Приспособленец (шаблон проектирования)

Шаблон проектирования

Приспособленец
Flyweight
Тип:	структурный
Описан в Design Patterns	Да

Приспособленец (англ. Flyweight) — это объект, представляющий себя как уникальный экземпляр в разных местах программы, но по факту не являющийся таковым.

Цель

Оптимизация работы с памятью, путем предотвращения создания экземпляров элементов, имеющих общую сущность.

Описание

Flyweight используется для уменьшения затрат при работе с большим количеством мелких объектов. При проектировании приспособленца необходимо разделить его свойства на внешние и внутренние. Внутренние свойства всегда неизменны, тогда как внешние могут отличаться в зависимости от места и контекста применения и должны быть вынесены за пределы приспособленца.

Flyweight дополняет паттерн Factory таким образом, что Factory при обращении к ней клиента для создания нового объекта ищет уже созданный объект с такими же параметрами, что и у требуемого, и возвращает его клиенту. Если такого объекта нет, то фабрика создаст новый.

Примеры

Пример #1 на Java

Исходный текст на языке Java

import java.util.*;
 
public enum FontEffect {
    BOLD, ITALIC, SUPERSCRIPT, SUBSCRIPT, STRIKETHROUGH
}
 
public final class FontData {
    /**
     * A weak hash map will drop unused references to FontData.
     * Values have to be wrapped in WeakReferences, 
     * because value objects in weak hash map are held by strong references.
     */
    private static final WeakHashMap<FontData, WeakReference<FontData>> flyweightData =
        new WeakHashMap<FontData, WeakReference<FontData>>();
    private final int pointSize;
    private final String fontFace;
    private final Color color;
    private final Set<FontEffect> effects;
 
    private FontData(int pointSize, String fontFace, Color color, EnumSet<FontEffect> effects) {
        this.pointSize = pointSize;
        this.fontFace = fontFace;
        this.color = color;
        this.effects = Collections.unmodifiableSet(effects);
    }
 
    public static FontData create(int pointSize, String fontFace, Color color,
        FontEffect... effects) {
        EnumSet<FontEffect> effectsSet = EnumSet.noneOf(FontEffect.class);
        effectsSet.addAll(Arrays.asList(effects));
        // We are unconcerned with object creation cost, we are reducing overall memory consumption
        FontData data = new FontData(pointSize, fontFace, color, effectsSet);
        if (!flyweightData.containsKey(data)) {
            flyweightData.put(data, new WeakReference<FontData> (data));
        }
        // return the single immutable copy with the given values
        return flyweightData.get(data).get();
    }
 
    @Override
    public boolean equals(Object obj) {
        if (obj instanceof FontData) {
            if (obj == this) {
                return true;
            }
            FontData other = (FontData) obj;
            return other.pointSize == pointSize && other.fontFace.equals(fontFace)
                && other.color.equals(color) && other.effects.equals(effects);
        }
        return false;
    }
 
    @Override
    public int hashCode() {
        return (pointSize * 37 + effects.hashCode() * 13) * fontFace.hashCode();
    }
 
    // Getters for the font data, but no setters. FontData is immutable.
}

Пример #2 на Java

Исходный текст на языке Java

package com.designpatterns.flyweight;
 
/* Файл EnglishCharacter.java
 * 
 * */
 
public abstract class EnglishCharacter {
 
        protected char simbol;
 
        protected int width;
 
        protected int height;
 
        public abstract void printCharacter();
 
}
 
 
package com.designpatterns.flyweight;
 
/* Файл CharacterA.java
 * 
 * */
 
public class CharacterA extends EnglishCharacter {
 
        public CharacterA(){
                simbol = 'A';
                width = 10;
                height = 20;
        }
 
        @Override
        public void printCharacter() {
                System.out.println("Simbol = " + simbol + " Width = " + width + " Height = " + height);
        }
 
}
 
 
package com.designpatterns.flyweight;
 
/* Файл CharacterB.java
 * 
 * */
 
public class CharacterB extends EnglishCharacter {
 
        public CharacterB(){
                simbol = 'B';
                width = 20;
                height = 30;
        }
 
        @Override
        public void printCharacter() {
                System.out.println("Simbol = " + simbol + " Width = " + width + " Height = " + height);
        }
 
}
 
 
package com.designpatterns.flyweight;
 
/* Файл CharacterC.java
 * 
 * */
 
public class CharacterC extends EnglishCharacter {
 
        public CharacterC(){
                simbol = 'C';
                width = 40;
                height = 50;
        }
 
        @Override
        public void printCharacter() {
                System.out.println("Simbol = " + simbol + " Width = " + width + " Height = " + height);
        }
 
}
 
 
package com.designpatterns.flyweight;
 
/* Файл FlyweightFactory.java
 * 
 * */
 
import java.util.HashMap;
 
public class FlyweightFactory {
 
        private HashMap<Integer, EnglishCharacter> characters = new HashMap<Integer, EnglishCharacter>();
 
        public EnglishCharacter getCharacter(int characterCode){
                EnglishCharacter character = characters.get(new Integer(characterCode));
                if (null == character){
                        switch (characterCode){
                                case 1 : {
                                        character = new CharacterA();
                                        break;
                                }
                                case 2 : {
                                        character = new CharacterB();
                                        break;
                                }
                                case 3 : {
                                        character = new CharacterC();
                                        break;
                                }
                        }
                        characters.put(characterCode, character);
                }
                return character;
        } 
 
}
 
 
package com.designpatterns.flyweight;
 
/* Класс, показывающий работу шаблона проектирования "Приспособленец".
 * Файл Application.java
 * 
 * */
 
public class Application {
 
        public static void main (String [] args){
                FlyweightFactory factory = new FlyweightFactory();
 
                int [] characterCodes = {1,2,3};
                for (int nextCode : characterCodes){
                        EnglishCharacter character = factory.getCharacter(nextCode);
                        character.printCharacter();
                }
        }
 
}

Пример на C#

Исходный текст на языке C#

using System;
using System.Collections;
 
namespace Flyweight
{
 
  class MainApp
  {
    static void Main()
    {
      // Build a document with text
      string document = "AAZZBBZB";
      char[] chars = document.ToCharArray();
 
      CharacterFactory f = new CharacterFactory();
 
      // extrinsic state
      int pointSize = 10;
 
      // For each character use a flyweight object
      foreach (char c in chars)
      {
        pointSize++;
        Character character = f.GetCharacter(c);
        character.Display(pointSize);
      }
 
      // Wait for user
      Console.Read();
    }
  }
 
  // "FlyweightFactory"
 
  class CharacterFactory
  {
    private Hashtable characters = new Hashtable();
 
    public Character GetCharacter(char key)
    {
      // Uses "lazy initialization"
      Character character = characters[key] as Character;
      if (character == null)
      {
        switch (key)
        {
          case 'A': character = new CharacterA(); break;
          case 'B': character = new CharacterB(); break;
            //...
          case 'Z': character = new CharacterZ(); break;
        }
        characters.Add(key, character);
      }
      return character;
    }
  }
 
  // "Flyweight"
 
  abstract class Character
  {
    protected char symbol;
    protected int width;
    protected int height;
    protected int ascent;
    protected int descent;
    protected int pointSize;
 
    public abstract void Display(int pointSize);
  }
 
  // "ConcreteFlyweight"
 
  class CharacterA : Character
  {
    // Constructor
    public CharacterA()
    {
      this.symbol = 'A';
      this.height = 100;
      this.width = 120;
      this.ascent = 70;
      this.descent = 0;
    }
 
    public override void Display(int pointSize)
    {
      this.pointSize = pointSize;
      Console.WriteLine(this.symbol +
        " (pointsize " + this.pointSize + ")");
    }
  }
 
  // "ConcreteFlyweight"
 
  class CharacterB : Character
  {
    // Constructor
    public CharacterB()
    {
      this.symbol = 'B';
      this.height = 100;
      this.width = 140;
      this.ascent = 72;
      this.descent = 0;
    }
 
    public override void Display(int pointSize)
    {
      this.pointSize = pointSize;
      Console.WriteLine(this.symbol +
        " (pointsize " + this.pointSize + ")");
    }
 
  }
 
  // ... C, D, E, etc.
 
  // "ConcreteFlyweight"
 
  class CharacterZ : Character
  {
    // Constructor
    public CharacterZ()
    {
      this.symbol = 'Z';
      this.height = 100;
      this.width = 100;
      this.ascent = 68;
      this.descent = 0;
    }
 
    public override void Display(int pointSize)
    {
      this.pointSize = pointSize;
      Console.WriteLine(this.symbol +
        " (pointsize " + this.pointSize + ")");
    }
  }
}

Пример на C++

Исходный текст на языке C++

#include <map>
#include <iostream>
 
// "Flyweight"
class Character{
        public: 
                virtual void display() const = 0;
 
        protected: 
                char mSymbol;
                int  mWidth;
                int  mHeight;
                int  mAscent;
                int  mDescent;
                int  mPointSize;
};
 
// "ConcreteFlyweight"
class ConcreteCharacter : public Character{
        public: 
                // Constructor
                ConcreteCharacter( char aSymbol, int aPointSize ){
                        mSymbol         = aSymbol;
                        mHeight         = 100;
                        mWidth          = 120;
                        mAscent         = 70;
                        mDescent        = 0;
                        mPointSize      = aPointSize;
                }
 
                // from Character
                virtual void display() const{
                        std::cout << mSymbol << " ( PointSize " << mPointSize << " )\n";
                }
};
 
 
// "FlyweightFactory"
template< int POINT_SIZE = 10 >
class CharacterFactory{
 
        public: 
                const Character& getCharacter( char aKey ){
                        // Uses "lazy initialization"
                        Characters::const_iterator it = mCharacters.find( aKey );
                        if ( mCharacters.end() == it ){
                                const Character* character = new ConcreteCharacter(aKey, POINT_SIZE);
                                mCharacters[aKey] = character;
                                return *character;
                        }
                        else{
                                return *it->second;
                        }
                }
 
                virtual ~CharacterFactory(){
                        for (Characters::const_iterator it = mCharacters.begin(); it != mCharacters.end(); it++)
                                delete it->second;
                }
 
        private: 
                typedef std::map< char, const Character* > Characters;   
                Characters mCharacters;
};
 
 
int main(){
        std::string document = "AAZZBBZB";
 
        CharacterFactory<12> characterFactory;
 
        for (std::string::const_iterator it = document.begin(); it != document.end(); it++){
                const Character& character = characterFactory.getCharacter( *it );
                character.display();
        }
        return 0;
}

Пример на PHP5

Исходный текст на языке PHP

<?php
 
// "FlyweightFactory"
class CharacterFactory
{
        private $characters = array();
        public function GetCharacter($key)
        {
                // Uses "lazy initialization"
                if (!array_key_exists($key, $this->characters))
                {
                        switch ($key)
                        {
                                case 'A': $this->characters[$key] = new CharacterA(); break;
                                case 'B': $this->characters[$key] = new CharacterB(); break;
                                //...
                                case 'Z': $this->characters[$key] = new CharacterZ(); break;
                        }
                }
                return $this->characters[$key];
        }
}
 
// "Flyweight"
abstract class Character
{
        protected $symbol;
        protected $width;
        protected $height;
        protected $ascent;
        protected $descent;
        protected $pointSize;
 
        public abstract function Display($pointSize);
}
 
// "ConcreteFlyweight"
 
class CharacterA extends Character
{
        // Constructor
        public function __construct()
        {
                $this->symbol = 'A';
                $this->height = 100;
                $this->width = 120;
                $this->ascent = 70;
                $this->descent = 0;
        }
 
        public function Display($pointSize)
        {
                $this->pointSize = $pointSize;
                print ($this->symbol." (pointsize ".$this->pointSize.")");
        }
}
 
// "ConcreteFlyweight"
 
class CharacterB extends Character
{
        // Constructor
        public function __construct()
        {
                $this->symbol = 'B';
                $this->height = 100;
                $this->width = 140;
                $this->ascent = 72;
                $this->descent = 0;
        }
 
        public function  Display($pointSize)
        {
                $this->pointSize = $pointSize;
                print($this->symbol." (pointsize ".$this->pointSize.")");
        }
 
}
 
// ... C, D, E, etc.
 
// "ConcreteFlyweight"
 
class CharacterZ extends Character
{
        // Constructor
        public function __construct()
        {
                $this->symbol = 'Z';
                $this->height = 100;
                $this->width = 100;
                $this->ascent = 68;
                $this->descent = 0;
        }
 
        public function  Display($pointSize)
        {
                $this->pointSize = $pointSize;
                print($this->symbol." (pointsize ".$this->pointSize.")");
        }
}
 
$document="AAZZBBZB";
// Build a document with text
$chars=str_split($document);
print_r($chars);
 
$f = new CharacterFactory();
 
// extrinsic state
$pointSize = 0;
 
// For each character use a flyweight object
foreach ($chars as $key) {
        $pointSize++;
        $character = $f->GetCharacter($key);
        $character->Display($pointSize);
}
 
?>

Пример на VB.NET

Исходный текст на VB.NET

Imports System.Collections
 
Namespace Flyweight
 
    Class Program
        Shared Sub Main()
            ' Build a document with text
            Dim document As String = "AAZZBBZB"
            Dim chars As Char() = document.ToCharArray()
 
            Dim f As New CharacterFactory()
 
            ' extrinsic state
            Dim pointSize As Integer = 10
 
            ' For each character use a flyweight object
            For Each c As Char In chars
                pointSize += 1
                Dim character As Character = f.GetCharacter(c)
                character.Display(pointSize)
            Next
 
            ' Wait for user
            Console.Read()
        End Sub
    End Class
 
    ' "FlyweightFactory"
    Class CharacterFactory
        Private characters As New Hashtable()
 
        Public Function GetCharacter(ByVal key As Char) As Character
            ' Uses "lazy initialization"
            Dim character As Character = TryCast(characters(key), Character)
            If character Is Nothing Then
                Select Case key
                    Case "A"c
                        character = New CharacterA()
                        Exit Select
                    Case "B"c
                        character = New CharacterB()
                        Exit Select
                        '...
                    Case "Z"c
                        character = New CharacterZ()
                        Exit Select
                End Select
                characters.Add(key, character)
            End If
            Return character
        End Function
    End Class
 
    ' "Flyweight"
    MustInherit Class Character
        Protected symbol As Char
        Protected width As Integer
        Protected height As Integer
        Protected ascent As Integer
        Protected descent As Integer
        Protected pointSize As Integer
 
        Public MustOverride Sub Display(ByVal pointSize As Integer)
    End Class
 
    ' "ConcreteFlyweight"
    Class CharacterA
        Inherits Character
        ' Constructor
        Public Sub New()
            Me.symbol = "A"c
            Me.height = 100
            Me.width = 120
            Me.ascent = 70
            Me.descent = 0
        End Sub
 
        Public Overrides Sub Display(ByVal pointSize As Integer)
            Me.pointSize = pointSize
            Console.WriteLine(Me.symbol & " (pointsize " & Me.pointSize & ")")
        End Sub
    End Class
 
    ' "ConcreteFlyweight"
    Class CharacterB
        Inherits Character
        ' Constructor
        Public Sub New()
            Me.symbol = "B"c
            Me.height = 100
            Me.width = 140
            Me.ascent = 72
            Me.descent = 0
        End Sub
 
        Public Overrides Sub Display(ByVal pointSize As Integer)
            Me.pointSize = pointSize
            Console.WriteLine(Me.symbol & " (pointsize " & Me.pointSize & ")")
        End Sub
 
    End Class
 
    ' ... C, D, E, etc.
 
    ' "ConcreteFlyweight"
    Class CharacterZ
        Inherits Character
        ' Constructor
        Public Sub New()
            Me.symbol = "Z"c
            Me.height = 100
            Me.width = 100
            Me.ascent = 68
            Me.descent = 0
        End Sub
 
        Public Overrides Sub Display(ByVal pointSize As Integer)
            Me.pointSize = pointSize
            Console.WriteLine(Me.symbol & " (pointsize " & Me.pointSize & ")")
        End Sub
    End Class
End Namespace

Символы на Smalltalk

Символы в Smalltalk практически идентичны «обычным строкам», но не порождаются каждый раз заново. Два идентичных символа на самом деле всегда являются одним и тем же экземпляром класса Symbol, тогда как две идентичные строки могут быть разными экземплярами класса String.

Ссылки

• Паттерн Flyweight (приспособленец) — назначение, описание, особенности и реализация на С++.