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iluwatar#564: Collection Pipeline pattern
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‎collection-pipeline/README.md

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---
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layout: pattern
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title: Collection Pipeline
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folder: collection-pipeline
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permalink: /patterns/collection-pipeline/
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categories: Functional
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tags:
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- Java
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- Difficulty-Beginner
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- Functional
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---
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## Intent
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Collection Pipeline introduces Function Composition and Collection Pipeline, two functional-style patterns that you can combine to iterate collections in your code.
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In functional programming, it's common to sequence complex operations through a series of smaller modular functions or operations. The series is called a composition of functions, or a function composition. When a collection of data flows through a function composition, it becomes a collection pipeline. Function Composition and Collection Pipeline are two design patterns frequently used in functional-style programming.
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![alt text](./etc/collection-pipeline.png "Collection Pipeline")
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## Applicability
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Use the Collection Pipeline pattern when
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* When you want to perform a sequence of operations where one operation's collected output is fed into the next
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* When you use a lot of statements in your code
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* When you use a lot of loops in your code
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## Credits
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* [Function composition and the Collection Pipeline pattern](https://www.ibm.com/developerworks/library/j-java8idioms2/index.html)
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* [Martin Fowler](https://martinfowler.com/articles/collection-pipeline/)

‎collection-pipeline/etc/collection-pipeline.png

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‎collection-pipeline/etc/collection-pipeline.ucls

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<?xml version="1.0" encoding="UTF-8"?>
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<class-diagram version="1.2.2" icons="true" always-add-relationships="false" generalizations="true" realizations="true"
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associations="true" dependencies="false" nesting-relationships="true" router="FAN">
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<class id="1" language="java" name="com.iluwatar.collectionpipeline.App" project="collection-pipeline"
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file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/App.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="952" y="278"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="2" language="java" name="com.iluwatar.collectionpipeline.ImperativeProgramming"
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project="collection-pipeline"
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file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/ImperativeProgramming.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="552" y="107"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="3" language="java" name="com.iluwatar.collectionpipeline.Car" project="collection-pipeline"
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file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Car.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="476" y="301"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="4" language="java" name="com.iluwatar.collectionpipeline.FunctionalProgramming"
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project="collection-pipeline"
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file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/FunctionalProgramming.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="914" y="105"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="5" language="java" name="com.iluwatar.collectionpipeline.Iterating" project="collection-pipeline"
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file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Iterating.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="723" y="280"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</classifier-display>
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<association-display labels="true" multiplicity="true"/>
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</class-diagram>

‎collection-pipeline/pom.xml

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<!--
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The MIT License
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Copyright (c) 2014 Ilkka Seppälä
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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THE SOFTWARE.
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-->
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>com.iluwatar</groupId>
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<artifactId>java-design-patterns</artifactId>
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<version>1.20.0-SNAPSHOT</version>
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</parent>
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<artifactId>collection-pipeline</artifactId>
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<dependencies>
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<dependency>
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<groupId>org.junit.jupiter</groupId>
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<artifactId>junit-jupiter-api</artifactId>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.junit.jupiter</groupId>
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<artifactId>junit-jupiter-engine</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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</project>

‎collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/App.java

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/**
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* The MIT License
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* Copyright (c) 2014 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.collectionpipeline;
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import java.util.List;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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/**
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* In imperative-style programming, it is common to use for and while loops for
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* most kinds of data processing. Function composition is a simple technique
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* that lets you sequence modular functions to create more complex operations.
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* When you run data through the sequence, you have a collection pipeline.
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* Together, the Function Composition and Collection Pipeline patterns enable
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* you to create sophisticated programs where data flow from upstream to
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* downstream and is passed through a series of transformations.
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*
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*/
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public class App {
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private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
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/**
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* Program entry point.
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*
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* @param args
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* command line args
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*/
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public static void main(String[] args) {
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List<Car> cars = Iterating.createCars();
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List<String> modelsImperative = ImperativeProgramming.getModelsAfter2000UsingFor(cars);
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LOGGER.info(modelsImperative.toString());
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List<String> modelsFunctional = FunctionalProgramming.getModelsAfter2000UsingPipeline(cars);
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LOGGER.info(modelsFunctional.toString());
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}
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}

‎collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Car.java

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/**
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* The MIT License
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* Copyright (c) 2014 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.collectionpipeline;
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/**
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* A Car class that has the properties of make, model, and year.
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*/
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public class Car {
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private String make;
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private String model;
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private int year;
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/**
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* Constructor to create an instance of car.
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* @param theMake the make of the car
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* @param theModel the model of the car
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* @param yearOfMake the year of built of the car
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*/
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public Car(String theMake, String theModel, int yearOfMake) {
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make = theMake;
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model = theModel;
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year = yearOfMake;
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}
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public String getMake() {
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return make;
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}
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public String getModel() {
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return model;
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}
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public int getYear() {
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return year;
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}
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}

‎collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/FunctionalProgramming.java

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/**
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* The MIT License
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* Copyright (c) 2014 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.collectionpipeline;
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import java.util.Comparator;
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import java.util.List;
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import java.util.stream.Collectors;
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/**
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* Iterating and sorting with a collection pipeline
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*
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* <p>In functional programming, it's common to sequence complex operations through
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* a series of smaller modular functions or operations. The series is called a
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* composition of functions, or a function composition. When a collection of
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* data flows through a function composition, it becomes a collection pipeline.
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* Function Composition and Collection Pipeline are two design patterns
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* frequently used in functional-style programming.
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*
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* <p>Instead of passing a lambda expression to the map method, we passed the
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* method reference Car::getModel. Likewise, instead of passing the lambda
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* expression car -> car.getYear() to the comparing method, we passed the method
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* reference Car::getYear. Method references are short, concise, and expressive.
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* It is best to use them wherever possible.
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*
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*/
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public class FunctionalProgramming {
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private FunctionalProgramming() {
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}
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/**
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* Method to get models using for collection pipeline.
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*
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* @param cars {@link List} of {@link Car} to be used for filtering
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* @return {@link List} of {@link String} representing models built after year 2000
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*/
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public static List<String> getModelsAfter2000UsingPipeline(List<Car> cars) {
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return cars.stream().filter(car -> car.getYear() > 2000)
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.sorted(Comparator.comparing(Car::getYear))
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.map(Car::getModel).collect(Collectors.toList());
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}
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}

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