Java Coding Problems

249. Returning a boolean if the Optional class is empty

Let's assume that we have the following simple method:

public static Optional<Cart> fetchCart(long userId) {  // the shopping cart of the given "userId" can be null  Cart cart = ...;  return Optional.ofNullable(cart);}

Now, we want to write a method named cartIsEmpty() that calls the fetchCart() method and returns a flag that is true if the fetched cart is empty. Before JDK 11, we could implement this method based on Optional.isPresent(), as follows:

// Avoid (after JDK 11)public static boolean cartIsEmpty(long id) {  Optional<Cart> cart = fetchCart(id);  return !cart.isPresent();}

This solution works fine but is not very expressive. We check for emptiness via presence, and we have to negate ...