Приспособленец (шаблон проектирования)

Приспособленец
Flyweight
Тип	структурный
Описан в Design Patterns	Да

Приспособленец (англ. flyweight, «легковесный (элемент)») — структурный шаблон проектирования, при котором объект, представляющий себя как уникальный экземпляр в разных местах программы, по факту не является таковым.

Цель

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

Описание

Приспособленец используется для уменьшения затрат при работе с большим количеством мелких объектов. При проектировании приспособленеца 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.

Приспособленец дополняет шаблон фабрика таким образом, что при обращении клиента к фабрике 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 на Python

Исходный текст на языке Python

                                                                     
class Lamp(object):
    def __init__(self, color):
        self.color = color


class LampFactory:
    lamps = dict()

    @staticmethod
    def get_lamp(color):
        return LampFactory.lamps.setdefault(color, Lamp(color))


class TreeBranch(object):
    def __init__(self, branch_number):
        self.branch_number = branch_number

    def hang(self, lamp):
        print(f"Hang ${lamp.color} [${id(lamp)}] lamp on branch ${self.branch_number} [${id(self)}]")


class ChristmasTree(object):
    def __init__(self):
        self.lamps_hung = 0
        self.branches = {}

    def get_branch(self, number):
        return self.branches.setdefault(number, TreeBranch(number))

    def dress_up_the_tree(self):
        self.hang_lamp("red", 1)
        self.hang_lamp("blue", 1)
        self.hang_lamp("yellow", 1)
        self.hang_lamp("red", 2)
        self.hang_lamp("blue", 2)
        self.hang_lamp("yellow", 2)
        self.hang_lamp("red", 3)
        self.hang_lamp("blue", 3)
        self.hang_lamp("yellow", 3)
        self.hang_lamp("red", 4)
        self.hang_lamp("blue", 4)
        self.hang_lamp("yellow", 4)
        self.hang_lamp("red", 5)
        self.hang_lamp("blue", 5)
        self.hang_lamp("yellow", 5)
        self.hang_lamp("red", 6)
        self.hang_lamp("blue", 6)
        self.hang_lamp("yellow", 6)
        self.hang_lamp("red", 7)
        self.hang_lamp("blue", 7)
        self.hang_lamp("yellow", 7)

    def hang_lamp(self, color, branch_number):
        self.get_branch(branch_number).hang(LampFactory.get_lamp(color))
        self.lamps_hung += 1


if __name__ == '__main__':
    ChristmasTree().dress_up_the_tree()

Пример на Python (с переопределением конструктора)

Исходный текст на языке Python (с переопределением конструктора)

                                                                     
class Lamp(object):
    __instances = dict()
    
    def __new__(cls, color):
        return cls.__instances.setdefault(color, super().__new__(cls))

    def __init__(self, color):
        self.color = color

class TreeBranch(object):
    def __init__(self, branch_number):
        self.branch_number = branch_number

    def hang(self, lamp):
        print(f"Hang ${lamp.color} [${id(lamp)}] lamp on branch ${self.branch_number} [${id(self)}]")


class ChristmasTree(object):
    def __init__(self):
        self.lamps_hung = 0
        self.branches = {}

    def get_branch(self, number):
        return self.branches.setdefault(number, TreeBranch(number))

    def dress_up_the_tree(self):
        for branch in range(1, 8):
            for color in "red", "blue", "yellow":
                self.hang_lamp(color, branch)

    def hang_lamp(self, color, branch_number):
        self.get_branch(branch_number).hang(Lamp(color))
        self.lamps_hung += 1


if __name__ == '__main__':
    ChristmasTree().dress_up_the_tree()

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

public abstract class EnglishCharacter {

	protected char symbol;
	
	protected int width;
	
	protected int height;
	
	public abstract void printCharacter();
	
}

public class CharacterA extends EnglishCharacter {

	public CharacterA(){
		symbol = 'A';
		width = 10;
		height = 20;
	}
	
	@Override
	public void printCharacter() {
		System.out.println("Symbol = " + symbol + " Width = " + width + " Height = " + height);
	}
	
}

public class CharacterB extends EnglishCharacter {

	public CharacterB(){
		symbol = 'B';
		width = 20;
		height = 30;
	}
	
	@Override
	public void printCharacter() {
		System.out.println("Symbol = " + symbol + " Width = " + width + " Height = " + height);
	}
	
}

public class CharacterC extends EnglishCharacter {

	public CharacterC(){
		symbol = 'C';
		width = 40;
		height = 50;
	}
	
	@Override
	public void printCharacter() {
		System.out.println("Symbol = " + symbol + " Width = " + width + " Height = " + height);
	}
	
}

public class FlyweightFactory {

	private HashMap<Integer, EnglishCharacter> characters = new HashMap();
	
	public EnglishCharacter getCharacter(int characterCode){
		EnglishCharacter character = characters.get(characterCode);
		if (character == null){
			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;
	} 
	
}

/* 
 * Класс, показывающий работу шаблона проектирования "Приспособленец".
 * */

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 virtual void Display(int pointSize)
    {
      this.pointSize = pointSize;
      Console.WriteLine(this.symbol +
        " (pointsize " + this.pointSize + ")");
    }
  }

  // "ConcreteFlyweight"

  class CharacterA : Character
  {
    // Constructor
    public CharacterA()
    {
      this.symbol = 'A';
      this.height = 100;
      this.width = 120;
      this.ascent = 70;
      this.descent = 0;
    }
  }

  // "ConcreteFlyweight"

  class CharacterB : Character
  {
    // Constructor
    public CharacterB()
    {
      this.symbol = 'B';
      this.height = 100;
      this.width = 140;
      this.ascent = 72;
      this.descent = 0;
    }
  }

  // ... 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;
    }
  }
}

Пример на C++

Исходный текст на языке C++

#include <map>
#include <iostream>
#include <memory>
// "Flyweight"
class Character
{
public:
    virtual ~Character() = default;
    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;
        mWidth = 120;
        mHeight = 100;
        mAscent = 70;
        mDescent = 0;
        mPointSize = aPointSize;
    }

    // from Character
    virtual void display() const {
        std::cout << mSymbol << " ( PointSize " << mPointSize << " )\n";
    }
};

// "FlyweightFactory"
template < const int POINT_SIZE >
class CharacterFactory
{
public:
    const Character& getCharacter( char aKey )
    {
        // Uses "lazy initialization"
        Characters::const_iterator it = mCharacters.find( aKey );
        if ( mCharacters.end() == it ) {
             mCharacters[aKey] = std::make_unique<const ConcreteCharacter>(aKey, POINT_SIZE);
            return *mCharacters[aKey];
        } else {
            return *it->second;
        }
    }

private:
    using Characters = std::map < char, std::unique_ptr<const Character> >;
    Characters mCharacters;
};

int main(){
    std::string document = "AAZZBBZB";

    CharacterFactory<12> characterFactory;

    for (auto it :document){
        auto&& 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

Пример на Ruby

Исходный текст на языке Ruby

# Объект Приспособленец
class Lamp
  attr_reader :color
  #attr_reader makes color attribute available outside 
  #of the class by calling .color on a Lamp instance
 
  def initialize(color)
    @color = color
  end
end
 
class TreeBranch
  def initialize(branch_number)
    @branch_number = branch_number
  end
 
  def hang(lamp)
    puts "Hang #{lamp.color} lamp on branch #{@branch_number}"
  end
end
 
# Flyweight Factory
class LampFactory
  def initialize
    @lamps = {}
  end
 
  def find_lamp(color)
    if @lamps.has_key?(color)
      # if the lamp already exists, reference it instead of creating a new one
      lamp = @lamps[color]
    else
      lamp = Lamp.new(color)
      @lamps[color] = lamp
    end
    lamp
  end
 
  def total_number_of_lamps_made
    @lamps.size
  end
end
 
class ChristmasTree
  def initialize
    @lamp_factory = LampFactory.new
    @lamps_hung = 0
 
    dress_up_the_tree
  end
 
  def hang_lamp(color, branch_number)
    TreeBranch.new(branch_number).hang(@lamp_factory.find_lamp(color))
    @lamps_hung += 1
  end
 
  def dress_up_the_tree
    hang_lamp('red', 1)
    hang_lamp('blue', 1)
    hang_lamp('yellow', 1)
    hang_lamp('red', 2)
    hang_lamp('blue', 2)
    hang_lamp('yellow', 2)
    hang_lamp('red', 3)
    hang_lamp('blue', 3)
    hang_lamp('yellow', 3)
    hang_lamp('red', 4)
    hang_lamp('blue', 4)
    hang_lamp('yellow', 4)
    hang_lamp('red', 5)
    hang_lamp('blue', 5)
    hang_lamp('yellow', 5)
    hang_lamp('red', 6)
    hang_lamp('blue', 6)
    hang_lamp('yellow', 6)
    hang_lamp('red', 7)
    hang_lamp('blue', 7)
    hang_lamp('yellow', 7)
    puts "Made #{@lamp_factory.total_number_of_lamps_made} total lamps"
  end
end

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 C++.