code 39 c# class Component IComponent Decorator in C#.NET

Creator Code 39 in C#.NET Component IComponent Decorator

Component IComponent Decorator
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New with interface Original and new Implementing the interface Aggregate the interface Implement the interface From new to original
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New with original New Implementing the interface Aggregate the interface
Operation routed
From original to new
From new to original
As you can see in the fourth row of the table, variations are found in the clients. For example, the Decorator pattern aggregates the interface so that it can share decorations; it provides the original as a construction parameter. The Bridge-up pattern does the same. To make this more concrete, here are the two statements from the clients:
// Decorator Display(new DecoratorA(new IComponent( )); // Bridge-up Console.WriteLine(new Abstraction(new ImplementationA( )).Operation( ));
The fifth row shows what objects are invoked in the pattern. The Decorator pattern can call the original components or the decorators, but the Bridge pattern variations only call one or the other. The Proxy pattern both aggregates and invokes only the new classes.
Pattern Comparison
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The next row itemizes how the original changes as a result of the pattern. Only the Proxy pattern enables the original to remain completely unchanged. The Decorator pattern relies on there being an interface that everyone implements, which might have to be added after the original classes are developed. The Bridge pattern is more closely coupled, and there is an understanding that the original must incorporate considerable references to the rest of the system. All the patterns rely on rerouting operations. The last row in the table shows that the rerouting is always done from the new code back to the original; in the case of the Bridge pattern, it just depends on which class is called new and which class is called the original. It is worth noting that in real-time applications, where reaction time is important, the overhead of the time for rerouting the operations might not be acceptable.
48 |
2: Structural Patterns: Decorator, Proxy, and Bridge
3
Structural Patterns: Composite and Flyweight
The Composite and Flyweight structural patterns apply to systems that have many data objects. The Composite pattern has wide applicability, and its composite lists can also make use of the Flyweight pattern. The Flyweight pattern shares identical objects behind the scenes to save space. In their implementations, these patterns make use of the following novel C# features: Generics Properties Structs Indexers Implicit typing Initializers Anonymous types
Composite Pattern
Role
The Composite pattern arranges structured hierarchies so that single components and groups of components can be treated in the same way. Typical operations on the components include add, remove, display, find, and group.
Illustration
Computer applications that specialize in grouping data abound these days. Consider a music playlist in iTunes or a digital photo album in Flickr or iPhoto (Figure 3-1). Items are put in a large list, which is then given structure separately.
Looking at the screenshot from iPhoto, we can see that there are different ways of viewing the photos that have been imported: chronologically or by named event. A single photo can appear in many albums ( Last Roll, 2007, and Switzerland, for example). Creating an album forms a composite object but does not entail actually copying the photos. In this context, the important point about the Composite pattern is that the operations carried out on photos and albums of photos should have the same names and effects, even though the implementations are different. For example, the user should be able to display a photo or an album (that contains photos). Similarly, deletions of a single photo or an album should behave in the same way.
Design
The Composite pattern is one of the simplest there is, on the face of it. It has to deal with two types: Components and Composites of those components. Both types agree to conform to an interface of common operations. Composite objects consist of Components, and in most cases, operations on a Composite are implemented by calling the equivalent operations for its Component objects. See Figure 3-2 for the UML diagram for this pattern. The essential players in the Composite pattern UML diagram are:
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