模式定義

享元模式主要用於減少建立物件的數量，以減少記憶體佔用和提高效能。

下圖是該模式的類圖：

一個生動的例子

Flyweight抽象類：
public interface Shape {
	void draw();
}

Flyweight具體類：
class Circle implements Shape {
	private String color;
	private int x;
	private int y;
	private int radius;

	public Circle(String color) {
		this.color = color;
 

	}

	public void setX(int x) {
		this.x = x;
	}

	public void setY(int y) {
		this.y = y;
	}

	public void setRadius(int radius) {
		this.radius = radius;
	}

	@Override
	public void draw() {
		System.out.println("Circle: Draw() [Color : " + color + ", x : " + x + ", y :" + y + ", radius :" + radius)
 
;
	}
}

FlyweightFactory類：
public class ShapeFactory {
	private static final Map<String, Circle> CIRCLE_MAP = new HashMap<>();

	public static Circle getCircle(String color) {
		Circle circle = CIRCLE_MAP.get(color);
		if (circle == null) {
			circle = new Circle(color);
			CIRCLE_MAP.
 
put(color, circle);
			System.out.println("Creating circle of color : " + color);
		}
		return circle;
	}
}

客戶端：
public class FlyweightTest {
	private static final String CORLORS[] = { "Red", "Green", "Blue", "White", "Black" };
	private static int length = CORLORS.length;

	public static void main(String[] args) {
		for (int i = 0; i < 20; i++) {
			Circle circle = ShapeFactory.getCircle(getRandomColor());
			circle.setX(getRandomX());
			circle.setY(getRandomY());
			circle.setRadius(100);
			circle.draw();
		}
	}

	private static String getRandomColor() {
		return CORLORS[(int) (Math.random() * length)];
	}

	private static int getRandomX() {
		return (int) (Math.random() * 100);
	}

	private static int getRandomY() {
		return (int) (Math.random() * 100);
	}
}

參考

1. Head First 設計模式[書籍]
2. 菜鳥教程之享元模式
3. 部落格園之享元模式