layout: pattern

title: Collection Pipeline

folder: collection-pipeline

permalink: /patterns/collection-pipeline/

categories: Functional

tags:

- Java

- Difficulty-Beginner

- Functional

Collection Pipeline introduces Function Composition and Collection Pipeline, two functional-style patterns that you can combine to iterate collections in your code.

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.


Use the Collection Pipeline pattern when

* When you want to perform a sequence of operations where one operation's collected output is fed into the next

* When you use a lot of statements in your code

* When you use a lot of loops in your code

* [Function composition and the Collection Pipeline pattern](https://www.ibm.com/developerworks/library/j-java8idioms2/index.html)

* [Martin Fowler](https://martinfowler.com/articles/collection-pipeline/)

* [Java8 Streams](https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html)

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<class id="1" language="java" name="com.iluwatar.collectionpipeline.App" project="collection-pipeline"

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<operations public="true" package="true" protected="true" private="true" static="true"/>

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</class>

<class id="2" language="java" name="com.iluwatar.collectionpipeline.ImperativeProgramming"

project="collection-pipeline"

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<operations public="true" package="true" protected="true" private="true" static="true"/>

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</class>

<class id="3" language="java" name="com.iluwatar.collectionpipeline.Car" project="collection-pipeline"

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<operations public="true" package="true" protected="true" private="true" static="true"/>

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</class>

<class id="4" language="java" name="com.iluwatar.collectionpipeline.CarFactory" project="collection-pipeline"

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<operations public="true" package="true" protected="true" private="true" static="true"/>

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<class id="5" language="java" name="com.iluwatar.collectionpipeline.FunctionalProgramming"

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<operations public="true" package="true" protected="true" private="true" static="true"/>

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</class>

<enumeration id="6" language="java" name="com.iluwatar.collectionpipeline.Category" project="collection-pipeline"

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<class id="7" language="java" name="com.iluwatar.collectionpipeline.Person" project="collection-pipeline"

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<dependencies>

<dependency>

<groupId>org.junit.jupiter</groupId>

<artifactId>junit-jupiter-api</artifactId>

<scope>test</scope>

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<dependency>

<groupId>org.junit.jupiter</groupId>

<artifactId>junit-jupiter-engine</artifactId>

<scope>test</scope>

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</project>

package com.iluwatar.collectionpipeline;

import java.util.Arrays;

import java.util.List;

import java.util.Map;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

public class App {

private static final Logger LOGGER = LoggerFactory.getLogger(App.class);

/**

public static void main(String[] args) {

List<Car> cars = CarFactory.createCars();

List<String> modelsImperative = ImperativeProgramming.getModelsAfter2000(cars);

LOGGER.info(modelsImperative.toString());

List<String> modelsFunctional = FunctionalProgramming.getModelsAfter2000(cars);

LOGGER.info(modelsFunctional.toString());

Map<Category, List<Car>> groupingByCategoryImperative = ImperativeProgramming.getGroupingOfCarsByCategory(cars);

LOGGER.info(groupingByCategoryImperative.toString());

Map<Category, List<Car>> groupingByCategoryFunctional = FunctionalProgramming.getGroupingOfCarsByCategory(cars);

LOGGER.info(groupingByCategoryFunctional.toString());

Person john = new Person(cars);

List<Car> sedansOwnedImperative = ImperativeProgramming.getSedanCarsOwnedSortedByDate(Arrays.asList(john));

LOGGER.info(sedansOwnedImperative.toString());

List<Car> sedansOwnedFunctional = FunctionalProgramming.getSedanCarsOwnedSortedByDate(Arrays.asList(john));

LOGGER.info(sedansOwnedFunctional.toString());

}

}

package com.iluwatar.collectionpipeline;

public class Car {

private String make;

private String model;

private int year;

private Category category;

/**

public Car(String make, String model, int yearOfMake, Category category) {

this.make = make;

this.model = model;

this.year = yearOfMake;

this.category = category;

}

@Override

public int hashCode() {

final int prime = 31;

int result = 1;

result = prime * result + ((category == null) ? 0 : category.hashCode());

result = prime * result + ((make == null) ? 0 : make.hashCode());

result = prime * result + ((model == null) ? 0 : model.hashCode());

result = prime * result + year;

return result;

}

@Override

public boolean equals(Object obj) {

if (this == obj) {

return true;

}

if (obj == null) {

return false;

}

if (getClass() != obj.getClass()) {

return false;

}

Car other = (Car) obj;

if (category != other.category) {

return false;

}

if (make == null) {

if (other.make != null) {

return false;

}

} else if (!make.equals(other.make)) {

return false;

}

if (model == null) {

if (other.model != null) {

return false;

}

} else if (!model.equals(other.model)) {

return false;

}

if (year != other.year) {

return false;

}

return true;

}

public String getMake() {

return make;

}

public String getModel() {

return model;

}

public int getYear() {

return year;

}

public Category getCategory() {

return category;

}

}