程序代碼:
public class FlyweightFactory {
//Flyweight pool
private Hashtable flyweights = new Hashtable();
public Flyweight getFlyweight( Object key ) {
Flyweight flyweight = (Flyweight) flyweights.get(key);
if( flyweight == null ) {
//產生新的ConcreteFlyweight
flyweight = new ConcreteFlyweight();
flyweights.put( key, flyweight );
}
return flyweight;
}
}
至此,Flyweight模式的基本框架已經就緒,我們看看如何調用:
程序代碼:
FlyweightFactory factory = new FlyweightFactory();
Flyweight fly1 = factory.getFlyweight( "Fred" );
Flyweight fly2 = factory.getFlyweight( "Wilma" );
......
從調用上看,好象是個純粹的Factory使用,但奧妙就在於Factory的內部設計上.
Flyweight模式在XML等數據源中應用
我們上麵已經提到,當大量從數據源中讀取字符串,其中肯定有重複的,那麼我們使用Flyweight模式可以提高效率,以唱片CD為例,在一個XML文件中,存放了多個CD的資料.
每個CD有三個字段:
1.出片日期(year)
2.歌唱者姓名等信息(artist)
3.唱片曲目 (title)
其中,歌唱者姓名有可能重複,也就是說,可能有同一個演唱者的多個不同時期 不同曲目的CD.我們將"歌唱者姓名"作為可共享的ConcreteFlyweight.其他兩個字段作為UnsharedConcreteFlyweight.
首先看看數據源XML文件的內容:
程序代碼:
＜?xml version="1.0"?＞
＜collection＞
＜cd＞
＜title＞Another Green World＜/title＞
＜year＞1978＜/year＞
＜artist＞Eno, Brian＜/artist＞
＜/cd＞
＜cd＞
＜title＞Greatest Hits＜/title＞
＜year＞1950＜/year＞
＜artist＞Holiday, Billie＜/artist＞