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In software engineering, the initialization-on-demand holder (design pattern) idiom is a lazy-loaded singleton. In all versions of Java, the idiom enables a safe, highly concurrent lazy initialization of static fields with good performance. [1] [2]
A class diagram exemplifying the singleton pattern. In object-oriented programming, the singleton pattern is a software design pattern that restricts the instantiation of a class to a singular instance. It is one of the well-known "Gang of Four" design patterns, which describe how to solve recurring problems in object-oriented software. [1]
Factories are used in various design patterns, specifically in creational patterns such as the Design pattern object library. Specific recipes have been developed to implement them in many languages. For example, several GoF patterns, like the Factory method pattern, the Builder or even the Singleton are implementations of this concept.
The original form of the pattern, appearing in Pattern Languages of Program Design 3, [2] has data races, depending on the memory model in use, and it is hard to get right. Some consider it to be an anti-pattern. [3] There are valid forms of the pattern, including the use of the volatile keyword in Java and explicit memory barriers in C++. [4]
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)
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. Rather than having a single instance per application (e.g. the java.lang.Runtime object in the Java programming language) the multiton pattern instead ...
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, a software design pattern or design pattern is a general, reusable solution to a commonly occurring problem in many contexts in software design. [1] A design pattern is not a rigid structure that can be transplanted directly into source code. Rather, it is a description or a template for solving a particular type of ...