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Complete article "Java Singleton Pattern Explained" Four different ways to implement singleton in Java "Ways to implement singleton in Java" Book extract: Implementing the Singleton Pattern in C# by Jon Skeet; Singleton at Microsoft patterns & practices Developer Center; IBM article "Double-checked locking and the Singleton pattern" by Peter Haggar
This pattern can be implemented in several ways depending on the host programming language, such as the singleton design pattern, object-oriented static members in a class and procedural global functions. In Python, the pattern is built into the language, and each .py file is automatically a module.
The single-serving visitor pattern should be used when visitors do not need to remain in memory. This is often the case when visiting a hierarchy of objects (such as when the visitor pattern is used together with the composite pattern) to perform a single task on it, for example counting the number of cameras in a 3D scene.
Design Patterns: Elements of Reusable Object-Oriented Software (1994) is a software engineering book describing software design patterns. The book was written by Erich Gamma , Richard Helm , Ralph Johnson , and John Vlissides , with a foreword by Grady Booch .
In software engineering, the multiton pattern is a design pattern which generalizes the singleton pattern. Whereas the singleton allows only one instance of a class to be created, the multiton pattern allows for the controlled creation of multiple instances, which it manages through the use of a map .
In a software design pattern view, lazy initialization is often used together with a factory method pattern. This combines three ideas: Using a factory method to create instances of a class (factory method pattern) Storing the instances in a map, and returning the same instance to each request for an instance with same parameters (multiton pattern)
In PHP, the unit type is called null, which only value is NULL itself. In JavaScript, both Null (its only value is null) and Undefined (its only value is undefined) are built-in unit types. in Kotlin, Unit is a singleton with only one value: the Unit object. In Ruby, nil is the only instance of the NilClass class.
The observer pattern, as described in the Design Patterns book, is a very basic concept and does not address removing interest in changes to the observed subject or special logic to be performed by the observed subject before or after notifying the observers. The pattern also does not deal with recording change notifications or guaranteeing ...