Guidelines for writing processing when a value exists / does not exist in Java Optional

When writing the processing when the value exists / does not exist in Java Optional, the following three methods can be used.

• Optional.isPresent()
• Optional.ifPresent()
• ʻOptional.ifPresentOrElse ()` (Java 9 or later)

I thought about my own guideline as to which method should be used in which case.

Specifications of each method

Optional.isPresent() ʻOptional.isPresent ()is a method that returnstrue if the value exists and false` if it does not. By using it in combination with the if ~ else statement, you can replace the conventional null check syntax almost as it is. However, such usage is also said to be ** "just replacing the null check, there is no point in using Optional" **.

final Optional<String> foo = Optional.ofNullable("foo");

if (foo.isPresent()) {
	System.out.println("foo=" + foo.orElse(""));
} else {
	System.out.println("foo is null");
}

Optional.ifPresent() ʻOptional.ifPresent ()` is a method that executes the function (Consumer) specified by the argument if the value exists. There is a restriction that the processing when the value does not exist cannot be described and ** variables outside the block cannot be rewritten in the function **.

final Optional<String> foo = Optional.ofNullable("foo");

foo.ifPresent(f -> System.out.println("foo=" + f));

Optional.ifPresentOrElse() ʻOptional.ifPresentOrElse ()` executes the first function (Consumer) specified by the argument if the value exists, and executes the second function (Runnable) specified by the argument if it does not exist. The method. You can describe the processing when the value does not exist, but there is a restriction that ** variables outside the block cannot be rewritten in the function **.

final Optional<String> foo = Optional.ofNullable("foo");

foo.ifPresentOrElse(f -> System.out.println("foo=" + f), () -> System.out.println("foo is null"));

flowchart

It is a flowchart of which method should be used in which case.

<!-TODO: Recreate the flowchart with draw.io->

Basically, it seems good to use ʻOptional.ifPresent ()` and use other methods only when you want to rewrite variables outside the block or when you want to describe the processing when the value does not exist.

Reference link

• Optional (Java Platform SE 8 )
• So what if you want to do something like ifNotPresent for an instance of Optional after all?