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.Order; 43 import java.util.Map; 44 import java.util.function.Predicate; 45 import static java.util.stream.Collectors.*; 46 47 /** 48 * A demo shows how does Stream's aggregation works. Demo shows 1. Sum operation 49 * on stream interface 2. Use Stream's count operation as Function output 50 * 51 * @author tyan 52 */ 53 public class Aggregation extends DemoHelper { 54 55 /** 56 * Calculate total product's price. 57 * 58 * @return total product's price 59 */ 60 public static double totalProductPrice() { 61 return products.stream(). 62 //map every product to its price 63 mapToDouble(p -> p.getUnitPrice() * p.getUnitsInStock()). 64 //caculation total price 65 sum(); 66 } 67 68 /** 69 * Get every customer's order count that order meets the predicate<p> 70 * It's possible some customers who don't have any order in given period. 71 * 72 * @param predicate a order predicate 73 * @return map for customer's name and its number of order meets the predicate. 74 */ 75 public static Map<String, Long> customerAndOrderCount( 76 Predicate<Order> predicate) { 77 return customers.stream(). 78 //convert customers into a map that key is customer's name and 79 //value is number of orders which filter by predicate 80 collect(toMap( 81 Customer::getCompanyName, c 82 -> c.getOrders().stream(). 83 //filter orders' stream by given predicate 84 filter(predicate). 85 //get number of order which filter by given predicate 86 count() 87 )); 88 } 89 }