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In object-oriented computer programming, a null object is an object with no referenced value or with defined neutral (null) behavior.The null object design pattern, which describes the uses of such objects and their behavior (or lack thereof), was first published as "Void Value" [1] and later in the Pattern Languages of Program Design book series as "Null Object".
In computing, a null pointer or null reference is a value saved for indicating that the pointer or reference does not refer to a valid object. Programs routinely use null pointers to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types ...
In object-oriented languages, access to objects is achieved through references (or, equivalently, pointers). A typical call is of the form: x.f(a, ...) where f denotes an operation and x denotes a reference to some object. At execution time, however, a reference can be void (or null).
The language does not provide any explicit pointer manipulation operators. It is still possible for code to attempt to dereference a null reference (null pointer), however, which results in a run-time exception being thrown. The space occupied by unreferenced memory objects is recovered automatically by garbage collection at run-time. [20]
In JavaScript, there are 7 primitive data types: string, number, bigint, boolean, symbol, undefined, and null. [19] Their values are considered immutable. These are not objects and have no methods or properties; however, all primitives except undefined and null have object wrappers. [20]
[1] The observer pattern addresses the following problems: [2] A one-to-many dependency between objects should be defined without making the objects tightly coupled. When one object changes state, an open-ended number of dependent objects should be updated automatically. An object can notify multiple other objects.
load onto the stack a reference from an array aastore 53 0101 0011 arrayref, index, value → store a reference in an array aconst_null 01 0000 0001 → null push a null reference onto the stack aload 19 0001 1001 1: index → objectref load a reference onto the stack from a local variable #index: aload_0 2a 0010 1010 → objectref
Finally, it increases type safety and can prevent problems due to null pointers [how?], labeled by C.A.R. Hoare—the null reference inventor—as "the billion dollar mistake" [2] From a Programming Languages perspective, it's reasonable to say that flow-sensitive typing is the feature that finally made it possible to build usable type-safe ...