Added setBalance setter and buyProduct core logic

src/User.java

@@ -14,4 +14,8 @@ public class User {
     public int getBalance() {
         return balance;
     }
+
+    public void setBalance(int balance) {
+        this.balance = balance;
+    }
 }

src/UserManager.java

@@ -16,18 +16,19 @@ public class UserManager {
         productList.add(new ProductCard("Шуба", 23000, 10));
 
 
-        System.out.println("Товар: " + productList.get(0).getTitle() + " цена со скидкой " + productList.get(0).getFinalPrice());
+        buyProduct(userList.get(0), productList.get(0));
-        System.out.println("Товар: " + productList.get(1).getTitle() + " цена со скидкой " + productList.get(1).getFinalPrice());
+        buyProduct(userList.get(0), productList.get(1));
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     }
+
+    public void buyProduct (User user, ProductCard product) {
+        int finalPrice = product.getFinalPrice();
+
+        if (user.getBalance() >= finalPrice) {
+            int newBalance = user.getBalance() - finalPrice;
+            user.setBalance(newBalance);
+            System.out.println(" Пользователь " + user.getName() + " успешно купил " + product.getTitle() + " за " + finalPrice);
+            System.out.println(" Остаток на балансе " + user.getBalance());
+        }
+    }
 }