How to solve issue "cannot resolve method collect in optional double"? - stream

Question

I've created tests and now I am struggling with implementation using Stream. Please advise how Stream in methods getOrdersCount() and getOrdersTotalValue() should look like? Right now I get ".collect" in red in both methods with error notes "cannot resolve method collect in optional double". Why and how to fix this?
class ShopTestSuite {
Shop shop = new Shop();
Order order1 = new Order(12.30, LocalDate.of(2020, 12, 12), "marta123");
Order order2 = new Order(67.89, LocalDate.of(2019, 1, 12), "Tomek_K");
Order order3 = new Order(123.90, LocalDate.of(2020, 2, 2), "Sylwia");
Order order4 = new Order(22.90, LocalDate.of(2020, 6, 20), "Sylwia");
#Test
public void shouldReturnOrdersCount() {
// When
Integer result = shop.getOrdersCount();
// Then
assertEquals(4, result);
}
#Test
public void shouldOrdersTotalValue() {
// When
Double result = shop.getOrdersTotalValue();
// Then
assertEquals(146.8, result);
}
#BeforeEach
public void initializeShop () {
shop.addOrder(order1);
shop.addOrder(order2);
shop.addOrder(order3);
shop.addOrder(order4);
}
Shop class:
public class Shop {
private Set<Order> orders = new HashSet<>();
public double getOrdersTotalValue(){
return this.orders
.stream()
.mapToDouble(Order ::getValue).sum()
.collect(Collectors.toSet()) //"cannot resolve method collect in optional double"
}
public int getOrdersCount(){
return this.orders
.stream()
.count()
.collect(Collectors.toSet()); //"cannot resolve method collect in optional double"
}

Answer 1

I suppose you don't nead collect(Collectors.toSet()):
public double getOrdersTotalValue(){
return this.orders
.stream()
.mapToDouble(Order ::getValue).sum();
}
public int getOrdersCount(){
return (int)this.orders
.stream()
.count();
}