Builder Pattern

The Builder pattern is a creational design pattern that provides a flexible solution to the 'telescoping constructor' problem, where the increase of object constructor parameter combination leads to an exponential list of constructors. Instead of using numerous constructors, the builder pattern uses another object, a builder, that receives each initialization parameter step by step and then returns the resulting constructed object at once.

Here is the basic structure of the builder pattern:

1. Product: This is the complex object that is being built.

2. Builder: This is an interface that defines the 'steps' required to build the complex product.

3. ConcreteBuilder: This class implements the Builder interface to construct and assemble the product. It defines and keeps track of the representation it creates. It also provides an interface to retrieve the product.

4. Director: The Director class constructs the complex object using the Builder interface.

A classic example where the Builder pattern is often used is the construction of a complex HTML document or a complex GUI.