isEmpty

IsEmpty is a common predicate in programming used to determine whether a container-like object has no elements. It is implemented as a method or function on many data types, including strings, arrays, lists, maps, and sets. When isEmpty returns true, the object contains zero elements; when false, it contains at least one element. For strings, emptiness typically means the string has zero characters; for collections, it means the number of elements is zero.

Language-specific notes:

In Java, String has isEmpty(), which returns true if length() is 0. Subtypes of Collection also provide isEmpty(); for arrays, there is no isEmpty method and you usually check array.length == 0. In Python, there is no isEmpty method; emptiness is tested with len(x) == 0 for sequences and mappings. In JavaScript, emptiness is checked by inspecting length for strings and arrays; for plain objects you commonly use Object.keys(obj).length === 0; Map and Set expose a size property, so map.size === 0 or set.size === 0 checks emptiness. In Ruby, empty? is a common method on Strings, Arrays, and Hashes, returning true when there are no characters or elements. In C++, containers provide empty() as a member function, typically mirroring size() == 0; arrays do not have an empty() member, so size checks are used instead.

Edge cases and performance:

Nullability matters: calling isEmpty on a null reference usually results in an error; frameworks sometimes offer safe checks or optional types to handle nulls gracefully. In well-designed containers, isEmpty is typically an O(1) operation, since it usually consults a stored size or length rather than counting elements.

See also: isNotEmpty, isBlank, and size or length checks.