Difference between revisions of "Singleton Design Pattern"
From JholJhapata
(Created page with "The singleton pattern is a software design pattern that restricts the instantiation of a class to one single instance. This is useful when exactly one object is needed to coor...") |
|||
| Line 1: | Line 1: | ||
The singleton pattern is a software design pattern that restricts the instantiation of a class to one single instance. This is useful when exactly one object is needed to coordinate actions across the system. | The singleton pattern is a software design pattern that restricts the instantiation of a class to one single instance. This is useful when exactly one object is needed to coordinate actions across the system. | ||
| + | [[File:Singleton.png|thumb|Singleton]] | ||
| + | == Problem == | ||
| + | Application needs one, and only one, instance of an object. | ||
| + | ==== Example ==== | ||
| + | Let’s take a look at an example, which is creating multiple objects. | ||
| + | |||
| + | class Program | ||
| + | { | ||
| + | static void Main(string[] args) | ||
| + | { | ||
| + | SingleTon obj1 = new SingleTon(); | ||
| + | SingleTon obj2 = new SingleTon(); | ||
| + | Console.WriteLine("Main End"); | ||
| + | Console.ReadLine(); | ||
| + | } | ||
| + | } | ||
| + | class SingleTon | ||
| + | { | ||
| + | private static int objectCounter = 0; | ||
| + | public SingleTon() | ||
| + | { | ||
| + | objectCounter++; | ||
| + | Console.WriteLine("objectCounter : " + objectCounter.ToString()); | ||
| + | } | ||
| + | public void printText(string strData) | ||
| + | { | ||
| + | Console.WriteLine(strData); | ||
| + | } | ||
| + | } | ||
| + | ==== Output ==== | ||
| + | objectCounter : 1 | ||
| + | objectCounter : 2 | ||
| + | Main End | ||
| + | == Solution == | ||
| + | The common characteristics of a Singleton Pattern: | ||
| + | * A single constructor, that is private and parameter-less. | ||
| + | * The class is sealed. | ||
| + | * A static variable that holds a reference to the single created instance, if any. | ||
| + | * A public static means of getting the reference to the single created instance, creating one if necessary. | ||
| + | === First version - not thread-safe === | ||
| + | ==== Output ==== | ||
| + | === Second version - simple thread-safety === | ||
| + | ==== Output ==== | ||
| + | === Third version - attempted thread-safety using double-check locking === | ||
| + | ==== Output ==== | ||
| + | == Singleton class vs. Static class == | ||
Revision as of 17:49, 9 December 2019
The singleton pattern is a software design pattern that restricts the instantiation of a class to one single instance. This is useful when exactly one object is needed to coordinate actions across the system.
Contents
Problem
Application needs one, and only one, instance of an object.
Example
Let’s take a look at an example, which is creating multiple objects.
class Program
{
static void Main(string[] args)
{
SingleTon obj1 = new SingleTon();
SingleTon obj2 = new SingleTon();
Console.WriteLine("Main End");
Console.ReadLine();
}
}
class SingleTon
{
private static int objectCounter = 0;
public SingleTon()
{
objectCounter++;
Console.WriteLine("objectCounter : " + objectCounter.ToString());
}
public void printText(string strData)
{
Console.WriteLine(strData);
}
}
Output
objectCounter : 1 objectCounter : 2 Main End
Solution
The common characteristics of a Singleton Pattern:
- A single constructor, that is private and parameter-less.
- The class is sealed.
- A static variable that holds a reference to the single created instance, if any.
- A public static means of getting the reference to the single created instance, creating one if necessary.
