行为型模式-迭代器(iterator)

迭代器

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.

实例

main.cc:

#include <windows.h>#include "runner_club.h"#include "runner_iterator.h"#include <iostream>using namespace std;/*design_pattern:"iterator"list all members of the runner club.*/int main(){    RunnerClub *runner_club = new RunnerClub();    runner_club->Append("zhang san");    runner_club->Append("li si");    runner_club->Append("wang wu");    Iterator *iterator = runner_club->CreateIterator();    for(;!iterator->IsEnd();iterator->Next()){        cout << iterator->GetCurrent() << endl;    }    //clear    delete runner_club;    system("Pause");    return 0;}

Club:

//club.h#ifndef HELENDP_SOURCE_CLUB_H_#define HELENDP_SOURCE_CLUB_H_#include "iterator.h"#include <string>using namespace std;class Club{public:    Club();    virtual ~Club();    virtual int GetTotal() = 0;    virtual void Append(string name) = 0;    virtual string Gain(int index) = 0;     virtual Iterator* CreateIterator() = 0;};#endif//club.cc#include "club.h"Club::Club(){}Club::~Club(){}

RunnerClub:

//runner_club.h#ifndef HELENDP_SOURCE_RUNNER_CLUB_H_#define HELENDP_SOURCE_RUNNER_CLUB_H_#include "club.h"#include <vector>using namespace std;class RunnerClub : public Club{public:    RunnerClub();    ~RunnerClub();    int GetTotal();    void Append(string name);    string Gain(int index);     Iterator* CreateIterator();private:    Iterator *iterator_;    vector<string> vector_;};#endif//runner_club.cc#include "runner_club.h"#include "runner_iterator.h"#include <stdio.h>#include <iostream>using namespace std;RunnerClub::RunnerClub(){    iterator_ = NULL;    vector_.clear();}RunnerClub::~RunnerClub(){    if(!iterator_){        delete iterator_;        iterator_ = NULL;    }}int RunnerClub::GetTotal(){    return vector_.size();}void RunnerClub::Append(string name){    vector_.push_back(name);}string RunnerClub::Gain(int index){    return vector_[index % vector_.size()];}Iterator* RunnerClub::CreateIterator(){    iterator_ = new RunnerIterator(this);    return iterator_;}

Iterator:

//iterator.h#ifndef HELENDP_SOURCE_ITERATOR_H_#define HELENDP_SOURCE_ITERATOR_H_#include <string>using namespace std;class Iterator{public:    Iterator();    virtual ~Iterator();    virtual string First() = 0;    virtual string Next() = 0;    virtual bool IsEnd() = 0;    virtual string GetCurrent() = 0;};#endif//iterator.cc#include "iterator.h"Iterator::Iterator(){}Iterator::~Iterator(){}

RunnerIterator:

//runner_iterator.h#ifndef HELENDP_SOURCE_RUNNER_ITERATOR_H_#define HELENDP_SOURCE_RUNNER_ITERATOR_H_#include "iterator.h"#include "club.h"class RunnerIterator : public Iterator{public:    RunnerIterator(Club* club);    ~RunnerIterator();    string First();    string Next();    bool IsEnd();    string GetCurrent();    private:    int index_;    Club *club_;};#endif//runner_iterator.cc#include "runner_iterator.h"RunnerIterator::RunnerIterator(Club* club)    :index_(0){    club_ = club;}RunnerIterator::~RunnerIterator(){}string RunnerIterator::First(){    return club_->Gain(0);}string RunnerIterator::Next(){    index_ %= club_->GetTotal();    return club_->Gain(index_++);}string RunnerIterator::GetCurrent(){    return club_->Gain(index_);}bool RunnerIterator::IsEnd(){    return (index_ >= club_->GetTotal() ? true : false );}

代码和UML图(EA)工程文件,最后会整理打包上传.

UML类图

结构

• Iterator(Iterator):迭代器定义访问和遍历元素的接口.
• ConcreteIterator(RunnerIterator):实现迭代器的类.
• Aggregate(Club):创建相应迭代器的接口.
• ConcreteAggregate(RunnerClub):实现相应迭代器类.

优点

• 访问一个聚合对象的内容而无需暴露它的内部表示.
• 简化了聚合的接口.
• 在同一个聚合上可以有多个遍历.

缺点

• 对于比较简单的遍历数据聚合，使用迭代器方式遍历较为繁琐.