《图解设计模式》笔记（九）避免浪费

二十、Flyweight模式：共享对象，避免浪费

如果都用new来创建对象，将消耗大量内存。

Flyweight模式：通过尽量共享实例来避免new出实例

尽量共用已经存在的实例，这就是Flyweight模式的核心内容。

示例中，这样拼出来的叫“大型字符”

示例程序类图

big0.txt

对应的还有big1.txt至big9.txt，以及big-.txt

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

BigChar

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("big" + charname + ".txt"));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

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。这里是本模式的核心方法public synchronized BigChar getBigChar(char charname) {// 首先会通过pool.get()方法查找，是否存在接收到的字符(charname)所对应的BigChar类的实例。BigChar bc = (BigChar)pool.get("" + charname);if (bc == null) {// 若为null,则目前还没有创建该实例，于是通过new BigChar(charname);来生成实例，bc = new BigChar