结构型--享元模式

╰+哭是因爲堅強的太久メ 2021-09-23 01:12 230阅读 0赞

## 概念 ##

--------------------

运用共享技术有效地支持大量细粒度的对象。  
 享元模式的主要目的是实现对象的共享，即共享池，当系统中对象多的时候用这个模式可以减少内存的开销，避免内存溢出，减少重复代码量，通常与工厂模式一起使用。该模式用来减少需要创建的对象的数量（共享池中有一样的就直接返回），以减少内存占用和提高性能。  
 系统中有大量对象，每个对象的状态/成员大部分是外部状态，如果去掉外部状态，就可以用很少的共享对象来代替原系统对象，则把共享部分放在共享池中；创建对象时，享元模式尝试重用共享池中已有的对象，如果未找到匹配的对象，才会去创建新的对象。之后，外部状态作为对象方法的参数来为对象配置外部环境。

优点：

1.  大大减少对象的创建，降低系统的内存，使效率提高。

缺点：

1.  提高了系统的复杂度，需要分离出外部状态和内部状态，内部状态存储于享元中，不随外部场景而变，外部状态取决于场景，随场景而变化。

## 举例 ##

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package flyweight ;
    
    import java.util.Vector;
    public class User {
    	public static void main(String[] args) {
    		FlyweightFactory flyweightFactory = new FlyweightFactory();
    		Glyph glyph = null;
    		CharacterContext characterContext = null;
    		for(int i = 0; i < 5; i++) {
    			glyph = flyweightFactory.CreateCharacter((char)(i+97));
    			characterContext = new CharacterContext(
    					ProduceContext.getRandomNumber(),
    					ProduceContext.getRandomNumber(),
    					ProduceContext.getRandomColor());
    			glyph.draw(characterContext);
    	     }
        }
    }
    
    //产生状态信息的类(与模式无关)
    class ProduceContext{
    	private static final String colors[] = { "Red", "Green", "Blue", "White", "Black" };
    	public static String getRandomColor() {
    	     return colors[(int)(Math.random()*colors.length)];
    	}
    	public static int getRandomNumber() {
    		 return (int)(Math.random()*100 );
    	}
    }
    
    //Character的外部状态信息类
    class CharacterContext {
    	protected String color;
    	protected int x;
    	protected int y;
    	public CharacterContext() { }
    	public CharacterContext(int x, int y, String color) {
    		this.x = x;
    		this.y = y;
    		this.color = color; 
    	}
    	public int getX() {
    		return x;
    	}
    	public int getY() {
    		return y;
    	}
    	public String getColor() {
    		return color;
    	}
    }
    
    //Flyweight接口,实现类可以是可共享对象也可以是不可共享对象
    interface Glyph { 
    	void draw(CharacterContext circleContext);
    }
    
    /*该可共享类在每一个场景中都可作为一个独立的对象
    因为，尽管对象一样，但对象调用方法时所处的环境是不同的
    ConcreteFlyweight类,Flyweight的实现类
    */
    class Character_1 implements Glyph {
    	private char c;//内部状态信息，被共享的量
    	public Character_1(char c) {
    		this.c = c;
    	}
    	public char getChar() {
    		return c;
    	}
    	public void draw(CharacterContext circleContext) {
    		 System.out.println("Character: Draw() [Color : " + circleContext.getColor()
    				 +", x : " + circleContext.getX() +", y :" + circleContext.getY()
    				 +", Character: "+ c+" ]");
    	}
    }
    
    //UnsharedConcreteFlyweight类,Flyweight的实现类
    class Row implements Glyph {
    	public void draw(CharacterContext circleContext) {
    		System.out.println("UnsharedConcreteFlyweight Row");
    	}
    }
    class Column implements Glyph {
    	public void draw(CharacterContext circleContext) {
    		System.out.println("UnsharedConcreteFlyweight Column");
    	}
    }
    
    //FlyweightFactory,用来创建flyweight对象
    class FlyweightFactory {
    	private static final Vector<Glyph> GlyphPool = new Vector<>(26);
    	public FlyweightFactory() {
    		for(char i = 'a'; i <= 'z'; i++) {
    			GlyphPool.add(new Character_1(i));
    		}
    	}
    	public Character_1 CreateCharacter(char c) {
    		Character_1 character = null;
    		int flag = 0;
    		for(Glyph glyph : FlyweightFactory.GlyphPool) {
    			Character_1 ch = (Character_1)glyph;
    			if(ch.getChar() == c) {
    				flag = 1;
    				character = ch;
    				break;
    			}
    		}
    		if(flag == 0) {
    			character = new Character_1(c);
    			GlyphPool.add(character);
    		}
    		return character;
    	}
    	public Row CreateRow() {
    		return new Row();
    	}
    	public Column CreateColumn() {
    		return new Column();
    	}
    	//test,查看是否没有创建已有对象
    	public static void showPool() {
    		for(Glyph g : FlyweightFactory.GlyphPool) {
    			Character_1 ch = (Character_1)g;
    			System.out.println(ch.getChar());
    		}
    	}
    }
    
    Output：
    Character: Draw() [Color : Green, x : 75, y :23, Character: a ]
    Character: Draw() [Color : Blue, x : 59, y :66, Character: b ]
    Character: Draw() [Color : Red, x : 26, y :92, Character: c ]
    Character: Draw() [Color : Green, x : 10, y :90, Character: d ]
    Character: Draw() [Color : Blue, x : 87, y :11, Character: e ]