Java Optional

Automation Testing Interview Help, Java, Selenium WebDriver, Test Automation / March 17, 2021 / 79 Comments

Optional was introduced in Java 8 and its primary objective is to prevent NullPointer exceptions in code.

Consider it as wrapper/container object which may or may not hold a non-null value. One needs to unwrap/de-containerize it to get the actual content using methods provided by Optional itself. For example – method ‘isPresent‘ invoked on Optional instance returns true if it contains a non-null value and method ‘get’ will return the actual content.

Let us try to understand this with below example.

In class ‘UsePersonClass’ we use a zero-argument constructor to create instance of ‘Person’ class (line 17). Thus, member variable of the instance will hold null.

So ‘person.getName()’ on line 20, will return Null. And since we have called ‘toLowerCase’ method on Null object, it throws NullPointer exception.

If we analyse, the reason for this exception are-

  1. In ‘Person’ class we declared return type of ‘getName’ function as String. This does not mandate the consumer of this class (in this example, UsePersonClass is its consumer) to do a check for Null values.
  2. The consumer class, ‘UsePersonClass’ missed to put explicit condition to check value returned by ‘getName()’ before invoking further methods on it.

As is evident, putting a null check condition in above program, should have prevented any exception situation. But in large programs where there are multiple provider/model classes (like the ‘Person’ class in this example) the consumer class (like UsePersonClass’ class in this example), one will require to put null checks at multiple steps, which would make the program bulky and difficult to read.

Now let’s see how Optional helps in improving this situation by modifying the earlier provider and consumer classes.

Highlights of this approach

  1. We have changed the return type of function ‘getName’ in ‘Person’ class, to return ‘Optional’ type rather than ‘String’ type (line 4)
  2. ‘Optional.ofNullable(name) converts the String value to an ‘Optional’ object.
  3. Now ‘UsePersonClass’ class CANNOT directly call ‘toLowerCase’ method as it is not available in ‘Optional’ type. Optional here forces user to first check if a non-null value is returned and only then perform further actions.
  4. There are other methods provided by Optional to verify, extract and process Optional object, in functional programming fashion.

Hence using Optional in Person class, we are hinting its consumer that it may or may not return a null value so the consumer can program accordingly and avoid Null Pointer exception.

Other ways to create instance of Optional

1. Optional<Object> personWrappedIntoOptional = Optional.of(person);

Use this only when you are sure that ‘person’ will not be Null. If there is possibility of ‘person’ to be Null, use Optional.ofNullable

2. Optional<Object> emptyOptional = Optional.empty();

Creates an empty Optional instance.

Illustration of usage of few methods provided by Optional:

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