85 lines
3.6 KiB
Java
85 lines
3.6 KiB
Java
/**
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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.Map;
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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> getModelsAfter2000(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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* Method to group cars by category using groupingBy
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*
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* @param cars {@link List} of {@link Car} to be used for grouping
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* @return {@link Map} with category as key and cars belonging to that category as value
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*/
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public static Map<Category, List<Car>> getGroupingOfCarsByCategory(List<Car> cars) {
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return cars.stream().collect(Collectors.groupingBy(Car::getCategory));
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}
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/**
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* Method to get all Sedan cars belonging to a group of persons sorted by year of manufacture
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*
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* @param persons {@link List} of {@link Person} to be used
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* @return {@link List} of {@link Car} to belonging to the group
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*/
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public static List<Car> getSedanCarsOwnedSortedByDate(List<Person> persons) {
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return persons.stream().map(Person::getCars).flatMap(List::stream)
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.filter(car -> Category.SEDAN.equals(car.getCategory()))
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.sorted(Comparator.comparing(Car::getYear)).collect(Collectors.toList());
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}
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}
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