OrElseGet

OrElseGet is a method of the Java Optional class that provides a way to obtain the contained value or generate an alternative lazily. It was introduced in Java 8 as part of the java.util.Optional API, which supports the handling of optional values without resorting to null checks.

The primary behavior of orElseGet is straightforward: if the Optional contains a value, that value is returned unchanged. If the Optional is empty, the method calls a supplied Supplier to produce a replacement value, which is then returned. The key distinction from orElse is that orElseGet defers the computation of the alternative until it is actually needed, avoiding potentially expensive operations when a value is present.

The method signature is public T orElseGet(Supplier<? extends T> other), where T is the type contained in the Optional. The supplier is an implementation of java.util.function.Supplier with a single method get() that returns a value of type T. Because the supplier is invoked only when the Optional is empty, orElseGet is useful for lazy evaluation and performance optimization.

Example usage can be concise: Optional<String> opt = Optional.ofNullable(name); String display = opt.orElseGet(() -> fetchFromDatabaseOrDefault(name)); If name is present, display holds that value; otherwise, the supplier computes a fallback.

Notes: orElseGet may throw unchecked exceptions if the supplier does; checked exceptions are not part of the Supplier contract and must be handled within the supplier. The method provides a lazy alternative to orElse and is commonly contrasted with orElseThrow for cases where an exception should be produced when no value is present.