Iterative sub-patterns of design patterns

Iterative sub-patterns of design patterns

The iterative sub-pattern, also called the cursor pattern, is the behavior pattern of the object. Iterative sub-patterns can sequentially access an element in a cluster without exposing the aggregated interior representation-Dr. Shanhong's Java and patterns

Example: Traversal of a collection first version: Implementing array collections and linked list collections

Collection interface

 Public Interface mycollection {    void  Add (Object o);     int size ();}

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Array Collection

 Public classmyArrayListImplementsmycollection {PrivateObject[] Objects =NewOBJECT[10];//Initial Container size    Private intPosition = 0;//cursor (the position of the next insertion element)@Override Public voidAdd (Object o) {if(Position = = Objects.length) {//if the container is full, expand the containerobject[] Newobjects =NewObject[objects.length * 2]; System.arraycopy (Objects,0, newobjects, 0, objects.length); Objects=newobjects; } Objects[position]=o; Position++; } @Override Public intsize () {returnposition; }}

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Linked List Collection

 Public classMylinkedlistImplementsmycollection {PrivateNode head =NULL; PrivateNode tail =NULL; Private intSize = 0; @Override Public voidAdd (Object o) {node node=NewNode (O,NULL); if(Head = =NULL) {//first oneHead =node; Tail=node; } Else{tail.setnext (node); Tail=node; } size++; } @Override Public intsize () {returnsize; }        classNode {PrivateObject data; PrivateNode Next;  Publicnode (Object data, node next) { This. data =data;  This. Next =Next; }         PublicObject GetData () {returndata; }         Public voidsetData (Object data) { This. data =data; }         PublicNode GetNext () {returnNext; }         Public voidSetnext (Node next) { This. Next =Next; }    }}

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OK, we found that myarraylist and Mylinkedlist have implemented the MyCollection interface, but the implementation method is different, resulting in a different way of traversal, in order to unify the way can only use an abstract class/interface Way

Second Edition: Unified Traversal method

Adding a unified traversal interface

 Public Interface myiterator {    Object next ();     Boolean hasnext ();}

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Let all the collection classes implement the interface (as long as the collection class that implements the MyCollection interface we can call its iterator () method to traverse its elements)

 Public Interface mycollection {    void  Add (Object o);     int size ();    Myiterator iterator ();}

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It's easy to go through the collection at this point.

 while (Iterator.hasnex ()) {    = iterator.next ();}

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Start implementing Myiterator-Array collection below

 Public classmyArrayListImplementsmycollection {PrivateObject[] Objects =NewOBJECT[10];//Initial Container size    Private intPosition = 0;//cursor (the position of the next insertion element)@Override Public voidAdd (Object o) {if(Position = = Objects.length) {//if the container is full, expand the containerobject[] Newobjects =NewObject[objects.length * 2]; System.arraycopy (Objects,0, newobjects, 0, objects.length); Objects=newobjects; } Objects[position]=o; Position++; } @Override Public intsize () {returnposition; } @Override PublicMyiterator iterator () {return NewMyiterator () {intindex = 0; @Override PublicObject Next () {returnObjects[index + +]; } @Override Public BooleanHasnext () {//if (Index < objects.length)//low-level error                if(Index <position)return true; return false;    }        }; }}

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Linked List Collection

 Public classMylinkedlistImplementsmycollection {PrivateNode head =NULL; PrivateNode tail =NULL; Private intSize = 0; @Override Public voidAdd (Object o) {node node=NewNode (O,NULL); if(Head = =NULL) {//first oneHead =node; Tail=node; } Else{tail.setnext (node); Tail=node; } size++; } @Override Public intsize () {returnsize; }        classNode {PrivateObject data; PrivateNode Next;  Publicnode (Object data, node next) { This. data =data;  This. Next =Next; }         PublicObject GetData () {returndata; }         Public voidsetData (Object data) { This. data =data; }         PublicNode GetNext () {returnNext; }         Public voidSetnext (Node next) { This. Next =Next; }} @Override PublicMyiterator iterator () {return NewMyiterator () {Node Currnode=Head; @Override Publicobject Next () {object o=Currnode.getdata (); Currnode=Currnode.getnext (); returno; } @Override Public BooleanHasnext () {returnCurrnode! =NULL;    }        }; }}

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Test

 Public classTest { Public Static voidMain (string[] args) {mycollection Al=Newmyarraylist (); mycollection ll=Newmylinkedlist ();  for(inti=0; i<15; i++) {al.add (i);        Ll.add (i); } Myiterator iterator= Ll.iterator ();//= Al.iterator ();         while(Iterator.hasnext ()) {System.out.print (Iterator.next () )+ " "); }    }}

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Ok, the above is the Cottage Beggar version jdk ArrayList and LinkedList

Iterative sub-patterns of design patterns