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In computer programming, lazy initialization is the tactic of delaying the creation of an object, the calculation of a value, or some other expensive process until the first time it is needed.
Lazy loading (also known as asynchronous loading) is a technique used in computer programming, especially web design and web development, to defer initialization of an object until it is needed. It can contribute to efficiency in the program's operation if properly and appropriately used.
For example, to undo a delete selection command, the object may contain a copy of the deleted text so that it can be re-inserted, if the delete selection command must be undone. Note that using a separate object for each invocation of a command is also an example of the chain of responsibility pattern. The term execute is also ambiguous.
Python's is operator may be used to compare object identities (comparison by reference), and comparisons may be chained—for example, a <= b <= c. Python uses and, or, and not as Boolean operators. Python has a type of expression named a list comprehension, and a more general expression named a generator expression. [78]
A singleton implementation may use lazy initialization in which the instance is created when the static method is first invoked. In multithreaded programs, this can cause race conditions that result in the creation of multiple instances. The following Java 5+ example [6] is a thread-safe implementation, using lazy initialization with double ...
Lazy evaluation can also lead to reduction in memory footprint, since values are created when needed. [19] In practice, lazy evaluation may cause significant performance issues compared to eager evaluation. For example, on modern computer architectures, delaying a computation and performing it later is slower than performing it immediately.
The observer design pattern is a behavioural pattern listed among the 23 well-known "Gang of Four" design patterns that address recurring design challenges in order to design flexible and reusable object-oriented software, yielding objects that are easier to implement, change, test and reuse.
The bridge pattern is a design pattern used in software engineering that is meant to "decouple an abstraction from its implementation so that the two can vary independently", introduced by the Gang of Four. [1]