设计模式之享元模式

package designPatterns.structuralPatterns.flyweight;

import java.awt.*;

public class Tree {
    private int x;
    private int y;
    private TreeType type;

    public Tree(int x, int y, TreeType type) {
        this.x = x;
        this.y = y;
        this.type = type;
    }

    public void draw(Graphics g) {
        type.draw(g, x, y);
    }
}

package designPatterns.structuralPatterns.flyweight;

import javax.swing.*;
import java.awt.*;
import java.util.ArrayList;
import java.util.List;

public class Forest extends JFrame {
    private List<Tree> trees = new ArrayList<>();

    public void plantTree(int x, int y, String name, Color color, String otherTreeData) {
        TreeType type = TreeFactory.getTreeType(name, color, otherTreeData);
        Tree tree = new Tree(x, y, type);
        trees.add(tree);
    }

    @Override
    public void paint(Graphics graphics) {
        for (Tree tree : trees) {
            tree.draw(graphics);
        }
    }
}

package designPatterns.structuralPatterns.flyweight;

import java.awt.*;

public class TreeType {
    private String name;
    private Color color;
    private String otherTreeData;

    public TreeType(String name, Color color, String otherTreeData) {
        this.name = name;
        this.color = color;
        this.otherTreeData = otherTreeData;
    }

    public void draw(Graphics g, int x, int y) {
        g.setColor(Color.BLACK);
        g.fillRect(x - 1, y, 3, 5);
        g.setColor(color);
        g.fillOval(x - 5, y - 10, 10, 10);
    }
}

package designPatterns.structuralPatterns.flyweight;

import java.awt.*;
import java.util.HashMap;
import java.util.Map;

public class TreeFactory {
    static Map<String, TreeType> treeTypes = new HashMap<>();

    public static TreeType getTreeType(String name, Color color, String otherTreeData) {
        TreeType result = treeTypes.get(name);
        if (result == null) {
            result = new TreeType(name, color, otherTreeData);
            treeTypes.put(name, result);
        }
        return result;
    }
}

package designPatterns.structuralPatterns.flyweight;

import java.awt.*;

/**
 * 享元是一种结构型设计模式， 它允许你在消耗少量内存的情况下支持大量对象。
 *
 * 模式通过共享多个对象的部分状态来实现上述功能。 换句话来说， 享元会将不同对象的相同数据进行缓存以节省内存。
 *
 * 渲染一片森林
 * 本例中， 我们将渲染一片森林 （1,000,000 棵树）！ 每棵树都由包含一些状态的对象来表示 （坐标和纹理等）。 尽管程序能够完成其主要工作， 但很显然它需要消耗大量内存。
 *
 * 原因很简单： 太多树对象包含重复数据 （名称、 纹理和颜色）。 因此我们可用享元模式来将这些数值存储在单独的享元对象中 （ Tree­Type 类）。 现在我们不再将相同数据存储在数千个 Tree 对象中， 而是使用一组特殊的数值来引用其中一个享元对象。
 *
 * 客户端代码不会知道任何事情， 因为重用享元对象的复杂机制隐藏在了享元工厂中。
 */
public class Demo {
    static int CANVAS_SIZE = 500;
    static int TREES_TO_DRAW = 1000000;
    static int TREE_TYPES = 2;

    public static void main(String[] args) {
        Forest forest = new Forest();
        for (int i = 0; i < Math.floor(TREES_TO_DRAW / TREE_TYPES); i++) {
            forest.plantTree(random(0, CANVAS_SIZE), random(0, CANVAS_SIZE),
                    "Summer Oak", Color.GREEN, "Oak texture stub");
            forest.plantTree(random(0, CANVAS_SIZE), random(0, CANVAS_SIZE),
                    "Autumn Oak", Color.ORANGE, "Autumn Oak texture stub");
        }
        forest.setSize(CANVAS_SIZE, CANVAS_SIZE);
        forest.setVisible(true);

        System.out.println(TREES_TO_DRAW + " trees drawn");
        System.out.println("---------------------");
        System.out.println("Memory usage:");
        System.out.println("Tree size (8 bytes) * " + TREES_TO_DRAW);
        System.out.println("+ TreeTypes size (~30 bytes) * " + TREE_TYPES + "");
        System.out.println("---------------------");
        System.out.println("Total: " + ((TREES_TO_DRAW * 8 + TREE_TYPES * 30) / 1024 / 1024) +
                "MB (instead of " + ((TREES_TO_DRAW * 38) / 1024 / 1024) + "MB)");
    }

    private static int random(int min, int max) {
        return min + (int) (Math.random() * ((max - min) + 1));
    }
}

1000000 trees drawn
---------------------
Memory usage:
Tree size (8 bytes) * 1000000
+ TreeTypes size (~30 bytes) * 2
---------------------
Total: 7MB (instead of 36MB)