Object-oriented design anti-patterns

Revision as of 10:45, 23 September 2009

Object-oriented design anti-patterns describe bad design solutions to common problems. As such, they are essentially the opposite of conventional design patterns.

Many of these anti-patterns are closely related to common design maxims.

The following are common object-oriented design anti-patterns:

Architecture Anti-patterns

• Anemic Domain Model - This anti-pattern occurs when data and behaviour is separated in the domain model.
• BaseBean - This anti-pattern occurs when inheritance for implementation is used; that is a class inherits from another class not because it makes sense semantically but because it wants to use methods defined in the superclass.
• Boat anchor - A piece of software or hardware in the system that serves no useful purpose. WB
• Call super - This anti-pattern occurs when a superclass requires derived classes to call an overridden method.
• Circle-ellipse problem - This anti-pattern occurs when inheritance is not used correctly and the Liskov substitution principle is violated.
• Circular dependency - This anti-pattern occurs when there are two or more modules that depend directly or indirectly on each other.
• Constant interface - This anti-pattern occurs when an interface is used to declare constants but does not contain any methods.
• Cut and paste programming - Code reused by copying source from other locations. Increasing the likelihood of errors and decreases maintainability. WB
• Functional decomposition - Classes that resemble the structure of programs creating using functional languages. WB
• God object - This anti-pattern occurs when an object / class does or knows too much.
• Jumble - This anti-pattern describes a situation where "horizontal and vertical design elements are intermixed". This means that domain specific concepts are mixed with hierarchical concepts. WB
• Object cesspool - This anti-pattern occurs when an object pool is used incorrectly in that the state of objects is not reset when they are returned to the pool.
• Object orgy - This anti-pattern occurs when objects access each other internals directly rather than going through methods.
• Poltergeists - This anti-pattern occurs when temporary objects are used to initialize or call methods on more permanent objects.
• Reinvent the wheel - This occurs when developers reinvent material that already exists. This is the "if you write quicksort ever again you're fired" antipattern. WB
• Sequential coupling - This anti-pattern occurs when a class requires clients to call methods in a particular order.
• Spaghetti code - An adhoc structure that is difficult to extend and maintain. WB
• Stovepipe system - The integration of subsystems in an adhoc manner. WB
• Swiss army knife - An excessively complicating interface in which the designer attempts to provide every conceivable functionality. WB
• The Blob - Equivalent to God object, a very large class with a functional structure. WB
• Vendor lock-in - Occurs in systems that are highly dependent on propitiatory architectures. WB
• Yo-yo problem - This problem occurs with deep inheritance hierarchies, where a programmer has to keep looking up and down the hierarchy to understand the flow of control of the program.

Development & Management Antipatterns

• Continuous obsolescence - When technology changes so rapidly that the development can't keep up with current versions of the software. WB
• Design by committee - This antipattern results in a overtly complex system that lacks coherence. This can occur when the design team does not work together in a cohesive manner. WB
• Golden hammer - When a single technique is applied "obsessively" to software problems. WB
• Lava flow - Dead and forgotten code that hardens and becomes unchanged as the system develops. Requires a change in development strategy. WB
• Mushroom management - This occurs when developers are separated from the end users. WB

See also

• Antipatterns
• Design patterns