1 信息隐藏的例子

class Door
{
public:
    enum State
    {
        closed = 1;
        opening,
        open,
        closing
    };
    //这里，枚举State需要在类外声明才能调用get函数，枚举的信息被暴露
    State getState() const
    {
        return m_state;
    }
private
    State m_state;
};

需要对get函数进行修改，同时使用枚举类防止被转换成其他类型：

class Door
{
public:
    //这回，类外只知道true or false
    bool isClosed() const;
    bool isClosing() const;
    bool isOpen() const;
    bool isOpening() const;
private
    enum class State //枚举类
    {
        closed = 1;
        opening,
        open,
        closing
    };
    State m_state;
};

2 高内聚的例子

3 低耦合的例子