Finalizer

In computer science, a finalizer or finalize method is a special method that performs finalization, generally some form of cleanup. A finalizer is executed during object destruction, prior to the object being deallocated, and is complementary to an initializer, which is executed during object creation, following allocation. Finalizers are strongly discouraged by some, due to difficulty in proper use and the complexity they add, and alternatives are suggested instead, mainly the dispose pattern (see problems with finalizers). The term finalizer is mostly used in object-oriented and functional programming languages that use garbage collection, of which the archetype is Smalltalk. This is contrasted with a destructor, which is a method called for finalization in languages with deterministic object lifetimes, archetypically C++. These are generally exclusive: a language will have either finalizers (if automatically garbage collected) or destructors (if manually memory managed), but in rare cases a language may have both, as in C++/CLI and D, and in case of reference counting (instead of tracing garbage collection), terminology varies. In technical use, finalizer may also be used to refer to destructors, as these also perform finalization, and some subtler distinctions are drawn – see terminology. The term final is also used to indicate a class that cannot be inherited; this is unrelated. The terminology of finalizer and finalization versus destructor and destruction varies between authors and is sometimes unclear. In common use, a destructor is a method called deterministically on object destruction, and the archetype is C++ destructors; while a finalizer is called non-deterministically by the garbage collector, and the archetype is Java finalize methods. For languages that implement garbage collection via reference counting, terminology varies, with some languages such as Objective-C and Perl using destructor, and other languages such as Python using finalizer (per spec, Python is garbage collected, but the reference CPython implementation since its version 2.