• Design pattern – a general reusable solution to a commonly occurring problem
• Best practices in the programming world.
• Often, people only understand how to apply certain software design techniques to certain problems. 
• Can speed OO design

•Patterns can exist at different levels of abstraction

• –At the most concrete level, a class definition with code
• –At the most abstract level, an approach to a problem

•Patterns should contain five main elements

• –Pattern name, problem, solution, example, benefits and consequences

Design Patterns also Known as Gang OF Four design Patterns. Which was designed by 

• Erich Gamma
• Richard Helm
• Ralph Johnson
• John Vlissides

Types of Design Patterns

• Creational - Help assign responsibilities to classes to instantiate new objects
• Behavioral -  Identify and realize common communication patterns between objects
• Structural - Concerned with how classes and objects are composed to form larger structures