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<HTML><BODY BGCOLOR = #FFFFFF><H1>Foundation Classes</H1><A NAME="chapter_foundation"></A><P>This appendix documents the foundation classes we use in the C++sample code of several design patterns. We've intentionally kept theclasses simple and minimal. We describe the following classes:</P><UL><LI><CODE>List</CODE>, an ordered list of objects.</LI><LI><CODE>Iterator</CODE>,the interface for accessing an aggregate's objects in a sequence.</LI><LI><CODE>ListIterator</CODE>,an iterator for traversing a <CODE>List</CODE>.</LI><LI><CODE>Point</CODE>, a two-dimensional point.</LI><LI><CODE>Rect</CODE>, an axis-aligned rectangle.</LI></UL><P>Some newer C++ standard types may not be available on allcompilers. In particular, if your compiler doesn't define<CODE>bool</CODE>, then define it manually as</P><PRE>typedef int bool;const int true = 1;const int false = 0;</PRE><H2>List</H2><P>The <CODE>List</CODE> class template provides a basic container forstoring an ordered list of objects. <CODE>List</CODE> stores elements byvalue, which means it works for built-in types as well as classinstances. For example, <CODE>List<int></CODE> declares a list of<CODE>int</CODE>s. But most of the patterns use <CODE>List</CODE> tostore pointers to objects, as in <CODE>List<Glyph*></CODE>. That way<CODE>List</CODE> can be used for heterogeneous lists.</P><P>For convenience, <CODE>List</CODE> also provides synonyms for stackoperations, which make code that uses <CODE>List</CODE> for stacks moreexplicit without defining another class.</P><PRE>template <class Item>class List {public: List(long size = DEFAULT_LIST_CAPACITY); List(List&); List(); List& operator=(const List&); long Count() const; Item& Get(long index) const; Item& First() const; Item& Last() const; bool Includes(const Item&) const; void Append(const Item&); void Prepend(const Item&); void Remove(const Item&); void RemoveLast(); void RemoveFirst(); void RemoveAll(); Item& Top() const; void Push(const Item&); Item& Pop();};</PRE><P>The following sections describe these operations in greater detail.</P><H3>Construction, Destruction, Initialization, and Assignment</H3><DL><DT><CODE>List(long size)</CODE></DT><DD>initializes the list. The <CODE>size</CODE> parameter is a hint forthe initial number of elements.</DD><DT><CODE>List(List&)</CODE></DT><DD>overrides the default copy constructor so that member data areinitialized properly.</DD><DT><CODE>~List()</CODE></DT><DD>frees the list's internal data structures but <EM>not</EM> theelements in the list. The class is not designed for subclassing;therefore the destructor isn't virtual.</DD><DT><CODE>List& operator=(const List&)</CODE></DT><DD>implements the assignment operation to assign member data properly.</DD></DL><H3>Accessing</H3><P>These operations provide basic access to the list's elements.<DL><DT><CODE>long Count() const</CODE></DT><DD>returns the number of objects in the list.</DD><DT><CODE>Item& Get(long index) const</CODE></DT><DD>returns the object at the given index.</DD><DT><CODE>Item& First() const</CODE></DT><DD>returns the first object in the list.</DD><DT><CODE>Item& Last() const</CODE></DT><DD>returns the last object in the list.</DD></DL><H3>Adding</H3><DL><DT><CODE>void Append(const Item&)</CODE></DT><DD>adds the argument to the list, making it the last element.</DD><DT><CODE>void Prepend(const Item&)</CODE></DT><DD>adds the argument to the list, making it the first element.</DD></DL><H3>Removing</H3><DL><DT><CODE>void Remove(const Item&)</CODE></DT><DD>removes the given element from the list. This operation requiresthat the type of elements in the list supports the<CODE>==</CODE> operator for comparison.</DD><DT><CODE>void RemoveFirst()</CODE></DT><DD>removes the first element from the list.</DD><DT><CODE>void RemoveLast()</CODE></DT><DD>removes the last element from the list.</DD><DT><CODE>void RemoveAll()</CODE></DT><DD>removes all elements from the list.</DD></DL><H3>Stack Interface</H3><DL><DT><CODE>Item& Top() const</CODE></DT><DD>returns the top element (when the List is viewed as a stack).</DD><DT><CODE>void Push(const Item&)</CODE></DT><DD>pushes the element onto the stack.</DD><DT><CODE>Item& Pop()</CODE></DT><DD>pops the top element from the stack.</DD></DL><H2>Iterator</H2><P><CODE>Iterator</CODE> is an abstract class that defines a traversalinterface for aggregates.</P><PRE>template <class Item>class Iterator {public: virtual void First() = 0; virtual void Next() = 0; virtual bool IsDone() const = 0; virtual Item CurrentItem() const = 0;protected: Iterator();};</PRE><P>The operations do the following:</P><DL><DT><CODE>virtual void First()</CODE></DT><DD>positions the iterator to the first object in the aggregate.</DD><DT><CODE>virtual void Next()</CODE></DT><DD>positions the iterator to the next object in the sequence.</DD><DT><CODE>virtual bool IsDone() const</CODE></DT><DD>returns <CODE>true</CODE> when there are no more objects in the sequence.</DD><DT><CODE>virtual Item CurrentItem() const</CODE></DT><DD>returns the object at the current position in the sequence.</DD></DL><H2>ListIterator</H2><P><CODE>ListIterator</CODE> implements the <CODE>Iterator</CODE> interfaceto traverse List objects. Its constructor takes a list to traverse asan argument.</P><PRE>template <class Item>class ListIterator : public Iterator<Item> {public: ListIterator(const List<Item>* aList); virtual void First(); virtual void Next(); virtual bool IsDone() const; virtual Item CurrentItem() const;};</PRE><H2>Point</H2><P><CODE>Point</CODE> represents a point in a two-dimensional Cartesiancoordinate space. <CODE>Point</CODE> supports some minimal vector arithmetic.The coordinates of a <CODE>Point</CODE> are defined as</P><PRE>typedef float Coord;</PRE><P><CODE>Point</CODE>'s operations are self-explanatory.</P><PRE>class Point {public: static const Point Zero; Point(Coord x = 0.0, Coord y = 0.0); Coord X() const; void X(Coord x); Coord Y() const; void Y(Coord y); friend Point operator+(const Point&, const Point&); friend Point operator-(const Point&, const Point&); friend Point operator*(const Point&, const Point&); friend Point operator/(const Point&, const Point&); Point& operator+=(const Point&); Point& operator-=(const Point&); Point& operator*=(const Point&); Point& operator/=(const Point&); Point operator-(); friend bool operator==(const Point&, const Point&); friend bool operator!=(const Point&, const Point&); friend ostream& operator<<(ostream&, const Point&); friend istream& operator>>(istream&, Point&);};</PRE><P>The static member <CODE>Zero</CODE> represents <CODE>Point(0, 0)</CODE>.<H2>Rect</H2><P><CODE>Rect</CODE> represents an axis-aligned rectangle. A<CODE>Rect</CODE> is defined by an origin point and an extent (thatis, width and height). The <CODE>Rect</CODE> operations areself-explanatory.</P><PRE>class Rect {public: static const Rect Zero; Rect(Coord x, Coord y, Coord w, Coord h); Rect(const Point& origin, const Point& extent); Coord Width() const; void Width(Coord); Coord Height() const; void Height(Coord); Coord Left() const; void Left(Coord); Coord Bottom() const; void Bottom(Coord); Point& Origin() const; void Origin(const Point&); Point& Extent() const; void Extent(const Point&); void MoveTo(const Point&); void MoveBy(const Point&); bool IsEmpty() const; bool Contains(const Point&) const;};</PRE><P>The static member <CODE>Zero</CODE> is equivalent to the rectangle</P><PRE>Rect(Point(0, 0), Point(0, 0));</PRE></BODY></HTML>⌨️ 快捷键说明
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