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深入剖析設(shè)計(jì)模式中的組合模式應(yīng)用及在C++中的實(shí)現(xiàn)

來(lái)源：本站原創(chuàng)|時(shí)間：2020-01-10|欄目：C語(yǔ)言|點(diǎn)擊： 次

組合模式將對(duì)象組合成樹(shù)形結(jié)構(gòu)以表示“部分-整體”的層次結(jié)構(gòu)。C o m p o s i t e 使得用戶對(duì)單個(gè)對(duì)象和組合對(duì)象的使用具有一致性。

模式圖：

適用場(chǎng)景：

  • 你想表示對(duì)象的部分-整體層次結(jié)構(gòu)。
  • 你希望用戶忽略組合對(duì)象與單個(gè)對(duì)象的不同，用戶將統(tǒng)一地使用組合結(jié)構(gòu)中的所有對(duì)象。

舉例：

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(duì)象可以包含其它Component類型的對(duì)象。換而言之，Composite類型對(duì)象可以含有其它的樹(shù)枝（Composite）類型或樹(shù)葉（Leaf）類型的對(duì)象。

合成模式的實(shí)現(xiàn)根據(jù)所實(shí)現(xiàn)接口的區(qū)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(duì)象的管理方法，但合成模式必須在合適的地方提供子對(duì)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(lái)管理子類對(duì)象的方法，包括add（）、remove（），以及getChild（）方法。這樣做的好處是所有的構(gòu)件類都有相同的接口。在客戶端看來(lái)，樹(shù)葉類對(duì)象與合成類對(duì)象的區(qū)別起碼在接口層次上消失了，客戶端可以同等同的對(duì)待所有的對(duì)象。這就是透明形式的合成模式。

這個(gè)選擇的缺點(diǎn)是不夠安全，因?yàn)闃?shù)葉類對(duì)象和合成類對(duì)象在本質(zhì)上是有區(qū)別的。樹(shù)葉類對(duì)象不可能有下一個(gè)層次的對(duì)象，因此add（）、remove（）以及getChild（）方法沒(méi)有意義，是在編譯時(shí)期不會(huì)出錯(cuò)，而只會(huì)在運(yùn)行時(shí)期才會(huì)出錯(cuò)。

安全方式

第二種選擇是在Composite類里面聲明所有的用來(lái)管理子類對(duì)象的方法。這樣的做法是安全的做法，因?yàn)闃?shù)葉類型的對(duì)象根本就沒(méi)有管理子類對(duì)象的方法，因此，如果客戶端對(duì)樹(shù)葉類對(duì)象使用這些方法時(shí)，程序會(huì)在編譯時(shí)期出錯(cuò)。

這個(gè)選擇的缺點(diǎn)是不夠透明，因?yàn)闃?shù)葉類和合成類將具有不同的接口。

這兩個(gè)形式各有優(yōu)缺點(diǎn)，需要根據(jù)軟件的具體情況做出取舍決定。

安全式的合成模式實(shí)現(xiàn): 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(shí)現(xiàn): 每個(gè)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 );
 }
}

實(shí)例

再看看一個(gè)完整些的例子：

#include <iostream> 
#include <string> 
#include <list> 
using namespace std; 
 
class Component 
{ 
protected: 
  string name; 
public: 
  Component(string name) 
    :name(name) 
  {  } 
  virtual void AddComponent(Component *component) {  } 
  virtual void RemoveComponent(Component *component) {  } 
  virtual void GetChild(int depth)  { } 
}; 
 
class Leaf: public Component 
{ 
public: 
  Leaf(string name) 
    :Component(name) 
  {  } 
  void AddComponent(Component *component) 
  { 
    cout<<"Leaf can't add component"<<endl; 
  } 
  void RemoveComponent(Component *component) 
  { 
    cout<<"Leaf can't remove component"<<endl; 
  } 
  void GetChild(int depth) 
  { 
    string _tmpstring(depth, '-'); 
    cout<<_tmpstring<<name<<endl; 
  } 
}; 
 
class Composite:public Component 
{ 
private: 
  list<Component*> _componets; 
 
public: 
  Composite(string name) 
    :Component(name) 
  { } 
  void AddComponent(Component *component) 
  { 
    _componets.push_back(component); 
  } 
  void RemoveComponent(Component *component) 
  { 
    _componets.remove(component); 
  } 
  void GetChild(int depth) 
  { 
    string tmpstring (depth, '-'); 
    cout<<tmpstring<<name<<endl; 
    list<Component*>::iterator iter = _componets.begin(); 
    for(; iter != _componets.end(); iter++) 
    { 
      (*iter)->GetChild(depth + 2); 
    } 
  } 
}; 
 
int main() 
{ 
  Composite *root = new Composite("root"); 
  Leaf *leaf1 = new Leaf("leaf1"); 
  Leaf *leaf2 = new Leaf("leaf2"); 
  root->AddComponent(leaf1); 
  root->AddComponent(leaf2); 
 
  Composite *lay2 = new Composite("layer2"); 
  Leaf *leaf4 = new Leaf("leaf4"); 
  lay2->AddComponent(leaf4); 
 
  Composite *lay1 = new Composite("layer1"); 
  Leaf *leaf3 = new Leaf("leaf3"); 
  lay1->AddComponent(leaf3); 
  lay1->AddComponent(lay2); 
 
  root->AddComponent(lay1); 
 
  root->GetChild(1); 
  cout<<endl; 
  lay1->GetChild(1); 
  cout<<endl; 
  lay2->GetChild(1); 
 
  delete root; 
  delete lay1; 
  delete lay2; 
  delete leaf1; 
  delete leaf2; 
  delete leaf3; 
  delete leaf4; 
  system("pause"); 
  return 0; 
}

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