Download a Free Chapter 3 The Decorator Pattern Please login to download. Buy the Book About the Book ISBN: 0596007124 Publisher: O'Reilly Media, Inc. Publication Date: November, 2004 Edition: 1st Binding: Paperback Number of Pages: 638

You want to learn about the patterns that matter--why to use them, when to use them, how to use them (and when NOT to use them). But you don't just want to see how patterns look in a book, you want to know how they look "in the wild". In their native environment. In other words, in real world applications. You also want to learn how patterns are used in the Java API, and how to exploit Java's built-in pattern support in your own code. You want to learn the real OO design principles and why everything your boss told you about inheritance might be wrong (and what to do instead). You want to learn how those principles will help the next time you're up a creek without a design paddle pattern.

Most importantly, you want to learn the "secret language" of Design Patterns so that you can hold your own with your co-worker (and impress cocktail party guests) when he casually mentions his stunningly clever use of Command, Facade, Proxy, and Factory in between sips of a martini. You'll easily counter with your deep understanding of why Singleton isn't as simple as it sounds, how the Factory is so often misunderstood, or on the real relationship between Decorator, Facade and Adapter. With Head First Design Patterns, you'll avoid the embarrassment of thinking Decorator is something from the "Trading Spaces" show. Best of all, in a way that won't put you to sleep!

package decorator;
 
import java.util.*;
 
public class Beverage {
	private BeverageType beverageType;
	private List<Condiment> condiments = new ArrayList<Condiment> ();
 
	public Beverage (BeverageType bevType)
	{	this.beverageType = bevType;	}
 
	public void addCondiment(Condiment condi)
	{	this.condiments.add(condi);	}
 
	public double getCost() {
		double cost = this.beverageType.getCost();
		for (Condiment c : condiments)
			cost += c.getCost();
		return cost;
	}
}
 
/************************************************/
class BeverageType {
	private static Map<String, BeverageType> allBeverageTypes =
		new HashMap<String, BeverageType> ();
 
	private String name;
	private double cost;
 
	// Get the name and cost of each condiment from some data source.
	// The data source can be an XML file, text file, or a database, etc.
 
	static {	loadAllBeverageTypes();	}
 
	public static void loadAllBeverageTypes(){
	   	//for (String nameAndCost : nameAndCostDataSourceArray) {
		// get name and cost from data source string
		//	allBeverageTypes.put(name, newBeverageType(name, cost));
		}
 
	private BeverageType(String name, double cost)
	{	this.cost = cost; this.name = name;	}
 
	public static BeverageType getBeverageType(String bevType)
	{	return allBeverageTypes.get(bevType);
		// Exception handling omitted for simplicity
	}
 
	public double getCost() { return this.cost;	}
}
 
/************************************************/
 
class Condiment {
	// Follows the same pattern as BeverageType.
	private static Map<String, Condiment> allCondiments =
		new HashMap<String, Condiment> ();
 
	private String name;
	private double cost;
 
	// Get the name and cost of each condiment from some data source.
	// The data source can be an XML file, text file, or a database.
 
	static { loadAllCondiments();	}
 
	public static void loadAllCondiments(){
	   	//for (String nameAndCost : nameAndCostDataSourceArray) {
		// get name and cost from data source string
		//	allCondiments.put(name, newCondiment(name, cost));
		//
		// Put all this into a method called loadAllCondiments();
		}
 
	private Condiment(String name, double cost)
	{	this.cost = cost; this.name = name;	}
 
	public static Condiment getCondiment(String condiType)
	{	return allCondiments.get(condiType);
		// Exception handling omitted for simplicity
	}
	public double getCost() { return this.cost;	}
}