Iterator(迭代器)模式

最新推荐文章于 2024-11-04 09:35:00 发布

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最新推荐文章于 2024-11-04 09:35:00 发布

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分类专栏：程序设计与实现文章标签： iterator class null delete

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本文介绍了一种常用的设计模式——迭代器模式，并通过C++代码示例详细解释了其工作原理。迭代器模式允许顺序访问聚合对象中的元素，而无需暴露对象的内部结构。

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作用:
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.

在STL的实现中,所有的迭代器(Iterator)都遵照了这套规范。另外在多种遍历方法中，如前序，后序，中序以及广度优先遍历等，都可以用不同的迭代器类来支持。

typedef 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;
private:
};

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;
int m_nIndex;
};

#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;
}
DATA ConcreateAggregate::GetItem(int nIndex)
{
if (nIndex < m_nSize)
{
return m_pData[nIndex];
}
else
{
return -1;
}
}
ConcreateIterater::ConcreateIterater(Aggregate* pAggregate)
: m_pConcreateAggregate(pAggregate)
, m_nIndex(0)
{
}
void ConcreateIterater::First()
{
m_nIndex = 0;
}
void ConcreateIterater::Next()
{
if (m_nIndex < m_pConcreateAggregate->GetSize())
{
++m_nIndex;
}
}
bool ConcreateIterater::IsDone()
{
return m_nIndex == m_pConcreateAggregate->GetSize();
}
DATA ConcreateIterater::CurrentItem()
{
return m_pConcreateAggregate->GetItem(m_nIndex);
}

int main()
{
Aggregate* pAggregate = new ConcreateAggregate(4);
Iterater* pIterater = new ConcreateIterater(pAggregate);
for (; false == pIterater->IsDone(); pIterater->Next())
{
std::cout << pIterater->CurrentItem() << std::endl;
}
return 0;
}