Intent: A fluent interface provides an easy-readable, flowing interface, that often mimics a domain specific language. Using this pattern results in code that can be read nearly as human language.

Implementation:

A fluent interface can be implemented using any of

• Method Chaining - calling a method returns some object on which further methods can be called.
• Static Factory Methods and Imports
• Named parameters - can be simulated in Java using static factory methods.

Applicability: Use the Fluent Interface pattern when

• you provide an API that would benefit from a DSL-like usage
• you have objects that are difficult to configure or use

Real world examples:

• Java 8 Stream API
• Google Guava FluentInterable
• JOOQ
• Mockito
• Java Hamcrest

Credits

• Fluent Interface - Martin Fowler
• Evolutionary architecture and emergent design: Fluent interfaces - Neal Ford
• Internal DSL