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The singleton pattern is a programming concept that allows programs to access a specific set of information only once and always contain the same set of instructions or information. It is used to define a global variable, which stays the same and only needs to be defined once. This saves space in computer memory and increases speed.
The mathematical concept of a singleton is a set of numbers that contains only one number. Software engineers and programmers have translated this concept into something called a singleton pattern, in which various programs access a specific set of information only once and always contain the same set of instructions or information. The singleton pattern is used in programming languages such as Java to define a global variable, a piece of information used throughout an entire system that stays the same and only needs to be defined once rather than many times.
In most programming languages, before a program can run, it requires more information about its environment. Most of the program-specific information is contained within its own program code; however, a program also often requires variable information about things like the version of the operating system it’s running on, the hardware it’s running on, and other specific information that isn’t unique to the program itself. Usually this information is contained in something called a class or object, which is an independent piece of programming code often contained in a separate file from the program so that it can be available to many different programs at once.
If a programming language doesn’t use the singleton pattern, any program that requests information contained in an object accesses it by opening the object with a set of parameters that specify what information in the object the program needs. Therefore, each time a different program opens the object, a different instance of the object is created in computer memory. Each instance of the object can contain different information, depending on the specific needs of each program that opens it.
When a programming language that uses the singleton pattern, such as Java, starts executing a program, the program first looks for the objects it needs information from. If an object is not already open, opens the object without specific parameters, making all the information contained in the object available to all programs. If the object is already open, it simply reads the information in the object and continues. This way, the information contained in an object using a singleton pattern is always the same, so you don’t have to open many different versions of the object at the same time. This saves space in your computer’s memory and can also increase speed because other programs can access the information without having to spend time creating a new version of the object.
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