import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.Comparator;
import java.util.Arrays;
import java.util.stream.Collectors;
class Main {
public static void main(String[] args) {
List<Item> items = Arrays.asList(
new Item("A", "X", 100.0),
new Item("B", "X", 30.0),
new Item("C", "X", 80.0),
new Item("D", "Y", 60.0),
new Item("E", "Y", 40.0)
);
// Expected: {X=[100.0, 80.0], Y=[60.0]}
Map<String, List<Double>> itemExpensiveItemsByCategory = expensiveItemsByCategory(items);
System.out.println(itemExpensiveItemsByCategory);
}
/**
* Map<String, List<Double>> where key is category, value is list of prices over 50, sorted descending
*/
public static Map<String, List<Double>> expensiveItemsByCategory(List<Item> items) {
return items.stream()
.collect(Collectors.groupingBy(Item::getCategory, TreeMap::new, Collectors.filtering(
item -> item.getPrice() > 50.0,
Collectors.mapping(
item -> item.getPrice(),
Collectors.collectingAndThen(
Collectors.toList(),
list -> {
list.sort(Comparator.reverseOrder());
return list;
}
)
)) )
);
}
}
class Item {
private String name;
private String category;
private double price;
public Item(String name, String category, double price) {
this.name = name;
this.category = category;
this.price = price;
}
public String getName() { return name; }
public String getCategory() { return category; }
public double getPrice() { return price; }
}
