设计模式-享元模式

享元模式

定义

享元模式（Flyweight Pattern）主要用于减少创建对象的数量，以减少内存占用和提高性能。它提供了减少对象数量从而改善应用所需的对象结构的方式。

享元模式尝试重用现有的同类对象，如果未找到匹配的对象，则创建新对象。

类图

Flyweight（轻量级）

按照通常方式编写程序会导致程序变重，所以如果能够共享示例会比较好，而Flyweight表示的就是那些实例会被共享的类。

FlyweightFactory（轻量级工厂）

FlyweightFactory是生成Flyweight的工厂，在工厂中生成Flyweight可以实现共享实例

Client（请求者）

使用FlyweightFactory来生成Flyweight。

示例

类图

BigChar

public class BigChar {
    private char charname;
    private String fontdata;
    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 + "?";
        }
    }
    public void print() {
        System.out.print(fontdata);
    }
}

BigCharFactory

public class BigCharFactory {
    private HashMap pool = new HashMap();
    private static BigCharFactory singleton = new BigCharFactory();
    private BigCharFactory() {
    }
    public static BigCharFactory getInstance() {
        return singleton;
    }
    public synchronized BigChar getBigChar(char charname) {
        BigChar bc = (BigChar)pool.get("" + charname);
        if (bc == null) {
            bc = new BigChar(charname); 
            pool.put("" + charname, bc);
        }
        return bc;
    }
}

BigString

public class BigString {
    private BigChar[] bigchars;
    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));
        }
    }
    public void print() {
        for (int i = 0; i < bigchars.length; i++) {
            bigchars[i].print();
        }
    }
}

Main

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]);
        bs.print();
    }
}

big-.txt

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

big0.txt

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

big1.txt

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

big2.txt

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

big3.txt

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

big4.txt

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

big5.txt

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

big6.txt

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

big7.txt

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

big8.txt

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

big9.txt

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