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We have looked at the Factory, the Adapter, and the Singleton patterns. Now we look at the Decorator. The Decorator is similar to the Adapter, but with a subtle difference. With our ReptileAdapter, we wrapped the Reptile class to map the interface methods of Animal to the appropriate methods on Reptile. With the Decorator we also wrap a class, but to add functionality, not to map it or replace the functionality.

The Decorator in the Physical World

The idea behind decorating things in the real world is pretty much how it sounds. We wrap an object with new functionality, while keeping the old functionality. How about a camera in a waterproof housing? When closed up, we have added the functionality of waterproofing, but we still provide a way to press the buttons and turn the dials so that the camera can be operated.

The Decorator in the Software World

On the software side, the idea is the same. It is usually used when we have one object that we like how it functions, but we want to augment the behavior for a different situation. Done correctly, we can keep inserting one object inside another adding functionality at every step.
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The last pattern we looked at was the Adapter pattern. It was a good pattern to start with as it maps well to the physical world and is fairly simple. Now we will look at the Singleton pattern. In some respects it is the simplest of patterns, but there are some things to think about.

The Singleton in the Physical World

The idea behind the Singleton is to ensure that there can be only one (insert Highlander jokes here). If you had a factory that made widgets, you would want a widget to be created many many times. But there is only one factory. If you were modeling the US government, you would only want one president. Only one senate.

The Singleton in the Software World

On the software side, the idea is the same. It is usually used when we only want one set of configuration variables, one controller, one data base connection pool, that kind of thing.
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Annotations allow you to attach metadata to a field, class, or method. Metadata is data that describes something else. For example, metadata about a song in mp3 format could be the artists name or the bit rate it was encoded at. A jpeg image could have metadata that described the image height or the number of colors in the image.

What do they look like?

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@Override
public String getName() {
	return "no name";
}

The word after the ‘@’ is the Annotation. It precedes a method or class name. The Override annotation is built into Java. It is used to indicate that a method overrides a parents method. These are used for compiler hinds, for documentation, and to apply meta data.
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To me it seems a better word would be Specifics. The use of Generics is applying a specific type to a class that can be used in a generic way. One of the most common generic classes is List. A list allows you to put any type of Object in to it. In fact, you can put several different types of Objects into a List. But, there is a way to create a specific List type that can only take one type of Object.

What do they look like?

Since we are talking about Lists, lets look at what a ArrayList would look like that could only take Strings.

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List aList = new ArrayList();

What goes between the <> is the type that you want to specify for the List. You need to do it in the left side declaration, and on the right side where you are creating the Object.
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I don’t want to get too deep into every little thing in the collections classes here. In fact, you already know a fair bit about them, because we have used them with some of our Animal class examples. This is more an overview of some of the basic Collections classes.

What do they look like?

There are three main types of collections: Lists, Maps, and Sets. Technically you could try to argue that Map doesn’t extend Collection, so therefore it is not a Collection, but I think of it as part of the group.
They are used for groups of objects, or exactly as its name would imply, collections of objects.

List

A List is just that, a list of objects. The List interface provides a way to add, remove and get objects from a list. It however is just an interface. ArrayList is one of the more popular concrete collections that implements the List interface. Each implementation of the List interface may behave slightly different, but once you understand how a List works, you have a good start on understanding any List.
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I had all kinds of trouble getting Zenphoto to install on 1and1. None of which I believe are the fault of the Zenphoto project. I am blaming the difficulties on how you need to configure php on 1and1.

What problems did I have. It appears that there were tables that were not created correctly. The way I figured this out was that I was trying to save a ¬†guest user and password to¬†and album. The name wouldn’t stick. When I went in and look under the MySql admin¬†tool (phpMyAdmin), there was no user field in the albums table. Something was wrong right from setup.

So here are the steps that I came up with to get zenphoto installed properly. I can’t say that all of the steps I took were necessary, and some might even be suspect, but in total it works.

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In the last lesson we looked at patterns in general and why we might want to use them. So here is our first pattern. We are well on our way to creating a common language with which to talk design.

One of the reasons I picked this pattern to start with, is that it is very easy to understand. It models real word situations very well, and that is what OO design is supposed to do right, model real world objects?

The Adapter in the Physical World

The concept of an Adapter is easy to understand. It does just what it is named to do. It adapts one object to that of another. Take the wall plug. It has three rectangular holes set at angles to fit the plug. It does? In Europe it does. We are traveling and need to plug our laptop into the wall. What do we use? An adapter.

The Adapter in the Software World

The idea is not so different in the software world. When you want to connect one class to another class that was not designed to fit together, you need an adapter class. Let’s look at an Java example to see how we can adapt one class to another.
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Patterns are a very important part of Java. They allow us to speak a common language. The names can be misused, and thrown around by people trying to sound important, but they really do help us to be able to communicate ideas between us.

It does take some Java knowledge to be able to read, use and apply patterns, but I think we have seen enough Java and OO principles to start looking at patterns. It is good to start hearing about and seeing different patterns at any level of Java programming.

So what is a pattern? In the physical world, it would be a series of steps taken over and over again that could be written down and repeated. In the software world, it is not really a set of steps, but a software solution that people apply over and over again in their coding. Experienced developers have put these solutions together, and given their pattern a name. By looking at and studying patterns, we can take advantage of the experience of others, and learn from their solutions. One interesting thing about patterns, is that they don’t need to be language specific. If you learn about the Adapter or the Command pattern, you can apply that pattern to PHP, Ruby, or Java.
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Well, it was pointed out to me that there was an easier way to get RSS feeds onto your site. Feedburner. Guess what. It is also a Google product. Sheesh! Basicly, you need to get your feed registered with Feedburner. Then you can use their BuzzBoost to create a piece of Javascript that will get your feed for you. It is pretty similar to what the GoogleApi is doing that I talked about earlier. The difference here is that Feedburner has a control panel where you set up how  your feed looks. No need to figure out any Javascript at all.

So this is my feed via WordPress.

This is my feed via Feedburner.

This is a snipit of my feed from the BuzzBoost.

Subscribe to RSS headline updates from:
Powered by FeedBurner

And this is the code that was generated that I pasted in. Pretty simple. I had a hard time getting feedburner to recognize my feed, but I am not sure that is feedburners fault. WordPress appears to take a really long time to respond with the feed.

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<script src="http://feeds2.feedburner.com/cyberward?format=sigpro" type="text/javascript" ></script><noscript><p>Subscribe to RSS headline updates from: <a href="http://feeds2.feedburner.com/cyberward"></a><br/>Powered by FeedBurner</p> </noscript>

I set about recently to try to get a RSS feed parsed using only Javascript. Not as easy as I had thought it would be. I had figured that there would be several Javascript library’s around, and I thought for sure that someone would have a jQuery plugin for it. Well, I did find jFeed, but it suffers from a rather large issue. It can’t access sites from a different domain from where it is running. This is really a Javascript security feature. I did a simple AJAX test, and sure enough, Javascript stops us from directly accessing another domain (to prevent cross site scripting attacks).

How do you get around this issue? Well, a php based proxy is one solution. You call via AJAX, this php file that then makes the request to the real feed, and sends it back. That didn’t seem like a simple or elegant enough solution.

I found RssToHtml, which is a PHP script that you can use the parse the RSS feed. Using this, you can even use an server side¬†include to get the feed. This¬†didn’t work on my machine¬†that would only¬†run cgi scripts from the include.¬†

I had just about given up when I stumbled upon the Google AJAX Feed Api. Google to the rescue again.
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