Optional<T>: a container for absent values

Optional is a single-element box that might be empty

Optional<T> wraps a value that might not exist, making the possibility of absence explicit in the type rather than hidden in a null convention.

Creating Optionals:

Optional<String> present  = Optional.of("Ada");      // value must be non-null
Optional<String> maybe    = Optional.ofNullable(name); // null → empty
Optional<String> empty    = Optional.empty();

Querying:

if (opt.isPresent()) { String s = opt.get(); }  // classic — but verbose
opt.ifPresent(System.out::println);              // cleaner: callback if present

Extracting with a fallback:

String val1 = opt.orElse("default");              // always evaluates the arg
String val2 = opt.orElseGet(() -> compute());     // lazy: only calls if empty
String val3 = opt.orElseThrow();                  // throws if empty

Transforming:

Optional<Integer> length = opt.map(String::length);  // still Optional
Optional<String>  upper  = opt.filter(s -> s.length() > 3)
                              .map(String::toUpperCase);

map on an empty Optional returns empty — the chain short-circuits safely. flatMap is for when the mapping function itself returns an Optional (avoids Optional<Optional<T>>).