Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy This PDF is exclusively for your use in accordance with the Safari Terms of. Head First Design Patterns - U-Cursos J2EE Design Patterns. Head First Java covers a huge amount of practical matters that other texts leave as the “ Kathy. Praise for Head First Design Patterns. “I received the book yesterday and started to read it on the way home and I couldn't stop. I took it to the gym and I expect.

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What's so special about design patterns? At any given moment, someone struggles with the same software design problems you have. And, chances are. Automatically exported from bestthing.info - dieforfree/ edsebooks. Pattern Wranglers: Eric Freeman, Elisabeth Robson In other words, if you use anything in Head First Design Patterns to, say, run a nuclear.

What are we doing? Time to QA that Undo button! Every remote needs a Party Mode! Using a macro command The Command Pattern means lots of command classes Do we really need all these command classes? Simplifying the Remote Control with lambda expressions Simplifying even more with method references What if we need to do more than one thing in our lambda expression? Test the remote control with lambda expressions Check out the results of all those lambda expression commands More uses of the Command Pattern: The Adapter and Facade Patterns: Being Adaptive Adapters all around us Object-oriented adapters If it walks like a duck and quacks like a duck, then it must might be a duck turkey wrapped with a duck adapter The Template Method Pattern: Sir, may I abstract your Coffee, Tea?

Taking the design further Abstracting prepareRecipe What have we done? What did the Template Method get us? What is compareTo? The Iterator and Composite Patterns: Well-Managed Collections Breaking News: Can we encapsulate the iteration? What have we done so far?

What we have so far Making some improvements Cleaning things up with java. Iterator We are almost there What does this get us? What did we do?

We decoupled the Waitress Iterators and Collections Is the Waitress ready for prime time? Just when we thought it was safe What do we need?

Head First Design Patterns pdf – O’Reilly

Now for the test drive Getting ready for a test drive Tools for your Design Toolbox The State Pattern: Sanity check We almost forgot! The Proxy Pattern: Now for the GumballMonitor client Step two: Compound Patterns: Patterns of Patterns Working together Duck reunion What did we do?

Meet the Model-View-Controller A closer look And now for a test run Putting Model 2 to the test Better Living with Patterns: You know you need a pattern when Refactoring time is Patterns time! Module Pattern Variations Import mixins This variation of the pattern demonstrates how globals e.

This effectively allows us to import them and locally alias them as we wish. This takes as its first argument a dot-separated string such as myObj. Using setObject allows us to set the value of children, creating any of the intermediate objects in the rest of the path passed if they don't already exist. For example, if we wanted to declare basket.

Here, we see an example of how to define a namespace which can then be populated with a module containing both a private and public API.

The following example is heavily based on the original YUI Module pattern implementation by Eric Miraglia, but again, isn't vastly different from the vanilla JavaScript version: Y.

Ben Cherry previously suggested an implementation where a function wrapper is used around module definitions in the event of there being a number of commonalities between modules. In the following example, a library function is defined which declares a new library and automatically binds up the init function to document.

For starters, it's a lot cleaner for developers coming from an object-oriented background than the idea of true encapsulation, at least from a JavaScript perspective. Secondly, it supports private data - so, in the Module pattern, public parts of our code are able to touch the private parts, however the outside world is unable to touch the class's private parts no laughing! Oh, and thanks to David Engfer for the joke.

Disadvantages The disadvantages of the Module pattern are that as we access both public and private members differently, when we wish to change visibility, we actually have to make changes to each place the member was used.

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We also can't access private members in methods that are added to the object at a later point. That said, in many cases the Module pattern is still quite useful and when used correctly, certainly has the potential to improve the structure of our application.

Other disadvantages include the inability to create automated unit tests for private members and additional complexity when bugs require hot fixes. It's simply not possible to patch privates.

Instead, one must override all public methods which interact with the buggy privates.

Developers can't easily extend privates either, so it's worth remembering privates are not as flexible as they may initially appear. For further reading on the Module pattern, see Ben Cherry's excellent in-depth article on it. The Revealing Module pattern came about as Heilmann was frustrated with the fact that he had to repeat the name of the main object when we wanted to call one public method from another or access public variables.

The result of his efforts was an updated pattern where we would simply define all of our functions and variables in the private scope and return an anonymous object with pointers to the private functionality we wished to reveal as public.

It also makes it more clear at the end of the module which of our functions and variables may be accessed publicly which eases readability. Disadvantages A disadvantage of this pattern is that if a private function refers to a public function, that public function can't be overridden if a patch is necessary. This is because the private function will continue to refer to the private implementation and the pattern doesn't apply to public members, only to functions. Public object members which refer to private variables are also subject to the no-patch rule notes above.

As a result of this, modules created with the Revealing Module pattern may be more fragile than those created with the original Module pattern, so care should be taken during usage. The Singleton Pattern The Singleton pattern is thus known because it restricts instantiation of a class to a single object. Classically, the Singleton pattern can be implemented by creating a class with a method that creates a new instance of the class if one doesn't exist.

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In the event of an instance already existing, it simply returns a reference to that object. Singletons differ from static classes or objects as we can delay their initialization, generally because they require some information that may not be available during initialization time. They don't provide a way for code that is unaware of a previous reference to them to easily retrieve them. This is because it is neither the object or "class" that's returned by a Singleton, it's a structure.

Think of how closured variables aren't actually closures - the function scope that provides the closure is the closure. In JavaScript, Singletons serve as a shared resource namespace which isolate implementation code from the global namespace so as to provide a single point of access for functions.

What makes the Singleton is the global access to the instance generally through MySingleton. This is however possible in JavaScript. In the GoF book, the applicability of the Singleton pattern is described as follows: There must be exactly one instance of a class, and it must be accessible to clients from a well-known access point. When the sole instance should be extensible by subclassing, and clients should be able to use an extended instance without modifying their code.

The second of these points refers to a case where we might need code such as: mySingleton. FooSingleton above would be a subclass of BasicSingleton and implement the same interface. Why is deferring execution considered important for a Singleton?

It is important to note the difference between a static instance of a class object and a Singleton: whilst a Singleton can be implemented as a static instance, it can also be constructed lazily, without the need for resources nor memory until this is actually needed.

If we have a static object that can be initialized directly, we need to ensure the code is always executed in the same order e. Both Singletons and static objects are useful but they shouldn't be overused - the same way in which we shouldn't overuse other patterns.

In practice, the Singleton pattern is useful when exactly one object is needed to coordinate others across a system. They're often an indication that modules in a system are either tightly coupled or that logic is overly spread across multiple parts of a codebase.

Singletons can be more difficult to test due to issues ranging from hidden dependencies, the difficulty in creating multiple instances, difficulty in stubbing dependencies and so on. Miller Medeiros has previously recommended this excellent article on the Singleton and its various issues for further reading as well as the comments to this article, discussing how Singletons can increase tight coupling. I'm happy to second these recommendations as both pieces raise many important points about this pattern that are also worth noting.

The Observer Pattern The Observer is a design pattern where an object known as a subject maintains a list of objects depending on it observers , automatically notifying them of any changes to state.

When a subject needs to notify observers about something interesting happening, it broadcasts a notification to the observers which can include specific data related to the topic of the notification. When we no longer wish for a particular observer to be notified of changes by the subject they are registered with, the subject can remove them from the list of observers.

It's often useful to refer back to published definitions of design patterns that are language agnostic to get a broader sense of their usage and advantages over time. The definition of the Observer pattern provided in the GoF book, Design Patterns: Elements of Reusable Object-Oriented Software, is: "One or more observers are interested in the state of a subject and register their interest with the subject by attaching themselves. When something changes in our subject that the observer may be interested in, a notify message is sent which calls the update method in each observer.

When the observer is no longer interested in the subject's state, they can simply detach themselves.With this pattern, only a public API is returned, keeping everything else within the closure private.

Head First Design Patterns manages to mix fun, belly-laughs, insight, technical.

What would you do if you were Joe? The Proxy Pattern: Nah, we're all adults here, we can take it. Can we encapsulate the iteration? Filling pages with rah-rah pattern talk, and then tacking this critical guidance on at the end of the book is downright irresponsible. As they aren't exposed to the rest of the page only our exported API is , they're considered truly private.

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