【Java学习笔记】设计模式20——State（状态）模式

该文章是阅读《图解设计模式》的学习笔记。书本链接https://www.ituring.com.cn/book/1811

Flyweight模式中的“轻量级”是指程序所使用的内存大小，使用内存多的对象就是“重”对象，使用内存少的对象就是“轻”对象。而该模式就是通过尽量共享实例来避免new出新实例。来减轻程序使用的内存大小。下面程序通过通过共享0-9这几个字符串图案来输出一个几位数的字符串。假如需要输出123123这个数字字符串，可以共享使用1、2和3这三个数字字符串图案分别共享使用两次。

0到9的数字字符串图案，文件分别命名为big0.txt到big9.txt：

....######......
..##......##....
..##......##....
..##......##....
..##......##....
..##......##....
....######......
................

......##........
..######........
......##........
......##........
......##........
......##........
..##########....
................

....######......
..##......##....
..........##....
......####......
....##..........
..##............
..##########....
................

....######......
..##......##....
..........##....
......####......
..........##....
..##......##....
....######......
................

........##......
......####......
....##..##......
..##....##......
..##########....
........##......
......######....
................

..##########....
..##............
..##............
..########......
..........##....
..##......##....
....######......
................

....######......
..##......##....
..##............
..########......
..##......##....
..##......##....
....######......
................

..##########....
..##......##....
..........##....
........##......
......##........
......##........
......##........
................

....######......
..##......##....
..##......##....
....######......
..##......##....
..##......##....
....######......
................

....######......
..##......##....
..##......##....
....########....
..........##....
..##......##....
....######......
................

 命名为big-.txt：

................
................
................
................
..##########....
................
................
................

 BigChar类代码：

package com.wen.Flyweight;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class BigChar {
    // 字符名字
    private char charname;
    // 大型字符对应的字符串(由'#' '.' '\n'组成)
    private String fontdata;
    // 构造函数
    public BigChar(char charname) {
        this.charname = charname;
        try {
            BufferedReader reader = new BufferedReader(
                new FileReader("src/com/wen/Flyweight/big" + charname + ".txt")
            );//注意路径
            String line;
            StringBuffer buf = new StringBuffer();
            while ((line = reader.readLine()) != null) {
                buf.append(line);
                buf.append("\n");
            }
            reader.close();
            this.fontdata = buf.toString();
        } catch (IOException e) {
            this.fontdata = charname + "?";
        }
    }
    // 显示大型字符
    public void print() {
        System.out.print(fontdata);
    }
}

 BigCharFactory类代码：

package com.wen.Flyweight;

import java.util.HashMap;

public class BigCharFactory {
    // 管理已经生成的BigChar的实例
    private HashMap pool = new HashMap();
    // Singleton模式
    private static BigCharFactory singleton = new BigCharFactory();
    // 构造函数
    private BigCharFactory() {
    }
    // 获取唯一的实例
    public static BigCharFactory getInstance() {
        return singleton;
    }
    // 生成（共享）BigChar类的实例
    public synchronized BigChar getBigChar(char charname) {
        BigChar bc = (BigChar)pool.get("" + charname);
        if (bc == null) {
            bc = new BigChar(charname); // 生成BigChar的实例
            pool.put("" + charname, bc);
        }
        return bc;
    }
}

BigString类代码： 

package com.wen.Flyweight;

public class BigString {
    // “大型字符”的数组
    private BigChar[] bigchars;
    // 构造函数
    public BigString(String string) {
        bigchars = new BigChar[string.length()];
        BigCharFactory factory = BigCharFactory.getInstance();
        for (int i = 0; i < bigchars.length; i++) {
            bigchars[i] = factory.getBigChar(string.charAt(i));
        }
    }
    // 显示
    public void print() {
        for (int i = 0; i < bigchars.length; i++) {
            bigchars[i].print();
        }
    }
}

Main程序入口类代码： 

package com.wen.Flyweight;

public class Main {
    public static void main(String[] args) {
//        if (args.length == 0) {
//            System.out.println("Usage: java Main digits");
//            System.out.println("Example: java Main 1212123");
//            System.exit(0);
//        }
//        BigString bs = new BigString(args[0]);
        BigString bs = new BigString("123123");
        bs.print();
    }
}

程序运行结果： 

模式中的角色：

FlyWeight（轻量级）：表示那些实例会被共享的类，共享实例可以让程序变“轻”。如上面代码中的BigChar类。

FlyweightFactory（轻量级工厂）：生成Flyweight角色的工厂，该工厂生产的FlyWeight角色可以实现共享实例。如上面代码中的FlyWeightFactory类。

Client（请求者）：负责使用Flyweight来生成Flyweight角色。如上面代码中的BigString类。