定义
享元模式（Flyweight Pattern），又称轻量级模式（这也是其英文名为FlyWeight的原因），通过共享技术有效地实现了大量细粒度对象的复用。
内部状态：在享元对象内部不随外界环境改变而改变的共享部分。
外部状态：随着环境的改变而改变，不能够共享的状态就是外部状态。
角色
- FlyWeight 享元接口或者（抽象享元类），定义共享接口
- ConcreteFlyWeight 具体享元类，该类实例将实现共享
- UnSharedConcreteFlyWeight 非共享享元实现类
- FlyWeightFactory 享元工厂类，控制实例的创建和共享
实例
享元接口
public interface Shape {
void draw();
}
具体享元类
public class Circle implements Shape {
String color;
public Circle(String color) {
this.color = color;
}
@Override
public void draw() {
System.out.println("draw a circle, and the color is "+color);
}
}
享元工厂类
public class ShapeFactory {
public int SUM=0;
public int SUM_OBJECT=0;
public static ConcurrentHashMap<String, Shape> map = new ConcurrentHashMap<String, Shape>();
public Shape getShape(String color){
if (map.get(color) == null) {
synchronized (map) {
if (map.get(color) == null) {
map.put(color, new Circle(color));
SUM_OBJECT++;
}
}
}
SUM++;
return map.get(color);
}
}
测试代码
public class Test {
public static void main(String[] args) {
ShapeFactory factory = new ShapeFactory();
factory.getShape("red").draw();
factory.getShape("black").draw();
factory.getShape("blue").draw();
factory.getShape("green").draw();
factory.getShape("red").draw();
factory.getShape("blue").draw();
factory.getShape("red").draw();
System.out.println("共画了"+factory.SUM+"个圆");
System.out.println("共产生了"+factory.SUM_OBJECT+"个对象");
}
}
运行结果
draw a circle, and the color is red
draw a circle, and the color is black
draw a circle, and the color is blue
draw a circle, and the color is green
draw a circle, and the color is red
draw a circle, and the color is blue
draw a circle, and the color is red
共画了7个圆
共产生了4个对象
