When Should I Use Optional.orElseGet() Instead of Optional.orElse()?

Understanding the Difference between Optional.orElse() and Optional.orElseGet()

Optional.orElse() and Optional.orElseGet() are two methods in Java that help in handling Optional, a container object that may or may not contain a value.

Description of orElse()

orElse() takes a value (other) as an argument. If the Optional is present (contains a value), it returns that value. However, if the Optional is empty, it returns the provided value (other).

Description of orElseGet()

orElseGet() also takes an argument, but this time it's a Supplier functional interface. A Supplier takes no arguments and returns a value. Unlike orElse(), orElseGet() will only invoke the Supplier function when the Optional is empty.

When to Use orElseGet()?

The main difference between orElse() and orElseGet() is when the provided argument would result in an expensive operation. If the Optional is not empty, using orElse() will still perform the provided operation even though it's unnecessary. However, orElseGet() avoids this unnecessary operation, only executing it when needed.

Example

Consider the following example:

<code class="java">Optional<String> myString = Optional.empty();

String result1 = myString.orElse(ExpensiveOperation.getExpensiveString()); // ExpensiveOperation always executed
String result2 = myString.orElseGet(() -> ExpensiveOperation.getExpensiveString()); // ExpensiveOperation only executed if Optional is empty</code>

Test Case

To illustrate the difference, consider a function that returns an Optional string:

<code class="java">public Optional<String> findMyPhone(int phoneId) { ... }</code>

Scenario 1: orElse()

Optional.isPresent()	Used phone
True (redundant call)	NewExpensivePhone
False	NewExpensivePhone

Scenario 2: orElseGet()

Optional.isPresent()	Used phone
True	MyCheapPhone
False	NewExpensivePhone

As seen in the test case, orElse() always executes the provided function, while orElseGet() only executes it when needed.

Conclusion

Understanding the difference between orElse() and orElseGet() is crucial when working with Optionals. orElseGet() provides an efficient way to handle Optional values by avoiding unnecessary operations when the Optional is present.

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