使用 lambda 和流映射列表对象

Question

首先，我有以下发票清单。每个列表对象都有一个部件号、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);

问什么：使用 lambdas 和流来映射PartDescription 和 Quantity 上的每个 Invoice，按 Quantity 排序并显示结果。

所以我现在拥有的：

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

我将它映射到数量上并按数量排序，我得到以下结果：

3
7
11
16
18
21
34
76

但是我如何也映射到PartDescription，以便在我的结果中也显示在显示的数量前面？我不能这样做：

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

Answer 1

你不使用map。您对Invoices 中的原始Stream 进行排序，然后打印您想要的任何属性。

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

编辑：如果您想按数量 * 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()));