基于内部列表中的字段对Java中的两个嵌套列表进行排序和分组

Question

这里是 Java 8。我有以下课程：

@Getter
@Setter
public class InventoryItem {

  // For all instances inside the same manufacturer, this value will be the same
  private String manufacturer;
  private String model;
  private BigDecimal price;

}

public class Inventory extends ArrayList<InventoryItem> {
}

public class InventoryProcessor {

  public void processInventoriesForAllManufacturers() {

    // Essentially get a List<List<InventoryItem>>, where in the
    // inner list is a list of all InventoryItems for a particular
    // manufacturer, and the outer list is a list of all manufacturer's
    // inventories
    List<Inventory> inventoriesForAllManufacturers =
      inventoryService.getAllInventories();

    // Now I need to sort this list based on manufacturer name, but how???

  }

}

所以这里的问题是，inventoryService.getAllInventories() 可能会返回相当于：

public List<Inventory> getAllInventories() {

  List<Inventory> allInventories = new ArrayList<>();

  List<InventoryItem> manufacturer1Inv = new ArrayList<InventoryItem>();
  InventoryItem item1 = new InventoryItem(
    "Lorem Ipsum Inc", "FK10", BigDecimal.valueOf(1.99));
  InventoryItem item2 = new InventoryItem(
    "Lorem Ipsum Inc", "FK11", BigDecimal.valueOf(9.99));
  manufacturer1Inv.add(item1);
  manufacturer1Inv.add(item2);

  List<InventoryItem> manufacturer2Inv = new ArrayList<InventoryItem>();
  InventoryItem item3 = new InventoryItem(
    "Ice Station Zebra Associates", "00djd94", BigDecimal.valueOf(12.99));
  InventoryItem item4 = new InventoryItem(
    "Ice Station Zebra Associates", "00djd95", BigDecimal.valueOf(22.99));
  List<InventoryItem> manufacturer2Inv = new ArrayList<InventoryItem>();
  manufacturer2Inv.add(item3);
  manufacturer2Inv.add(item4);

  List<InventoryItem> manufacturer3Inv = new ArrayList<InventoryItem>();
  InventoryItem item5 = new InventoryItem(
    "ACME Corp", "1234A", BigDecimal.valueOf(2.99));
  InventoryItem item6 = new InventoryItem(
    "ACME Corp", "1234B", BigDecimal.valueOf(6.99));
  List<InventoryItem> manufacturer3Inv = new ArrayList<InventoryItem>();
  manufacturer3Inv.add(item5);
  manufacturer3Inv.add(item6);

  Inventory m1Inv = new Inventory(manufacturer1Inv);
  Inventory m2Inv = new Inventory(manufacturer2Inv);
  Inventory m3Inv = new Inventory(manufacturer3Inv);

  allInventories.add(m1Inv);
  allInventories.add(m2Inv);
  allInventories.add(m3Inv);

  return allInventories;

}

属于同一制造商的所有InventoryItems 将具有完全相同的manufacturer 值。

那么，鉴于这个List<Inventory>，我如何根据内部InventoryItems 的唯一manufacturer 值对其进行排序？

含义，一个包含以下顺序的元素的结果列表（给定上面的示例）：

"ACME Corp", "1234A", BigDecimal.valueOf(2.99));
"ACME Corp", "1234B", BigDecimal.valueOf(6.99));
"Ice Station Zebra Associates", "00djd94", BigDecimal.valueOf(12.99));
"Ice Station Zebra Associates", "00djd95", BigDecimal.valueOf(22.99));
"Lorem Ipsum Inc", "FK10", BigDecimal.valueOf(1.99));
"Lorem Ipsum Inc", "FK11", BigDecimal.valueOf(9.99));

迄今为止我最好的尝试：

  public void processInventoriesForAllManufacturers() {

    // Essentially get a List<List<InventoryItem>>, where in the
    // inner list is a list of all InventoryItems for a particular
    // manufacturer, and the outer list is a list of all manufacturer's
    // inventories
    List<Inventory> inventoriesForAllManufacturers =
      inventoryService.getAllInventories();

    // Now I need to sort this list based on manufacturer name, but how???
    List<Inventory> sorted = inventoriesForAllManufacturers.stream().map(inv ->
        Collections::sort(in)).collect(Collectors.toList());

  }

产生编译器错误“对象不是功能接口。”有什么想法我会出错吗？

同样，它们只需要按制造商名称的字母顺序进行分组+排序；在每个制造商的库存中，它们应按插入列表的顺序出现。

Answer 1

首先，Inventory 不应该扩展 ArrayList。它应该有一个List<InventoryItem>。

按制造商排序应该像

一样简单

list.sort(Comparator.comparing(Inventory::getManufacturer));

你只需要在 Inventory 中有一个 getManufacturer() 方法即可。由于 Inventory 的所有项目都具有相同的制造商，因此您需要从此方法返回第一个项目的制造商。

您当然应该确定库存中没有任何物品是否合法，并决定如何在您的订单中放置此类库存。