Noninstantiability

Noninstantiability is a design property of a class or module that forbids creating instances of it, so its behavior is accessed only through its static members or as a namespace.

In object-oriented programming, noninstantiable classes are typically used to group related utility functions or constants without maintaining per-object state. A common implementation in languages like Java is to declare the class as final and provide a private constructor, sometimes with a deliberate exception to deter reflection: private ClassName() { throw new AssertionError("No instances"); }. This approach prevents both instantiation and subclassing.

Other languages offer similar patterns. In C++, a class can hide its constructors or explicitly delete them to prevent instantiation. In Python, a module can serve as a noninstantiable namespace, or a class can raise an exception in __new__ to block creation.

Noninstantiability communicates intent and can prevent accidental misuse, but it does not imply the absence of state or side effects in the surrounding system; it also does not guarantee security against reflection or metaprogramming. Design decisions surrounding noninstantiability often hinge on whether a class should be purely a collection of static utilities, act as a namespace, or participate in inheritance hierarchies. In some cases, equivalent semantics are achieved instead by using modules or namespaces that provide the same functional grouping without relying on instance creation.

See also: Utility class, static class.