享元模式(flyweight)

定义：

• 以共享的方式高效地支持大量细粒度对象的重用

核心：

• 享元对象能做到共享的关建是区分了内部状态和外部状态。

  • 内部状态：可以共享，不会随环境变化而变化

  • 外部状态：不可以共享，会随环境变化而改变

例如我们要在森林中种树

package designmode.flyweight;
public class Tree {

    private final String name;
    private final String data;

    public String getName() {
        return name;
    }

    public String getData() {
        return data;
    }
    public Tree(String name, String data) {
        System.out.printf("%s创建成功",name);
        this.name = name;
        this.data = data;
    }
}

package designmode.flyweight;
public class TreeNode {
    public int getX() {
        return x;
    }
    public void setX(int x) {
        this.x = x;
    }
    public int getY() {
        return y;
    }
    public void setY(int y) {
        this.y = y;
    }
    public Tree getTree() {
        return tree;
    }
    public void setTree(Tree tree) {
        this.tree = tree;
    }

    public TreeNode(int x, int y, Tree tree) {
        super();
        this.x = x;
        this.y = y;
        this.tree = tree;
    }
    private int x;
    private int y;
    private Tree tree;
}

package designmode.flyweight;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
public class TreeFactory {
    private static Map<String,Tree> map = new ConcurrentHashMap<>();
    public static Tree getTree(String name,String data) {
        if(map.containsKey(name)) {
            return map.get(name);
        }
        Tree tree = new Tree(name, data);
        map.put(name, tree);
        return tree;
    }
}

package designmode.flyweight;
public class Client {
    public static void main(String[] args) {
        TreeNode node = new TreeNode(12,23,TreeFactory.getTree("松树", "30年的松树"));
        TreeNode node1 = new TreeNode(2,12,TreeFactory.getTree("松树", "20年的树"));
    }
}

享元模式实现：

• FlyweightFactory享元工厂类：

  • 创建并管理享元对象，享元池一般设计成键值对

  • FlyWeight抽象享元类：

  • 通常是一个接口或抽象类，声明公共方法，这些方法可以向外界提供对象的内部状态，设置外部状态。

  • ConcreteFlyWeight具体享元类：

  • 为内部状态提供成员变量进行存储

  • UnsharedConccreteFlyWeight非共享享元类：

  • 不能被共享的子类可以设计为非共享享元类

来自为知笔记(Wiz)