스트림 problem1

src/main/java/yourssu/order/domain/Order.java

@@ -8,4 +8,8 @@ public class Order {
     public Order(List<OrderItem> items) {
         this.items = items;
     }
+
+    public List<OrderItem> getItems() {
+        return items;
+    }
 }

src/main/java/yourssu/order/domain/OrderItem.java

@@ -10,4 +10,12 @@ public OrderItem(String name, int price, int count) {
         this.price = price;
         this.count = count;
     }
+
+    public int getPrice() {
+        return price;
+    }
+
+    public int getCount() {
+        return count;
+    }
 }

src/main/java/yourssu/order/service/OrderAnalyticsService.java

@@ -1,4 +1,20 @@
 package yourssu.order.service;
 
+import yourssu.user.domain.User;
+
+import java.util.List;
+
 public class OrderAnalyticsService {
+
+
+    public double getAvgPrice(List<User> users) {
+        double avgPrice = users.stream()
+                .flatMap(user -> user.getOrders().stream())
+                .flatMap(order -> order.getItems().stream())
+                .mapToDouble(item -> item.getPrice() * item.getCount())
+                .average()
+                .orElse(0.0);
+
+        return avgPrice;
+    }
 }

src/main/java/yourssu/user/domain/User.java

@@ -1,16 +1,22 @@
 package yourssu.user.domain;
 
 import java.util.List;
+
+import yourssu.order.domain.Order;
+import yourssu.order.domain.OrderItem;
 import yourssu.post.domain.Post;
 
 public class User {
-    private final Long id;
-    private final String name;
-    private final List<Post> posts;
-
-    public User(Long id, String name, List<Post> posts) {
-        this.id = id;
-        this.name = name;
-        this.posts = posts;
+
+    private final List<Order> orders;
+
+
+
+    public User(List<Order> orders) {
+        this.orders = orders;
+    }
+
+    public List<Order> getOrders() {
+        return orders;
     }
 }

src/test/java/yourssu/OrderAnalyticsServiceTest.java

@@ -0,0 +1,44 @@
+package yourssu;
+
+import static org.assertj.core.api.Assertions.*;
+import org.junit.jupiter.api.Test;
+import yourssu.order.domain.Order;
+import yourssu.order.domain.OrderItem;
+import yourssu.order.service.OrderAnalyticsService;
+import yourssu.user.domain.User;
+
+import java.util.List;
+
+public class OrderAnalyticsServiceTest {
+
+    private final OrderAnalyticsService orderAnalyticsService = new OrderAnalyticsService();
+
+    @Test
+    void 평균_주문_금액을_구한다() {
+        // given
+        List<User> users = List.of(
+                new User(List.of(
+                        new Order(List.of(
+                                new OrderItem("A", 1000, 2),
+                                new OrderItem("B", 1500, 1)
+                        )),
+                        new Order(List.of(
+                                new OrderItem("C", 500, 3)
+                        ))
+                )),
+                new User(List.of(
+                        new Order(List.of(
+                                new OrderItem("D", 2000, 1),
+                                new OrderItem("E", 800, 2)
+                        ))
+                ))
+        );
+
+        // when
+        double testAvg = orderAnalyticsService.getAvgPrice(users);
+
+        // then
+
+        assertThat(testAvg).isEqualTo(1720.0);
+    }
+}