When to Use `Optional.orElseGet()` Over `Optional.orElse()`?

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

The Optional class in Java provides convenient methods for handling and returning values that may or may not be present. Two important methods in this class are orElse() and orElseGet(). The primary difference between these methods lies in the timing of when the fallback value or computation is invoked.

orElse()

The orElse() method takes a default value as an argument and returns that value if the Optional instance is empty. It does not wait for isPresent() to be evaluated, but immediately evaluates and returns the provided fallback value, even if the Optional instance is not empty.

orElseGet()

In contrast, the orElseGet() method takes a Supplier interface as an argument, allowing you to define a computation that only runs when the Optional instance is empty. This approach is more efficient when the fallback value is expensive to compute and should only be performed when necessary.

When to Use orElseGet() Over orElse()

Consider using orElseGet() instead of orElse() in the following scenarios:

• Performance Optimization: orElseGet() ensures that the fallback computation is only performed when needed, improving performance if the fallback computation is resource-intensive.
• Exception Handling: If the fallback computation can throw an exception, orElseGet() allows you to wrap it in a more controlled manner, avoiding any unexpected exceptions from being thrown.
• Code Readability: Using orElseGet() with a descriptive Supplier can improve code readability by indicating when the fallback computation is being executed.

Example Usage

Consider the following example:

<code class="java">Optional<String> optional = Optional.ofNullable("Hello");

// Always computes the fallback value.
String result1 = optional.orElse("World");

// Computes the fallback value only if the optional is empty.
String result2 = optional.orElseGet(() -> {
   // Expensive computation here
   return "World";
});</code>

In this example, result1 will always contain "World" because the fallback value is evaluated regardless of the option being present. On the other hand, result2 will only be assigned "World" if the optional is empty, allowing for better performance when the computation is expensive.

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