Java设计模式--享元模式

享元模式主要是利用对对象的重复使用来减低内存的使用，主要思想是建立一个类似对象池的东西，对池内对象实现充分复用。简单实现：

抽象接口

public interface Shape {
    void draw();
}

具体实现

public class Circle implements Shape{
    private String color;
    private int x,y,r;

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

    public void setXYR(int x,int y,int r){
        this.x = x;
        this.y = y;
        this.r = r;
    }

    @Override
    public void draw() {
        System.out.println("draw circle: x = " + x + " , y = " + y + " , r = " + r + " , color = " + color);
    }
}

对象池管理类，对外提供对象

public class ShapeFactory {
    private static final HashMap<String,Shape> map = new HashMap<>();

    public static Shape getCircle(String color){
        Circle circle = (Circle) map.get(color);

        if(circle == null){
            circle = new Circle(color);
            map.put(color,circle);
            System.out.println("create circle : " + color);
        }

        return circle;
    }
}

测试类

public class test {
    private static final String colors[] =
            { "Red", "Green", "Blue"};
    public static void main(String[] args) {
        for(int i=0; i < 10; ++i) {
            Circle circle =
                    (Circle) ShapeFactory.getCircle(getRandomColor());
            circle.setXYR(getRandomX(),getRandomY(),10);
            circle.draw();
        }
    }
    private static String getRandomColor() {
        return colors[(int)(Math.random()*colors.length)];
    }
    private static int getRandomX() {
        return (int)(Math.random()*100 );
    }
    private static int getRandomY() {
        return (int)(Math.random()*100);
    }
}

结果：

create circle : Red
draw circle: x = 58 , y = 99 , r = 10 , color = Red
create circle : Blue
draw circle: x = 58 , y = 24 , r = 10 , color = Blue
create circle : Green
draw circle: x = 82 , y = 45 , r = 10 , color = Green
draw circle: x = 99 , y = 61 , r = 10 , color = Green
draw circle: x = 36 , y = 51 , r = 10 , color = Blue
draw circle: x = 41 , y = 71 , r = 10 , color = Green
draw circle: x = 2 , y = 3 , r = 10 , color = Green
draw circle: x = 35 , y = 74 , r = 10 , color = Green
draw circle: x = 25 , y = 74 , r = 10 , color = Green
draw circle: x = 0 , y = 29 , r = 10 , color = Green

可以发现，虽然我们调用了10次draw，每次circle对象的属性都不同，但是我们只实例化了3个对象，这样在打了频繁的调用某些类似对象时，能极大的减少资源消耗