1 /* 2 * Copyright (c) 2013 Oracle and/or its affiliates. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 8 * - Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 11 * - Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * - Neither the name of Oracle nor the names of its 16 * contributors may be used to endorse or promote products derived 17 * from this software without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS 20 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, 21 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR 23 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 24 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 25 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 26 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 27 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 28 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 29 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 /* 33 * This source code is provided to illustrate the usage of a given feature 34 * or technique and has been deliberately simplified. Additional steps 35 * required for a production-quality application, such as security checks, 36 * input validation and proper error handling, might not be present in 37 * this sample code. 38 */ 39 package stream; 40 41 import stream.data.Customer; 42 import stream.data.Product; 43 import java.util.Collection; 44 import java.util.Map; 45 import java.util.Optional; 46 import java.util.function.Function; 47 import static java.util.stream.Collectors.*; 48 import static java.util.Comparator.*; 49 import java.util.stream.Stream; 50 51 /** 52 * This program is demo how to use the conversion operator like toArray, 53 * collect(Collectors.toList()), collect(Collectors.toCollection()) 54 * 55 * @author tyan 56 */ 57 public class Conversion extends DemoHelper { 58 59 /** 60 * Convert products which is most expensive in the same category into an 61 * array 62 * 63 * @param func Function convert Product to T, T could be any type that 64 * Product can convert, like price 65 * @return product array which is in every category, value of T is highest 66 */ 67 68 public static <T extends Comparable<T>> Product[] mostTProductsByCategory( 69 Function<Product, T> func) { 70 //Grouping product by category, only select maximal product by comparing 71 //on func 72 Map<String, Optional<Product>> categoryToProduct = products.stream(). 73 collect(groupingBy(Product::getCategory, 74 maxBy(comparing(func)))); 75 76 return categoryToProduct.values().stream(). 77 //get Product object 78 map(Optional::get). 79 //converting stream to an array 80 toArray(Product[]::new); 81 } 82 83 /** 84 * Convert customers to a distinct countries list 85 * 86 * @param ordered true keep original countries list order false not keep 87 * original countries list order 88 * @return a distinct ordered/unordered countries list for all of customers 89 * by given ordered flag 90 */ 91 public static Collection<String> countries(boolean ordered) { 92 Stream<String> countries = customers.stream().map(Customer::getCountry); 93 if (ordered) { 94 /** 95 * Use distinct() follow with collect(Collectors.toCollection) to 96 * get unique countries linked list. Note this way can generate 97 * target container 98 */ 99 return countries.distinct().collect(toList()); 100 } else { 101 /** 102 * Use collect(Collectors.toSet) to get unique countries list. Note 103 * the difference between this and first one is this way doesn't 104 * guarantee the order 105 */ 106 return countries.collect(toSet()); 107 } 108 } 109 }