Table Of Content
As you’ve seen, creating systems using composition gives you a lot more flexibility. So this time it won’t be the Duck classes that will implement the flying and quacking interfaces. We know that not all of the subclasses should have flying or quacking behavior, so inheritance isn’t the right answer. And of course there might be more than one kind of flying behavior even among the ducks that do fly...
Book description
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Learning Domain-Driven Design
It will be available in both paper and digital format. Leave your email address now on the appropriate pattern page, and we’ll notify you as soon as you can place your order. It’s my pleasure to introduce you to the first of our three new women’s patterns for Fall 2018. Which of the following are disadvantages of using subclassing to provide specific Duck behavior? As your team begins to share design ideas and experience in terms of patterns, you will build a community of patterns users. You just applied your first design pattern—the STRATEGY Pattern.
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References to this book
In a way that makes you better at solving software design problems, and better at speaking the language of patterns with others on your team. In this chapter, you’ll learn why (and how) you can exploit the wisdom and lessons learned by other developers who’ve been down the same design problem road and survived the trip. Before we’re done, we’ll look at the use and benefits of design patterns, look at some key OO design principles, and walk through an example of how one pattern works. The best way to use patterns is to load your brain with them and then recognize places in your designs and existing applications where you can apply them. Instead of code reuse, with patterns you get experience reuse.
That’s right, you used the Strategy Pattern to rework the SimUDuck app. Thanks to this pattern, the simulator is ready for any changes those execs might cook up on their next business trip to Maui. To change a duck’s behavior at runtime, just call the duck’s setter method for that behavior. What a shame to have all this dynamic talent built into our ducks and not be using it! Imagine you want to set the duck’s behavior type through a setter method on the duck subclass, rather than by instantiating it in the duck’s constructor. We know that fly() and quack() are the parts of the Duck class that vary across ducks.
At any given moment, somewhere in the world someone struggles with the same software design problems you have. You know you don't want to reinvent the wheel (or worse, a flat tire), so you look to Design Patterns--the lessons learned by those who've faced the same problems. With Design Patterns, you get to take advantage of the best practices and experience of others, so that you can spend your time on...something else. 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".
What would you do if you were Joe?
Joe works for a company that makes a highly successful duck pond simulation game, SimUDuck. The game can show a large variety of duck species swimming and making quacking sounds. The initial designers of the system used standard OO techniques and created one Duck superclass from which all other duck types inherit. You can purchase the Hollywood Trousers sewing pattern starting next Wednesday from our website.
Elisabeth Robson is co-founder of Wickedly Smart, an education company devoted to helping customers gain mastery in web technologies. She's co-author of four bestselling books, Head First Design Patterns, Head First HTML and CSS, Head First HTML5 Programming, and Head First JavaScript Programming. What are some factors that drive change in your applications? You might have a very different list, but here’s a few of ours. When you use a pattern in a description, other developers quickly know precisely the design you have in mind.
I also moved the inseam forward, which in my experience gives trousers a much better fit. Additionally, the legs are cut nice and long, which allows you to hem them to the right length, especially if you plan to wear them with heels. Eric Freeman recently ended nearly a decade as a media company executive, having held the position of CTO of Disney Online & Disney.com at The Walt Disney Company. Eric is now devoting his time to WickedlySmart.com and lives with his wife and young daughter in Austin, TX. He holds a Ph.D. in Computer Science from Yale University.
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When you put two classes together like this you’re using composition. Instead of inheriting their behavior, the ducks get their behavior by being composed with the right behavior object. And we can add new behaviors without modifying any of our existing behavior classes or touching any of the Duck classes that use flying behaviors. This is probably old news to you, but just to make sure we’re all saying the same thing, here’s a simple example of using a polymorphic type—imagine an abstract class Animal, with two concrete implementations, Dog and Cat. That way, the Duck classes won’t need to know any of the implementation details for their own behaviors.
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 pattern. 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.
More recently, she's been a master trainer for Sun Microsystems, teaching Sun's Java instructors how to teach the latest technologies to customers, and a lead developer of several Sun certification exams. Along with her partner Bert Bates, Kathy created the Head First series. She's also the original founder of the Software Development/Jolt Productivity Award-winning javaranch.com, the largest (and friendliest) all-volunteer Java community. Elisabeth Robson is the co-author of several Head First books, including Head First Design Patterns, and is a principal at WickedlySmart, an online learning company for software developers. Character is the abstract class for all the other characters (King, Queen, Knight, and Troll), while WeaponBehavior is an interface that all weapon behaviors implement. So all actual characters and weapons are concrete classes.
What Joe thought was a great use of inheritance for the purpose of reuse hasn’t turned out so well when it comes to maintenance. Take O’Reilly with you and learn anywhere, anytime on your phone and tablet.
We think your time is too important (and too short) to spend it struggling with academic texts. If you've read a Head First book, you know what to expect--a visually rich format designed for the way your brain works. Using the latest research in neurobiology, cognitive science, and learning theory, Head First Design Patterns will load patterns into your brain in a way that sticks.
Not only does that make it easier to communicate with the cook, but it gives the cook less to remember because he’s got all the diner patterns in his head. In other words, if you’ve got some aspect of your code that is changing, say with every new requirement, then you know you’ve got a behavior that needs to be pulled out and separated from all the stuff that doesn’t change. Get Mark Richards’s Software Architecture Patterns ebook to better understand how to design components—and how they should interact. There are also live events, courses curated by job role, and more.
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