How to check if is null and if has a specific value using Optional in java?

Question

Assume that I have this code in my project:

public List<T> getAll(Integer parameter) {
    if(parameter != null && parameter > -1) {
        // do something here
    }
}

My question is: how can I do the checking with Optional instead of using if, or if there is another thing I could use?

Answer 1

Optional's design was inspired by monads known from the world of Functional Programming. In such case, it could look like this:

public List<T> getAll(Integer parameter) {

    return Optional.ofNullable(parameter)
      .filter(p -> p > -1)
      .map(p -> *some modification*) //this line is optional
      .orElseGet(() -> *some default value, probably an empty list*)
}

In such case, condition checking is performed in the filter method. If a given Predicate is not matched, the underlying Optional will be empty.

If you want to perform an operation on the underlying value, use map method by providing it with a Function that should be applied to the element wrapped by the Optional.

At the end, you can simply perform some action using ifPresent(), thrown an exception orElseThrow or simply return a default value with orElse or orElseGet. Keep in mind that orElseGet accepts a Supplier instance which makes it evaluate the default value lazily.

If you want to dig deeper, check out @stuart-marks talk from Devoxx: https://www.youtube.com/watch?v=Ej0sss6cq14&t=2767s

In your case, there might be no need for an Optional at all. Just two methods. One with the parameter and the other without.

Answer 2

You should not use Optional for such a case

As Stuart Marks states in Optional - The Mother of All Bikesheds:

Rule #4: It's generally a bad idea to create an Optional for the specific purpose of chaining methods from it to get a value.

This creates a useless overhead without any improvement for code readability and maintainability. You should thus not wrap your parameter into an optional.

and

Rule #6: Avoid using Optional in fields, method parameters and collections.

Avoid using Optional in method parameters

• it doesn't really work for making parameters optional

• forces call sites to create Optionals for everything:

  myMethod(Optional.of("some value"));

  myMethod(Optional.empty());

See also Why should Java 8's Optional not be used in arguments.