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.Comparator; 44 import java.util.List; 45 import java.util.stream.Collectors; 46 47 /** 48 * A demo shows how does Stream's subset works. This demo provides two methods 49 * which is using substream method on Stream to get subset of the elements. Note 50 * we can use substream on sorted stream to get top number elements, but we 51 * can't guarantee the element order if stream is not sorted. 52 * 53 * @author hyan 54 */ 55 public class Subset extends DemoHelper { 56 57 /** 58 * Returns a List that contains numbers order which customer is from state, 59 * also execute action on every returned order element. The number must be a 60 * non-negative digit. 61 * <p> 62 * 63 * @param number integer how many orders are expected to be returned 64 * @param state state that customer of order belong to 65 * @return a list contains top number customers that sorted by comp 66 */ 67 public static List<Order> firstNOrdersFromState(int number, 68 String state) { 69 return customers.stream(). 70 //only take customers from a particular state 71 filter(c -> state.equals(c.getRegion())). 72 //get orders of those customers 73 flatMap(c -> c.getOrders().stream()). 74 //get first number of orders 75 limit(number). 76 //collect to a list 77 collect(Collectors.toList()); 78 } 79 80 /** 81 * Returns a List that contains numbers customer sorted by comp, also 82 * execute action on every returned customer element. The number must be a 83 * non-negative digit. 84 * <p> 85 * 86 * @param number integer how many customers are expected to be returned 87 * @param comp Comparator to compare customer 88 * @return a list contains top number customers that sorted by comp 89 */ 90 public static List<Customer> topNCustomer(int number, 91 Comparator<Customer> comp) { 92 //We keep result in topN, then we can test it 93 return customers.stream() 94 . //sort customers by comp 95 sorted(comp). 96 //get first number of orders 97 limit(number). 98 //collect to a list 99 collect(Collectors.toList()); 100 } 101 }