Structural
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7 terms
Terms | Definitions |
|---|---|
 Proxy | Proxies are front ends to classes that have sensitive data or slow operations. Proxies, like decorators, forward requests on to another object - the difference is that the proxy relationship is set up at design time and is well known in advance, even though the original class is not an active participator in the relationship. Decorators, on the other hand, can be added dynamically. |
| Bridge | Decouples an abstraction from its implementation, enabling them to vary independently. This pattern is useful, for example, when a new version of software is released that will replace an existing version but the older version must still run for existing clients. |
| Decorator | Provide a way of attaching new state and behavior to an object dynamically. The object does not know it is being decorated, which makes this a useful pattern for evolving systems. A key implementation point is that decorators both inherit the original class (or implement an interface in common with the original class) and contain an instantiation of it. Important point: this pattern is based around new objects being created with their own set of operations. |
| Composite | 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. The Composite pattern looks like an ordinary data structure implementation, but it is more than that because of its ability to manipulate the different types of the elements equally. Used in conjunction with the Decorator, Iterator and Visitor patterns |
| Flyweight | Promotes an efficient way to share common information present in small objects that occur in a system in larger numbers. It helps to reduce storage requirements when many values are duplicated. |
| Adapter | Enables a system to use classes whose interfaces don't quite match its requirements. The important contribution of this pattern is that it promotes programming to interfaces. Two varieties exist: Object adapter: aggregate the adaptee, adding behavior to it Class adapter: implements an interface and inherits a class, overriding adaptee behavior. |
| Facade | Provide different high-level views of subsystems whose details are hidden from users. In general, the operations that might be desirable from a users perspective could be made up of different selections of parts of the subsystem. |
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