[设计形式]Iterator迭代器模式

[设计模式]Iterator迭代器模式
问题

iterator模式应该是最为熟悉的模式了，最简单的证明就是在实现Composite模式，Flyweight模式，Observer模式中就直接用到了STL提供的Iterator来遍历Vector或者List数据结构。

Iterator模式也正是用来解决对一个聚合对象的遍历问题，将对聚合的遍历封装到一个类中进行，这样就避免了暴露这个聚合对象的内部表示的可能。

提供一种方法顺序访问一个聚合对象中各个元素, 而又不需暴露该对象的内部表示。

iterator.h

#ifndef ITERATOR_H#define ITERATOR_Htypedef int DATA;class Iterater;// 容器的抽象基类class Aggregate{public:virtual ~Aggregate(){}virtual Iterater* CreateIterater(Aggregate *pAggregate) = 0;virtual int GetSize() = 0;virtual DATA GetItem(int nIndex) = 0;};// 迭代器的抽象基类class Iterater{public:virtual ~Iterater(){}virtual void First()= 0;virtual void Next()= 0;virtual bool IsDone()= 0;virtual DATA CurrentItem()= 0; };// 一个具体的容器类,这里是用数组表示class ConcreateAggregate: public Aggregate{public:ConcreateAggregate(int nSize);virtual ~ConcreateAggregate();virtual Iterater* CreateIterater(Aggregate *pAggregate);virtual int GetSize();virtual DATA GetItem(int nIndex);private:int m_nSize;DATA *m_pData;};// 访问ConcreateAggregate容器类的迭代器类class ConcreateIterater : public Iterater{public:ConcreateIterater(Aggregate* pAggregate);virtual ~ConcreateIterater(){}virtual void First();virtual void Next();virtual bool IsDone();virtual DATA CurrentItem();private:Aggregate  *m_pConcreateAggregate;intm_nIndex;};#endif

iterator.cpp

#include <iostream>#include "Iterator.h"ConcreateAggregate::ConcreateAggregate(int nSize) : m_nSize(nSize), m_pData(NULL){m_pData = new DATA[m_nSize];for (int i = 0; i < nSize; ++i){m_pData[i] = i;}}ConcreateAggregate::~ConcreateAggregate(){delete [] m_pData;m_pData = NULL;}Iterater* ConcreateAggregate::CreateIterater(Aggregate *pAggregate){return new ConcreateIterater(this);}int ConcreateAggregate::GetSize(){return m_nSize;}

main.cpp

#include "Iterator.h"#include <iostream>int main(){Aggregate* pAggregate = new ConcreateAggregate(4);Iterater*  pIterater  = new ConcreateIterater(pAggregate);for (; false == pIterater->IsDone(); pIterater->Next()){std::cout << pIterater->CurrentItem() << std::endl;}    system("pause");return 0;}