When should I use Optional.orElseGet() instead of Optional.orElse() in Java?

Determining the Difference Between Optional.orElse() and Optional.orElseGet()

In Java, the Optional class provides methods like orElse() and orElseGet() for dealing with potentially missing or null values. Understanding their nuances is crucial for effective usage.

orElse() vs. orElseGet()

• orElse(): Returns the value if present, or the provided default if absent.
• orElseGet(): Returns the value if present, or the result of invoking the supplied supplier if absent. The supplier is not invoked if the value is present.

When to Use orElseGet()

• Performance Optimization: Consider using orElseGet() when the action to perform on a missing value is computationally expensive, as it avoids unnecessary execution in the isPresent() scenario.

Example with Real-World Function

To illustrate the difference, consider the following function:

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

Scenario 1: orElse()

When optional.isPresent() == true:

• orElse() will call the subsequent function redundantly, even if the value is already present.

When optional.isPresent() == false:

• orElse() will call the subsequent function regardless of its necessity.

Scenario 2: orElseGet()

When optional.isPresent() == true:

• orElseGet() will not invoke the supplier since the value is present.

When optional.isPresent() == false:

• orElseGet() will invoke the supplier to generate the default value.

Code Example

<code class="java">public class TestOptional {
    public Optional<String> findMyPhone(int phoneId) {
        return phoneId == 10
                ? Optional.of("MyCheapPhone")
                : Optional.empty();
    }

    public String buyNewExpensivePhone() {
        System.out.println("Going to a very far store to buy a new expensive phone");
        return "NewExpensivePhone";
    }

    public static void main(String[] args) {
        // Scenario 1: orElse()
        Optional<String> phone = findMyPhone(10).orElse(buyNewExpensivePhone());
        // Scenario 2: orElseGet()
        phone = findMyPhone(-1).orElseGet(() -> buyNewExpensivePhone());
    }
}</code>

The code demonstrates the different behaviors of orElse() and orElseGet() based on the presence or absence of the optional value.

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