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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 ...
Thus, one can use threads without paying the cost of creation and disposal of threads. The following shows the basic code of the object pool design pattern implemented using C#. For brevity the properties of the classes are declared using C# 3.0 automatically implemented property syntax.
In Ruby, all classes are open. In Python, classes can be created at runtime, and all can be modified afterward. [43] Objective-C categories permit the programmer to add methods to an existing class without the need to recompile that class or even have access to its source code.
According to Design Patterns: Elements of Reusable Object-Oriented Software: "Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory method lets a class defer instantiation to subclasses." [2] Creating an object often requires complex processes not appropriate to include within a composing object.
Since 7 October 2024, Python 3.13 is the latest stable release, and it and, for few more months, 3.12 are the only releases with active support including for bug fixes (as opposed to just for security) and Python 3.9, [55] is the oldest supported version of Python (albeit in the 'security support' phase), due to Python 3.8 reaching end-of-life.
Also, another common example is that a person object created from a child class cannot become an object of parent class because a child class and a parent class inherit a person class but class-based languages mostly do not allow to change the kind of class of the object at runtime. For class-based languages, this restriction is essential in ...
Inner classes became a feature of the Java programming language starting with version 1.1. Nested classes are also a feature of the D programming language, Visual Basic .NET, Ruby, C++ and C#. In Python, it is possible to nest a class within another class, method or function.
Object pool pattern: avoid expensive acquisition and release of resources by recycling objects that are no longer in use; Prototype pattern: used when the type of objects to create is determined by a prototypical instance, which is cloned to produce new objects; Singleton pattern: restrict instantiation of a class to one object