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The observer design pattern is a behavioural pattern listed among the 23 well-known "Gang of Four" design patterns that address recurring design challenges in order to design flexible and reusable object-oriented software, yielding objects that are easier to implement, change, test and reuse. [1]
Listener Pattern Architecture. The Listener Pattern is typically known as Observer Pattern. It is a Behavioral Pattern (aka Publish-Subscribe), which deals with dynamic changes in the state of different objects. Listener Pattern follows a structure where an event listener is registered to event source.
Design Patterns: Elements of Reusable Object-Oriented Software (1994) is a software engineering book describing software design patterns. The book was written by Erich Gamma , Richard Helm , Ralph Johnson , and John Vlissides , with a foreword by Grady Booch .
In software, a data access object (DAO) is a pattern that provides an abstract interface to some type of database or other persistence mechanism. By mapping application calls to the persistence layer, the DAO provides data operations without exposing database details. This isolation supports the single responsibility principle.
The indirection pattern supports low coupling and reuses potential between two elements by assigning the responsibility of mediation between them to an intermediate object. An example of this is the introduction of a controller component for mediation between data (model) and its representation (view) in the model-view-controller pattern.
The mediator [1] design pattern is one of the twenty-three well-known design patterns that describe how to solve recurring design problems to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse.
To favor composition over inheritance is a design principle that gives the design higher flexibility. It is more natural to build business-domain classes out of various components than trying to find commonality between them and creating a family tree.
The flyweight pattern is one of twenty-three well-known GoF design patterns. [1] These patterns promote flexible object-oriented software design, which is easier to implement, change, test, and reuse. In other contexts, the idea of sharing data structures is called hash consing.