我与C++设计模式（二十一）——迭代器模式

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迭代器模式，不用过多的介绍，迭代器在STL中是极具重要地位的。迭代器模式是用来解决对一个对象集合进行遍历的问题，将对集合的遍历封装成类，避免过多暴露。

UML图：

感觉比预想的要复杂。

代码：

#ifndef _AGGREGATE_H__#define _AGGREGATE_H__class Iterator;typedef int object;class aggregate{        public:                virtual ~aggregate();                virtual Iterator *create_Iterator() = 0;                virtual object get_item(int) = 0;                virtual int get_size() = 0;        protected:                aggregate();};class concrete_aggregate:public aggregate{        public:                enum{SIZE = 3};                concrete_aggregate();                ~concrete_aggregate();                Iterator *create_Iterator();                object get_item(int);                int get_size();        private:                object _obj[SIZE];};#endif

#ifndef _AGGREGATE_H__#define _AGGREGATE_H__class Iterator;typedef int object;class aggregate{        public:                virtual ~aggregate();                virtual Iterator *create_Iterator() = 0;                virtual object get_item(int) = 0;                virtual int get_size() = 0;        protected:                aggregate();};class concrete_aggregate:public aggregate{        public:                enum{SIZE = 3};                concrete_aggregate();                ~concrete_aggregate();                Iterator *create_Iterator();                object get_item(int);                int get_size();        private:                object _obj[SIZE];};#endifAdministrator@5guo-PC ~/pattern23/iterator$ cat aggregate.cpp//aggregate.cpp#include "aggregate.h"#include "iterator.h"aggregate::aggregate(){}aggregate::~aggregate(){}concrete_aggregate::concrete_aggregate(){        for (int i = 0; i < SIZE; ++i)                _obj[i] = i;}concrete_aggregate::~concrete_aggregate(){}Iterator *concrete_aggregate::create_Iterator(){        return new concrete_Iterator(this);}object concrete_aggregate::get_item(int index){        if (index < get_size())                return _obj[index];        else                return -1;}int concrete_aggregate::get_size(){        return SIZE;}

#ifndef _ITERATOR_H__#define _ITERATOR_H__class aggregate;typedef int object;class Iterator{        public:                virtual ~Iterator();                virtual void first() = 0;                virtual void next() = 0;                virtual bool is_done() = 0;                virtual object current_item() = 0;        protected:                Iterator();};class concrete_Iterator:public Iterator{        public:                concrete_Iterator(aggregate *,int index = 0);                ~concrete_Iterator();                void first();                void next();                bool is_done();                object current_item();        private:                aggregate *_p_ag;                int _idx;};#endif

//Iterator.cpp#include "aggregate.h"#include "Iterator.h"Iterator::Iterator(){}Iterator::~Iterator(){}concrete_Iterator::concrete_Iterator(aggregate *p_ag,int index)        :_p_ag(p_ag),_idx(index){}concrete_Iterator::~concrete_Iterator(){}object concrete_Iterator::current_item(){        return _p_ag->get_item(_idx);}void concrete_Iterator::first(){        _idx = 0;}void concrete_Iterator::next(){        if (_idx < _p_ag->get_size())                ++_idx;}bool concrete_Iterator::is_done(){        return _idx == _p_ag->get_size();}

//main.cpp#include "Iterator.h"#include "aggregate.h"#include <iostream>using namespace std;int main(int argc,char **argv){        aggregate *p_ag = new concrete_aggregate();        Iterator *p_ite = new concrete_Iterator(p_ag);        for ( ; !(p_ite->is_done()); p_ite->next())                cout<<p_ite->current_item()<<endl;        return 0;}

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