Iterator Pattern

1.Iterator模式用來解決對一個聚合對象的遍歷問題，將對聚合的遍歷封裝到一個類中進行，這樣就避免了暴露這個聚合對象的內部表示的可能.

2.Iterator 模式結構圖

3.實現

 1 #ifndef _AGGREGATE_H_ 
 2 #define _AGGREGATE_H_
 3 
 4 class Iterator;
 5 typedef int Object;
 6 class Interator;
 7 
 8 class Aggregate 
 9 { 
10 public: 
11     virtual ~Aggregate();
12     virtual Iterator* CreateIterator() = 0;
13     virtual Object GetItem(int idx) = 0;
14     virtual int GetSize() = 0;
15 
16 protected: 
17     Aggregate();
18 
19 private:
20 };
21 
22 class ConcreteAggregate:public Aggregate 
23 {
24 public: 
25     enum 
26     {
27         SIZE = 3
28     };    
29     ConcreteAggregate();
30     ~ConcreteAggregate();
31     Iterator* CreateIterator();
32     Object GetItem(int idx);
33     int GetSize();
34 
35 protected:
36 private: 
37     Object _objs[SIZE];
38 };
39 
40 #endif

Aggregate.h

 1 #include "Aggregate.h" 
 2 #include "Iterator.h"
 3 #include <iostream> 
 4 
 5 using namespace std;
 6 
 7 Aggregate::Aggregate() 
 8 {
 9 
10 }
11 Aggregate::~Aggregate() 
12 {
13 
14 }
15 ConcreteAggregate::ConcreteAggregate()
16 { 
17     for (int i = 0; i < SIZE; i++) 
18         _objs[i] = i; 
19 }
20 ConcreteAggregate::~ConcreteAggregate()
21 {
22 
23 }
24 Iterator* ConcreteAggregate::CreateIterator()
25 { 
26     return new ConcreteIterator(this);
27 }
28 Object ConcreteAggregate::GetItem(int idx) 
29 { 
30     if (idx < this->GetSize()) 
31         return _objs[idx];
32     else
33         return -1; 
34 }
35 int ConcreteAggregate::GetSize() 
36 { 
37     return SIZE; 
38 }

Aggregate.cpp

 1 #ifndef _ITERATOR_H_ 
 2 #define _ITERATOR_H_
 3 
 4 class Aggregate;
 5 typedef int Object;
 6 
 7 class Iterator 
 8 { 
 9 public: 
10     virtual ~Iterator();
11     virtual void First() = 0;
12     virtual void Next() = 0;
13     virtual bool IsDone() = 0;
14     virtual Object CurrentItem() = 0;
15 
16 protected: 
17     Iterator();
18 private:
19 };
20 
21 class ConcreteIterator:public Iterator
22 { 
23 public: 
24     ConcreteIterator(Aggregate* ag , int idx = 0);
25     ~ConcreteIterator();
26     void First();
27     void Next();
28     bool IsDone();
29     Object CurrentItem();
30 
31 protected:
32 private:
33     Aggregate* _ag;
34     int _idx;
35 };
36 
37 #endif

Iterator.h

 1 #include "Iterator.h" 
 2 #include "Aggregate.h" 
 3 #include <iostream> 
 4 using namespace std;
 5 
 6 Iterator::Iterator() 
 7 {
 8 
 9 }
10 Iterator::~Iterator() 
11 {
12 
13 }
14 ConcreteIterator::ConcreteIterator(Aggregate* ag , int idx)
15 { 
16     this->_ag = ag;
17     this->_idx = idx; 
18 }
19 ConcreteIterator::~ConcreteIterator() 
20 {
21 
22 }
23 Object ConcreteIterator::CurrentItem()
24 { 
25     return _ag->GetItem(_idx); 
26 }
27 void ConcreteIterator::First()
28 {
29     _idx = 0; 
30 }
31 void ConcreteIterator::Next() 
32 { 
33     if (_idx < _ag->GetSize()) 
34         _idx++;
35 }
36 bool ConcreteIterator::IsDone() 
37 { 
38     return (_idx == _ag->GetSize());
39 }

Iterator

 1 #include "Iterator.h" 
 2 #include "Aggregate.h"
 3 #include <iostream> 
 4 using namespace std;
 5 
 6 int main(int argc,char* argv[]) 
 7 {
 8     Aggregate* ag = new ConcreteAggregate();
 9     Iterator* it = new ConcreteIterator(ag);
10     for (; !(it->IsDone()) ; it->Next()) 
11     { 
12         cout<<it->CurrentItem()<<endl; 
13     }
14 
15     return 0; 
16 }

main.cpp