Builderpattern

The builder pattern is a creational design pattern that separates the construction of a complex object from its representation, enabling the same construction process to create different representations. It is useful when an object must be created with many optional parts or configurations, and when the construction process should be independent of the parts and their order.

Key participants typically include: the product, which is the complex object being built; the builder, an abstract interface that defines methods for creating parts of the product; the concrete builder, which implements the builder and keeps track of the product being built; the director, which controls the construction sequence; and the client, which requests the construction of a product via the builder. The director often orchestrates the building steps, while the client retrieves the finished product from the builder.

Use cases for the builder pattern include constructing objects with numerous optional parameters, creating different representations of a complex object, and avoiding telescoping constructors or large sets of parameters. It supports immutability by constructing the product internally and exposing a final product once construction completes. It also enables fluent interfaces and method chaining when a concrete builder returns this for each step.

Variants include using a nested or inner builder, common in languages like Java, where the builder is a static nested class. The director is optional; clients may construct a product directly via a builder. The pattern complements other creational approaches and is often contrasted with the telescoping constructor pattern and factory methods.