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Check that the variable is initialized (without obtaining the lock). If it is initialized, return it immediately. Obtain the lock. Double-check whether the variable has already been initialized: if another thread acquired the lock first, it may have already done the initialization. If so, return the initialized variable.
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 object-oriented programming, the safe navigation operator (also known as optional chaining operator, safe call operator, null-conditional operator, null-propagation operator) is a binary operator that returns null if its first argument is null; otherwise it performs a dereferencing operation as specified by the second argument (typically an ...
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 ...
It is often abbreviated as NUL (or NULL, though in some contexts that term is used for the null pointer). In 8-bit codes, it is known as a null byte . The original meaning of this character was like NOP —when sent to a printer or a terminal , it has no effect (some terminals, however, incorrectly display it as space ).
In computer programming, specifically when using the imperative programming paradigm, an assertion is a predicate (a Boolean-valued function over the state space, usually expressed as a logical proposition using the variables of a program) connected to a point in the program, that always should evaluate to true at that point in code execution.
Valhalla is incubating Java language features and enhancements in these areas: [2] [3] Value Classes and Objects: highly-efficient objects without their own identity (reference value). Null-restricted and Nullable types, and Null-restricted Objects: for example, using ? or ! after type declaration to say if null is allowed or not.
Short-circuit evaluation, minimal evaluation, or McCarthy evaluation (after John McCarthy) is the semantics of some Boolean operators in some programming languages in which the second argument is executed or evaluated only if the first argument does not suffice to determine the value of the expression: when the first argument of the AND function evaluates to false, the overall value must be ...