Software Design Patterns Anton Danshin Moscow Institute of Physics and Technology Dolgoprudny

Contents What is it? Why do we use it? Classification Example Criticism Anti-patterns Conclusion 2

What is it? General repeatable solution to a commonly occurring problem in software design Description or template for how to solve a problem that can be used in many different situations 3

Why do we use it? Speed up development process Prevent future problems Ease comunication between developers Make your code better Simplicity is the soul of efficiency. -- Austin Freeman, "The Eye of Osiris" 4

Classification of design patterns Creational: Abstract factory, Builder, Factory method, Prototype, Singleton,... Structural: Adapter, Bridge, Composite, Decorator, Proxy,... Behavioral: Chain of responsibility, Command, Iterator, Mediator, Strategy,... Concurrent 5

Example 1: Singleton Intent: Create a single-instance class Provide a global point of access to it Encapsulate initialization Problems Application needs one, and only one, instance of an object. Lazy initialization and global access are necessary 6

Example 1: Singleton 7

Example 1: Singleton (Java) 8

Criticism Targets the wrong problem Lacks formal foundations Leads to inefficient solutions Do not overuse! 9

Copy and Paste Programming Spaghetti Code Golden Hammer Magic Numbers Hard Code Boat Anchor God Object Anti-Patterns Soft Code Reinventing the Wheel Reinventing the Square Wheel Blind Faith Brute Force Coding Unnecessary comments 10

Conclusion Design pattern is a general solution to a commonly occurring problem in software design Using design patterns makes your code better Design patterns are devided into: Creational Behavioral Structural Concurrent Do NOT OVERUSE design patterns 11

References 1.SourceMaking.com – Software Design Patterns 2.Wikipedia 3.HabraHabr.Ru 12

Thanks for your attention!