建造者模式（Builder）

//: builder:BuildMedia.java
// Example of the Builder pattern
package test;

import java.util.*;
import junit.framework.*;

// Different "representations" of media:
class Media extends ArrayList {
}

class Book extends Media {
}

class Magazine extends Media {
}

class WebSite extends Media {
}

// ... contain different kinds of media items:
class MediaItem {
	private String s;

	public MediaItem(String s) {
		this.s = s;
	}

	public String toString() {
		return s;
	}
}

class Chapter extends MediaItem {
	public Chapter(String s) {
		super(s);
	}
}

class Article extends MediaItem {
	public Article(String s) {
		super(s);
	}
}

class WebItem extends MediaItem {
	public WebItem(String s) {
		super(s);
	}
}

// ... but use the same basic construction steps:
class MediaBuilder {
	public void buildBase() {
	}

	public void addMediaItem(MediaItem item) {
	}

	public Media getFinishedMedia() {
		return null;
	}
}

class BookBuilder extends MediaBuilder {
	private Book b;

	public void buildBase() {
		System.out.println("Building book framework");
		b = new Book();
	}

	public void addMediaItem(MediaItem chapter) {
		System.out.println("Adding chapter " + chapter);
		b.add(chapter);
	}

	public Media getFinishedMedia() {
		return b;
	}
}

class MagazineBuilder extends MediaBuilder {
	private Magazine m;

	public void buildBase() {
		System.out.println("Building magazine framework");
		m = new Magazine();
	}

	public void addMediaItem(MediaItem article) {
		System.out.println("Adding article " + article);
		m.add(article);
	}

	public Media getFinishedMedia() {
		return m;
	}
}

class WebSiteBuilder extends MediaBuilder {
	private WebSite w;

	public void buildBase() {
		System.out.println("Building web site framework");
		w = new WebSite();
	}

	public void addMediaItem(MediaItem webItem) {
		System.out.println("Adding web item " + webItem);
		w.add(webItem);
	}

	public Media getFinishedMedia() {
		return w;
	}
}

class MediaDirector { // a.k.a. "Context"
	private MediaBuilder mb;

	public MediaDirector(MediaBuilder mb) {
		this.mb = mb; // Strategy-ish
	}

	public Media produceMedia(List input) {
		mb.buildBase();
		for (Iterator it = input.iterator(); it.hasNext();)
			mb.addMediaItem((MediaItem) it.next());
		return mb.getFinishedMedia();
	}
};

public class BuildMedia extends TestCase {
	private List input = Arrays.asList(new MediaItem[] {
			new MediaItem("item1"), new MediaItem("item2"),
			new MediaItem("item3"), new MediaItem("item4"), });

	public void testBook() {
		MediaDirector buildBook = new MediaDirector(new BookBuilder());
		Media book = buildBook.produceMedia(input);
		String result = "book: " + book;
		System.out.println(result);
		assertEquals(result, "book: [item1, item2, item3, item4]");
	}

	public void testMagazine() {
		MediaDirector buildMagazine = new MediaDirector(new MagazineBuilder());
		Media magazine = buildMagazine.produceMedia(input);
		String result = "magazine: " + magazine;
		System.out.println(result);
		assertEquals(result, "magazine: [item1, item2, item3, item4]");
	}

	public void testWebSite() {
		MediaDirector buildWebSite = new MediaDirector(new WebSiteBuilder());
		Media webSite = buildWebSite.produceMedia(input);
		String result = "web site: " + webSite;
		System.out.println(result);
		assertEquals(result, "web site: [item1, item2, item3, item4]");
	}

	public static void main(String[] args) {
		junit.textui.TestRunner.run(BuildMedia.class);
	}
} // /:~