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 }