| 名稱 |
Composite
|
| 結構 |
|
| 意圖 |
將對象組合成樹形結構以表示“部分-整體”的層次結構。C o m p o s i t e 使得用戶對單個對象和組合對象的使用具有一致性。 |
| 適用性 |
- 你想表示對象的部分-整體層次結構。
- 你希望用戶忽略組合對象與單個對象的不同，用戶將統一地使用組合結構中的所有對象。
|
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Code Example
namespace?FactoryMethod_DesignPattern
{
????using?System;
????using?System.Collections;
????abstract?class?Component?
????{
????????protected?string?strName;
????????public?Component(string?name)
????????{
????????????strName?=?name;
????????}
????????abstract?public?void?Add(Component?c);
????
????????public?abstract?void?DumpContents();
????????
????????//?other?operations?for?delete,?get,?etc.
????}
????class?Composite?:?Component
????{
????????private?ArrayList?ComponentList?=?new?ArrayList();
????????
????????public?Composite(string?s)?:?base(s)?{}
????????override?public?void?Add(Component?c)
????????{
????????????ComponentList.Add(c);
????????}
????????public?override?void?DumpContents()
????????{
????????????//?First?dump?the?name?of?this?composite?node
????????????Console.WriteLine("Node:?{0}",?strName);
????????????//?Then?loop?through?children,?and?get?then?to?dump?their?contents
????????????foreach?(Component?c?in?ComponentList)
????????????{
????????????????c.DumpContents();
????????????}
????????}
????}
????class?Leaf?:?Component
????{
????????public?Leaf(string?s)?:?base(s)?{}
????????override?public?void?Add(Component?c)
????????{
????????????Console.WriteLine("Cannot?add?to?a?leaf");
????????}
????????public?override?void?DumpContents()
????????{
????????????Console.WriteLine("Node:?{0}",?strName);
????????}
????}
????/**////?<summary>
????///????Summary?description?for?Client.
????///?</summary>
????public?class?Client
????{
????????Component?SetupTree()
????????{
????????????//?here?we?have?to?create?a?tree?structure,?
????????????//?consisting?of?composites?and?leafs.?????
????????????Composite?root?=?new?Composite("root-composite");
????????????Composite?parentcomposite;
????????????Composite?composite;
????????????Leaf?leaf;
????????????parentcomposite?=?root;
????????????composite?=?new?Composite("first?level?-?first?sibling?-?composite");
????????????parentcomposite.Add(composite);
????????????leaf?=?new?Leaf("first?level?-?second?sibling?-?leaf");
????????????parentcomposite.Add(leaf);
????????????parentcomposite?=?composite;?
????????????composite?=?new?Composite("second?level?-?first?sibling?-?composite");
????????????parentcomposite.Add(composite);
????????????composite?=?new?Composite("second?level?-?second?sibling?-?composite");
????????????parentcomposite.Add(composite);
????????????//?we?will?leaf?the?second?level?-?first?sibling?empty,?and?start?
????????????//?populating?the?second?level?-?second?sibling?
????????????parentcomposite?=?composite;?
????????????leaf?=?new?Leaf("third?level?-?first?sibling?-?leaf");
????????????parentcomposite.Add(leaf);
????????????
????????????leaf?=?new?Leaf("third?level?-?second?sibling?-?leaf");
????????????parentcomposite.Add(leaf);
????????????composite?=?new?Composite("third?level?-?third?sibling?-?composite");
????????????parentcomposite.Add(composite);
????????????return?root;
????????}
????????public?static?int?Main(string[]?args)
????????{???
???????????????Component?component;
????????????Client?c?=?new?Client();
????????????component?=?c.SetupTree();
????????????component.DumpContents();
????????????return?0;
????????}
????}
}
可以看出，Composite類型的對象可以包含其它Component類型的對象。換而言之，Composite類型對象可以含有其它的樹枝（Composite）類型或樹葉（Leaf）類型的對象。
合成模式的實現根據所實現接口的區別分為兩種形式，分別稱為安全模式和透明模式。合成模式可以不提供父對象的管理方法，但合成模式必須在合適的地方提供子對象的管理方法（諸如：add、remove、getChild等）。
透明方式
作為第一種選擇，在Component里面聲明所有的用來管理子類對象的方法，包括add（）、remove（），以及getChild（）方法。這樣做的好處是所有的構件類都有相同的接口。在客戶端看來，樹葉類對象與合成類對象的區別起碼在接口層次上消失了，客戶端可以同等同的對待所有的對象。這就是透明形式的合成模式。
這個選擇的缺點是不夠安全，因為樹葉類對象和合成類對象在本質上是有區別的。樹葉類對象不可能有下一個層次的對象，因此add（）、remove（）以及getChild（）方法沒有意義，是在編譯時期不會出錯，而只會在運行時期才會出錯。
安全方式
第二種選擇是在Composite類里面聲明所有的用來管理子類對象的方法。這樣的做法是安全的做法，因為樹葉類型的對象根本就沒有管理子類對象的方法，因此，如果客戶端對樹葉類對象使用這些方法時，程序會在編譯時期出錯。
這個選擇的缺點是不夠透明，因為樹葉類和合成類將具有不同的接口。
這兩個形式各有優缺點，需要根據軟件的具體情況做出取舍決定。
安全式的合成模式實現: 只有composite有Add ,remove,delete等方法.
以下示例性代碼演示了安全式的合成模式代碼：
//?Composite?pattern?--?Structural?example??
using?System;
using?System.Text;
using?System.Collections;
//?"Component"
abstract?class?Component
{
??//?Fields
??protected?string?name;
??//?Constructors
??public?Component(?string?name?)
??{
????this.name?=?name;
??}
??//?Operation
??public?abstract?void?Display(?int?depth?);
}
//?"Composite"
class?Composite?:?Component
{
??//?Fields
??private?ArrayList?children?=?new?ArrayList();
??//?Constructors
??public?Composite(?string?name?)?:?base(?name?)?{}
??//?Methods
??public?void?Add(?Component?component?)
??{
????children.Add(?component?);
??}
??public?void?Remove(?Component?component?)
??{
????children.Remove(?component?);
??}
??public?override?void?Display(?int?depth?)
??{
????Console.WriteLine(?new?String(?'-',?depth?)?+?name?);
????//?Display?each?of?the?node's?children
????foreach(?Component?component?in?children?)
??????component.Display(?depth?+?2?);
??}
}
//?"Leaf"
class?Leaf?:?Component
{
??//?Constructors
??public?Leaf(?string?name?)?:?base(?name?)?{}
??//?Methods
??public?override?void?Display(?int?depth?)
??{
????Console.WriteLine(?new?String(?'-',?depth?)?+?name?);
??}
}
/**////?<summary>
///?Client?test
///?</summary>public?class?Client
{
??public?static?void?Main(?string[]?args?)
??{
????//?Create?a?tree?structure
????Composite?root?=?new?Composite(?"root"?);
????root.Add(?new?Leaf(?"Leaf?A"?));
????root.Add(?new?Leaf(?"Leaf?B"?));
????Composite?comp?=?new?Composite(?"Composite?X"?);
????comp.Add(?new?Leaf(?"Leaf?XA"?)?);
????comp.Add(?new?Leaf(?"Leaf?XB"?)?);
????root.Add(?comp?);
????root.Add(?new?Leaf(?"Leaf?C"?));
????//?Add?and?remove?a?leaf
????Leaf?l?=?new?Leaf(?"Leaf?D"?);
????root.Add(?l?);
????root.Remove(?l?);
????//?Recursively?display?nodes
????root.Display(?1?);
??}
}?
透明式的合成模式實現: 每個里都有add,remove等修改方法.以下示例性代碼演示了安全式的合成模式代碼：
//?Composite?pattern?--?Structural?example??
using?System;
using?System.Text;
using?System.Collections;
//?"Component"
abstract?class?Component
{
??//?Fields
??protected?string?name;
??//?Constructors
??public?Component(?string?name?)
??{?this.name?=?name;?}
??//?Methods
??abstract?public?void?Add(Component?c);
??abstract?public?void?Remove(?Component?c?);
??abstract?public?void?Display(?int?depth?);
}
//?"Composite"
class?Composite?:?Component
{
??//?Fields
??private?ArrayList?children?=?new?ArrayList();
??//?Constructors
??public?Composite(?string?name?)?:?base(?name?)?{}
??//?Methods
??public?override?void?Add(?Component?component?)
??{?children.Add(?component?);?}
??
??public?override?void?Remove(?Component?component?)
??{?children.Remove(?component?);?}
??
??public?override?void?Display(?int?depth?)
??{?
????Console.WriteLine(?new?String(?'-',?depth?)?+?name?);
????//?Display?each?of?the?node's?children
????foreach(?Component?component?in?children?)
??????component.Display(?depth?+?2?);
??}
}
//?"Leaf"
class?Leaf?:?Component
{
??//?Constructors
??public?Leaf(?string?name?)?:?base(?name?)?{}
??//?Methods
??public?override?void?Add(?Component?c?)
??{?Console.WriteLine("Cannot?add?to?a?leaf");?}
??public?override?void?Remove(?Component?c?)
??{?Console.WriteLine("Cannot?remove?from?a?leaf");?}
??public?override?void?Display(?int?depth?)
??{?Console.WriteLine(?new?String(?'-',?depth?)?+?name?);?}
}
/**////?<summary>
///?Client?test
///?</summary>public?class?Client
{
??public?static?void?Main(?string[]?args?)
??{
????//?Create?a?tree?structure
????Composite?root?=?new?Composite(?"root"?);
????root.Add(?new?Leaf(?"Leaf?A"?));
????root.Add(?new?Leaf(?"Leaf?B"?));
????Composite?comp?=?new?Composite(?"Composite?X"?);
????comp.Add(?new?Leaf(?"Leaf?XA"?)?);
????comp.Add(?new?Leaf(?"Leaf?XB"?)?);
????root.Add(?comp?);
????root.Add(?new?Leaf(?"Leaf?C"?));
????//?Add?and?remove?a?leaf
????Leaf?l?=?new?Leaf(?"Leaf?D"?);
????root.Add(?l?);
????root.Remove(?l?);
????//?Recursively?display?nodes
????root.Display(?1?);
??}
}