133 lines
4.8 KiB
Java
133 lines
4.8 KiB
Java
/*
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* The MIT License
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* Copyright © 2014-2019 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.ArrayList;
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import java.util.Collections;
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import java.util.Comparator;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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/**
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* Imperative-style programming to iterate over the list and get the names of cars made later than
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* the year 2000. We then sort the models in ascending order by year.
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*
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* <p>As you can see, there's a lot of looping in this code. First, the
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* getModelsAfter2000UsingFor method takes a list of cars as its parameter. It extracts or filters
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* out cars made after the year 2000, putting them into a new list named carsSortedByYear. Next, it
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* sorts that list in ascending order by year-of-make. Finally, it loops through the list
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* carsSortedByYear to get the model names and returns them in a list.
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*
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* <p>This short example demonstrates what I call the effect of statements. While
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* functions and methods in general can be used as expressions, the {@link Collections} sort method
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* doesn't return a result. Because it is used as a statement, it mutates the list given as
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* argument. Both of the for loops also mutate lists as they iterate. Being statements, that's just
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* how these elements work. As a result, the code contains unnecessary garbage variables
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*/
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public class ImperativeProgramming {
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private ImperativeProgramming() {
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}
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/**
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* Method to return the car models built after year 2000 using for loops.
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*
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* @param cars {@link List} of {@link Car} to iterate over
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* @return {@link List} of {@link String} of car 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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List<Car> carsSortedByYear = new ArrayList<>();
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for (Car car : cars) {
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if (car.getYear() > 2000) {
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carsSortedByYear.add(car);
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}
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}
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Collections.sort(carsSortedByYear, new Comparator<Car>() {
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@Override
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public int compare(Car car1, Car car2) {
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return car1.getYear() - car2.getYear();
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}
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});
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List<String> models = new ArrayList<>();
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for (Car car : carsSortedByYear) {
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models.add(car.getModel());
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}
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return models;
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}
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/**
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* Method to group cars by category using for loops.
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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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Map<Category, List<Car>> groupingByCategory = new HashMap<>();
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for (Car car : cars) {
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if (groupingByCategory.containsKey(car.getCategory())) {
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groupingByCategory.get(car.getCategory()).add(car);
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} else {
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List<Car> categoryCars = new ArrayList<>();
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categoryCars.add(car);
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groupingByCategory.put(car.getCategory(), categoryCars);
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}
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}
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return groupingByCategory;
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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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* using for loops.
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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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List<Car> cars = new ArrayList<>();
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for (Person person : persons) {
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cars.addAll(person.getCars());
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}
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List<Car> sedanCars = new ArrayList<>();
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for (Car car : cars) {
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if (Category.SEDAN.equals(car.getCategory())) {
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sedanCars.add(car);
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}
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}
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sedanCars.sort(new Comparator<Car>() {
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@Override
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public int compare(Car o1, Car o2) {
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return o1.getYear() - o2.getYear();
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}
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});
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return sedanCars;
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}
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}
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