接下载源代码来看，且当复习！