使用lambda和流映射列表对象

Question

首先，我有以下发票清单。 每个列表对象都有零件编号，描述，数量和价格。

Invoice[] invoices = new Invoice[8];
invoices[0] = new Invoice("83","Electrische schuurmachine",7,57.98);
invoices[1] = new Invoice("24","Power zaag", 18, 99.99);
invoices[2] = new Invoice("7","Voor Hamer", 11, 21.50);
invoices[3] = new Invoice("77","Hamer", 76, 11.99);
invoices[4] = new Invoice("39","Gras maaier", 3, 79.50);
invoices[5] = new Invoice("68","Schroevendraaier", 16, 6.99);
invoices[6] = new Invoice("56","Decoupeer zaal", 21, 11.00);
invoices[7] = new Invoice("3","Moersleutel", 34, 7.50);

List<Invoice> list = Arrays.asList(invoices);

什么是问道：使用lambda表达式和流对每张发票地图PartDescription和Quantity ，排序Quantity和显示结果。

所以我现在有：

list.stream()
    .map(Invoice::getQuantity)
    .sorted()
    .forEach(System.out::println);

我将其映射到数量上，并对其进行排序，结果如下：

3
7
11
16
18
21
34
76

但是，我如何也映射到PartDescription ，因此结果也显示在所显示数量的前面？ 我不能这样做：

list.stream()
    .map(Invoice::getPartDescription)
    .map(Invoice::getQuantity)
    .sorted()
    .forEach(System.out::println);

Answer 1

您不使用map 。 您对原始的Invoice Stream进行排序，然后打印所需的任何属性。

list.stream()
    .sorted(Comparator.comparing(Invoice::getQuantity))
    .forEach(i -> System.out.println(i.getgetQuantity() + " " + i.getPartDescription()));

编辑：如果要按数量*价格排序：

list.stream()
    .sorted(Comparator.comparing(i -> i.getQuantity() * i.getPrice()))
    .forEach(i -> System.out.println(i.getgetQuantity() *  i.getPrice() + " " + i.getPartDescription()));