delegation Comparison Table

Object Oriented Software Engineering View all facts Glossary Help

subject > pattern > design pattern > delegation

Next design pattern: facade Up: design pattern Previous design pattern: composite

delegation comparison table

Subject have solution have related patterns have context have forces have problem has definition have antipatterns is a subtopic of is a kind of is an instance of

design pattern zero or more related design patterns a context one or more forces a sentence or two explaining the main difficulty being tackled A pattern useful for the design of software zero or more antipatterns - solutions that are inferior or do not work in this context with the reason for their rejection 6.1 - Introduction to Patterns pattern

delegation
Create a method in the ŤDelegatorť class that does only one thing: it calls a method in a neighbouring ŤDelegateť class, allowing reuse of the method for which the ŤDelegateť has responsibility
By 'neighbouring', we mean the ŤDelegateť is connected to the ŤDelegatorť by an association.
Normally, in order to use delegation an association should already exist between the ŤDelegatorť and the ŤDelegateť.
This association needs only to be unidirectional from ŤDelegatorť to ŤDelegateť.
However it may sometimes be appropriate to create a new association just so you can use delegation - provided this does not increase the overall complexity of the system.
Adapter and Proxy patterns
You need an operation in a class and you realize that another class has an implementation of the operation.
However, inheritance is not appropriate, either because the isa rule does not apply, or because you do not want to reuse all the methods of the other class
You want to minimize development cost and complexity by reusing methods
You want to reduce the linkages between classes
You want to ensure that work is done in the most appropriate class
How can you most effectively make use of a method that already exists in the other class? A pattern in which one procedure does nothing more than call another in a neighbouring class; this reduces total coupling in the system
Overusing generalization and inheriting the method that is to be reused
Instead of creating a single method in the ŤDelegatorť that does nothing other than call a method in the ŤDelegateť, you might consider having many different methods in the ŤDelegatorť call the delegate's method? It would be better to ensure that only one method in the ŤDelegatorť calls the method in the ŤDelegateť. If many methods access the method in the ŤDelegateť, then when it changes, you may have to change every method that accesses it
a method must only accesses neighbouring classes
6.7 - The Delegation Pattern design pattern

Subject	have solution	have related patterns	have context	have forces	have problem	has definition	have antipatterns	is a subtopic of	is a kind of	is an instance of
design pattern		zero or more related design patterns	a context	one or more forces	a sentence or two explaining the main difficulty being tackled	A pattern useful for the design of software	zero or more antipatterns - solutions that are inferior or do not work in this context with the reason for their rejection	6.1 - Introduction to Patterns	pattern
delegation	Create a method in the ŤDelegatorť class that does only one thing: it calls a method in a neighbouring ŤDelegateť class, allowing reuse of the method for which the ŤDelegateť has responsibility By 'neighbouring', we mean the ŤDelegateť is connected to the ŤDelegatorť by an association. Normally, in order to use delegation an association should already exist between the ŤDelegatorť and the ŤDelegateť. This association needs only to be unidirectional from ŤDelegatorť to ŤDelegateť. However it may sometimes be appropriate to create a new association just so you can use delegation - provided this does not increase the overall complexity of the system.	Adapter and Proxy patterns	You need an operation in a class and you realize that another class has an implementation of the operation. However, inheritance is not appropriate, either because the isa rule does not apply, or because you do not want to reuse all the methods of the other class	You want to minimize development cost and complexity by reusing methods You want to reduce the linkages between classes You want to ensure that work is done in the most appropriate class	How can you most effectively make use of a method that already exists in the other class?	A pattern in which one procedure does nothing more than call another in a neighbouring class; this reduces total coupling in the system	Overusing generalization and inheriting the method that is to be reused Instead of creating a single method in the ŤDelegatorť that does nothing other than call a method in the ŤDelegateť, you might consider having many different methods in the ŤDelegatorť call the delegate's method? It would be better to ensure that only one method in the ŤDelegatorť calls the method in the ŤDelegateť. If many methods access the method in the ŤDelegateť, then when it changes, you may have to change every method that accesses it a method must only accesses neighbouring classes	6.7 - The Delegation Pattern		design pattern

Next design pattern: facade Up: design pattern Previous design pattern: composite