Examples with Java's Optional

Optional type from Java helps in representing the case of missing value. It also has some functional style API built into it which enables us to create concise code. In this post we will look at some such examples.

Note: There is another post on Optional which explores some important points to keep in mind while using Optional API. You can find it here.

Example 1

Consider an eCommerce company where Customer-s can have a LoyaltyStatus based on their usage of the company’s services. If we have a method getLoyaltyStatus() which returns Optional<LoyaltyStatus> and we want to print a customer’s loyalty-status, we can do so simply by using get()

public void printStatus() {
    Optional<LoyaltyStatus> loyaltyStatusOptional = getLoyaltyStatus();
    if(loyaltyStatusOptional.isPresent()) {
        System.out.println("Customer’s loyalty status is: " + loyaltyStatusOptional.get());
    } else {
        System.out.println("No loyalty status found for customer.");
    }
}

This is perfectly fine, but if we forget to put the isPresent() check, we might get NoSuchElementException from get(). In fact, we can write the same method concisely by using ifPresentOrElse() and we don’t have to use get().

public void printStatus() {
    getLoyaltyStatus()
     .ifPresentOrElse(loyaltyStatus -> System.out.println("Customer’s loyalty status is: " + loyaltyStatus),
                     () -> System.out.println("No loyalty status found for customer."));
}

Here in this case we are interested in the empty-value case as well, so we used ifPresentOrElse(). But if we are not interested in the empty case, we can use ifPresent().

Note: All source code for this post is present here: https://github.com/balkrishnarawool/optional-examples.

Example 2

There are various promotions going on in the company and these promotions give reward points to the customers based on their loyalty-status. Below is an example of a method that retrieves reward points for a customer.

public int getCustomerLoyaltyStatusPoints() {
    Optional<LoyaltyStatus> loyaltyStatusOptional = getLoyaltyStatus();
    if(loyaltyStatusOptional.isPresent()) {
        LoyaltyStatus loyaltyStatus = loyaltyStatusOptional.get();
        return loyaltyStatus.getPoints();
    }
    return 0;
}

What we are actually doing here is, mapping a customer’s loyalty-status to reward points which can be also be done using map().

public int getCustomerLoyaltyStatusPoints() {
    return getLoyaltyStatus()
      .map(LoyaltyStatus::getPoints)
      .orElse(0);
}

We also see orElse() which is used to get value from Optional object with a default. There is also another method orElseGet(). For the difference between these methods see this post.

Example 3

Free shipping is available to customers with GOLD and PLATINUM loyalty-status. So isFreeShippingAvailable() method can be written as

public boolean isFreeShippingAvailable() {
    Optional<LoyaltyStatus> loyaltyStatusOptional = getLoyaltyStatus();
    if(loyaltyStatusOptional.isPresent()) {
        LoyaltyStatus loyaltyStatus = loyaltyStatusOptional.get();
        return loyaltyStatus.equals(GOLD) || loyaltyStatus.equals(PLATINUM);
    }
    return false;
}

Basically what we are doing here is, applying a condition. This can be easily done by using filter() method

public boolean isFreeShippingAvailable() {
    return getLoyaltyStatus()
      .filter(loyaltyStatus -> loyaltyStatus.equals(GOLD) || loyaltyStatus.equals(PLATINUM))
      .isPresent();
}

Example 4

There are different kinds of discounts available to customers. Customers with different loyalty status may or may not get discounts. This is represented by method getDiscount() in LoyaltyStatus which has return type Optional<Discount>. So retrieveDiscount() can be implemented like this

public Optional<Discount> retrieveDiscount() {
    Optional<LoyaltyStatus> loyaltyStatusOptional = getLoyaltyStatus();
    if(loyaltyStatusOptional.isPresent()) {
        LoyaltyStatus loyaltyStatus = loyaltyStatusOptional.get();
        return loyaltyStatus.getDiscount();
    }
    return Optional.empty();
}

What we see here is that we are actually mapping loyalty status to discount. But if we simply use map() we will get an object of Optional<Optional<Discount>>. So we use flatMap() which gives the right type of object.

public Optional<Discount> retrieveDiscountConcise() {
    return getLoyaltyStatus().flatMap(LoyaltyStatus::getDiscount);
}

Use flatMap() when you have an Optional object and the mapping function returns another Optional object.

Example 5

For this example, consider a class ShippingObject. We can create a ShippingObject instance only when we have length, width and height. But we have methods that may or may not return these. i.e. we have three methods retrieveLength(), retrieveWidth() and retrieveHeight(), all returning Optional<Integer>. For simplicity they have been put into one type DimensionsRetriever. Now we can write createShippingObject() method like this

public static Optional<ShippingObject> createShippingObject(DimensionsRetriever retriever) {
    Optional<Integer> length = retriever.retrieveLength();
    Optional<Integer> width = retriever.retrieveWidth();
    Optional<Integer> height = retriever.retrieveHeight();

    if(length.isPresent() && width.isPresent() && height.isPresent()) {
        return Optional.of(new ShippingObject(length.get(), width.get(), height.get()));
    }
    return Optional.empty();
}

Here we have to map the Optional objects to ShippingObject, but we have three of them. So we will have to chain the map() and flatMap() calls like this

public static Optional<ShippingObject> createShippingObjectConcise(DimensionsRetriever retriever) {
    return retriever.retrieveLength().flatMap(length ->
              retriever.retrieveWidth().flatMap(width ->
                  retriever.retrieveHeight().map(height -> new ShippingObject(length, width, height))));
}

This works for more than three Optional objects as well, we just have to extend the chain.

We have see some commonly occurring use cases with Optional and how we can write them concisely with the Optional API. Hope this is useful.

Note: All source code for this post is present here: https://github.com/balkrishnarawool/optional-examples.