import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.Arrays;
import java.util.stream.Collectors;
class Main {
public static void main(String[] args) {
List<Item> items = Arrays.asList(
new Item("Mouse", 15.0),
new Item("Keyboard", 25.0),
new Item("Mouse", 30.0),
new Item("Keyboard", 120.0),
new Item("Mouse", 10.0)
);
Map<String, Integer> itemsCountByName = items.stream()
.map(Item::getName)
.collect(Collectors.groupingBy(name -> name, TreeMap::new, Collectors.summingInt(n -> 1)));
itemsCountByName.forEach((k,v) -> System.out.println(k + ": " + v));
Map<String, Double> averagePricePerProduct = items.stream()
.collect(Collectors.groupingBy(Item::getName, TreeMap::new, Collectors.averagingDouble(Item::getPrice)));
averagePricePerProduct.forEach((k,v) -> System.out.println(k + ": " + String.format("%.2f", v)));
Map<String, Double> totalPerCategory = items.stream()
.collect(Collectors.groupingBy(item -> getCategory(item.getPrice()), Collectors.summingDouble(Item::getPrice)));
final String[] categories = {"Cheap", "Moderate", "Expensive"};
for(String category : categories) {
System.out.println(category + ": " + String.format("%.2f", totalPerCategory.get(category)));
}
}
private static String getCategory(double price) {
if (price < 20) {
return "Cheap";
} else if (price >= 20 && price <= 100) {
return "Moderate";
}
return "Expensive";
}
}
public class Item {
private String name;
private double price;
public Item(String name, double price) {
this.name = name;
this.price = price;
}
public String getName(){
return this.name;
}
public double getPrice() {
return this.price;
}
}
