a design pattern is a general reusable solution to a commonly occurring problem within a given context in software design. 1. Singleton - only one instnce of the object. If more than one instance is requested the one that already got initiated will be returned, 2. Factory - returns different type of the same object,based on the methid of init that was called. 3.facade - One class has a method that performs a complex process calling several other classes.