orElseThrowSupplier

orElseThrowSupplier is a term used to describe the practice of providing an exception to be thrown when an Optional is empty. It is not a separate API but relies on the exception-supplier argument of the Optional.orElseThrow method available in Java 8 and later. The orElseThrow method takes a Supplier<? extends Throwable> and, if the Optional has a value, returns that value; if empty, it invokes the supplier to obtain the exception to throw and propagates it.

Typical usage involves passing a lambda or method reference that constructs the desired exception. For example, optional.orElseThrow(() -> new NoSuchElementException("Value not present")). This pattern is often referred to as orElseThrowSupplier because the lambda acts as a supplier of the exception to throw.

A common extension is to factor out exception construction into reusable suppliers to avoid duplicating messages. For instance, static Supplier<IllegalArgumentException> missingValue(String field) { return () -> new IllegalArgumentException(field + " is missing"); } then optional.orElseThrow(missingValue("name")). When using a checked exception, the type parameter of orElseThrow must be coordinated with the throwing method’s signature, since orElseThrow declares it can throw a checked Throwable.

Advantages of this approach include lazy construction of exceptions (the exception object is created only if needed) and clear separation between presence checks and error handling. Limitations include the need to manage exception types and the potential confusion of readers unfamiliar with the supplier pattern.

See also Optional.orElseThrow, Supplier, Java Optional.

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