Optionals — cheat sheet

From: fundamentals/07-optionals.md.

• What it is: a container that either holds a value or is empty — a method returns Optional<T> instead of T when it might legitimately have nothing to give back. The method signature itself then tells callers "check before you use this," instead of relying on convention or documentation.
• Creating: Optional.of(value) when there's something to return, Optional.empty() when there isn't. No new + constructor — only these static factories.
• Using: isPresent() / isEmpty() to check, get() to unwrap once you know it's present, orElse(fallback) to unwrap with a default if empty.
• Where to use it: only as a return type, for methods that sometimes genuinely have nothing to return. Not for method parameters (except in test code) and not for fields on data classes.
• Why not just null?: before Java 8, null was the only way to represent "nothing," and it could appear almost anywhere with no signal in the method signature — leading to defensive null-checking everywhere ("null paranoia"), since you could never be sure from the signature alone whether a given call might return null. Optional makes the "might be empty" case explicit and type-checked instead of implicit and undocumented.