设计模式系列:享元模式

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概念

一个类的实例有多种 “虚拟实例”。 虚拟实例通过共享数据的方式存在。

实现

  • 类图：
    图片

Tree:

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package com.littlehui.design.flyweight;

/**
 * Created by littlehui on 2018/1/23.
 */
public class Tree {
    private int x;
    private int y;
    private int age;

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

    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 int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void display() {
        System.out.println("坐标x:" + x + "坐标y:" + y + "年龄age:" + age);
    }
}
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package com.littlehui.design.flyweight;

import java.util.HashMap;
import java.util.Map;

/**
 * Created by littlehui on 2018/1/23.
 */
public class TreeManager {

    Map<String, Tree> allTrees = new HashMap<String, Tree>();

    public Tree createTree(int x, int y, int age) {
        String treeHash = new StringBuffer().append(x).append(y).append(age).toString();
        if (allTrees.get(treeHash) != null) {
            return allTrees.get(treeHash);
        } else {
            Tree tree = new Tree(x, y, age);
            allTrees.put(treeHash, tree);
            return allTrees.get(treeHash);
        }
    }

    public void displayAllTrees() {
        for (String key : allTrees.keySet()) {
            Tree tree = allTrees.get(key);
            tree.display();
        }
    }
}
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package com.littlehui.design.flyweight;

/**
 * Created by littlehui on 2018/1/23.
 */
public class Client {

    public static void main(String[] args) {
        TreeManager treeManager = new TreeManager();
        Tree tree1 = treeManager.createTree(1,2,3);
        Tree tree2 = treeManager.createTree(1,2,3);
        Tree tree3 = treeManager.createTree(1,2,4);

        System.out.println("实例个数：" + "tree1, tree2, tree3");
        System.out.println("真实实例个数：");
        treeManager.displayAllTrees();
    }
}

场景

在java应用中,会出现许多String a=”123”,String b=”123”之类的String类型的变量,如果只是小应用,到还好,假设是一个庞大的系统,有好多处都需要用定义String a=”223”,那开销可想而知,而JDK的开发者自然想到了这点,采用了享元模式解决创建大量相同String变量带来的开销问题

总结

享元模式，其功能是在运行时减少实例的个数，节省内存。当一个类有许多的实例，而这些实例能被统一个方法控制到时候，可以用享元模式。