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Ilkka Seppälä
2020-08-29 21:00:17 +03:00
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@ -9,23 +9,25 @@ tags:
---
## 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.
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.
## Explanation
The Fluent Interface pattern is useful when you want to provide an easy readable, flowing API. Those interfaces tend
to mimic domain specific languages, so they can nearly be read as human languages.
The Fluent Interface pattern is useful when you want to provide an easy readable, flowing API. Those
interfaces tend to mimic domain specific languages, so they can nearly be read as human languages.
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
* 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.
Real world example
> We need to select numbers based on different criteria from the list. It's a great chance to utilize fluent interface pattern to provide readable easy-to-use developer experience.
> We need to select numbers based on different criteria from the list. It's a great chance to
> utilize fluent interface pattern to provide readable easy-to-use developer experience.
In plain words
@ -33,7 +35,9 @@ In plain words
Wikipedia says
> In software engineering, a fluent interface is an object-oriented API whose design relies extensively on method chaining. Its goal is to increase code legibility by creating a domain-specific language (DSL).
> In software engineering, a fluent interface is an object-oriented API whose design relies
> extensively on method chaining. Its goal is to increase code legibility by creating a
> domain-specific language (DSL).
**Programmatic Example**
@ -134,29 +138,35 @@ result is printed afterwards.
.first(2)
.last()
.ifPresent(number -> LOGGER.info("Last amongst first two negatives: {}", number));
// The initial list contains: 1, -61, 14, -22, 18, -87, 6, 64, -82, 26, -98, 97, 45, 23, 2, -68.
// The first three negative values are: -61, -22, -87.
// The last two positive values are: 23, 2.
// The first even number is: 14
// A string-mapped list of negative numbers contains: String[-61], String[-22], String[-87], String[-82], String[-98], String[-68].
// The lazy list contains the last two of the first four positive numbers mapped to Strings: String[18], String[6].
// Last amongst first two negatives: -22
```
Program output:
```java
The initial list contains: 1, -61, 14, -22, 18, -87, 6, 64, -82, 26, -98, 97, 45, 23, 2, -68.
The first three negative values are: -61, -22, -87.
The last two positive values are: 23, 2.
The first even number is: 14
A string-mapped list of negative numbers contains: String[-61], String[-22], String[-87], String[-82], String[-98], String[-68].
The lazy list contains the last two of the first four positive numbers mapped to Strings: String[18], String[6].
Last amongst first two negatives: -22
```
## Class diagram
![Fluent Interface](./etc/fluentinterface.png "Fluent Interface")
## 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
* You provide an API that would benefit from a DSL-like usage.
* You have objects that are difficult to configure or use.
## Known uses
* [Java 8 Stream API](http://www.oracle.com/technetwork/articles/java/ma14-java-se-8-streams-2177646.html)
* [Google Guava FluentInterable](https://github.com/google/guava/wiki/FunctionalExplained)
* [Google Guava FluentIterable](https://github.com/google/guava/wiki/FunctionalExplained)
* [JOOQ](http://www.jooq.org/doc/3.0/manual/getting-started/use-cases/jooq-as-a-standalone-sql-builder/)
* [Mockito](http://mockito.org/)
* [Java Hamcrest](http://code.google.com/p/hamcrest/wiki/Tutorial)