How to Use the orElse Method with Java 8 Stream API

What is the purpose of the orElse method in Java 8 Stream API?

Optional<String> optionalValue = Optional.ofNullable(value);
String result = optionalValue.orElse("default value");

In Java 8, the Stream API provides powerful tools for processing sequences of elements. One of these tools is the Optional class, which can represent a value that may or may not be present. The orElse method is used to provide a default value when an optional does not contain a value.

// Example of using orElse with a Stream
List<String> list = Arrays.asList("a", "b", null);
String value = list.stream()
                  .filter(Objects::nonNull)
                  .findFirst()
                  .map(String::toUpperCase)
                  .orElse("DEFAULT");
System.out.println(value); // Output: DEFAULT

Causes

• The value might not exist, leading to the need for a fallback.
• Commonly used in situations where you want to avoid NullPointerExceptions by explicitly handling null values.

Solutions

• Use the orElse method to specify a default value when an optional is empty.
• Chain orElse with Filter and Map operations in Streams to enhance computations.

Mistake: Using orElse with an Optional that always has a value, resulting in unnecessary code for the default value.

Solution: Evaluate if you actually need to use orElse; use ifPresent or isPresent for conditional handling instead.

Mistake: Assuming orElse will throw an exception if the value is absent. It simply returns the provided default value.

Solution: Understand that orElse is designed to handle absence of value gracefully without exceptions.