Singleton pattern ensures a class can have only single
instance during the lifetime of an application.
When to use Singleton Pattern?
When you want to create single object only once during application life you can go with Singleton Pattern. The implementation and use of singleton pattern is very easy. See below example.
Code –
public class Singleton
{
//private static
member.
private static Singleton
instance;
//Private
constructor prevents instance creation of class from outside.
private
Singleton() { }
//This static
method responsible for creation of instance of this class.
public static Singleton
GetInstance()
{
//create new
instance only in first call, rest of the time it will return existing object
if
(instance == null)
instance = new
Singleton();
return
instance;
}
public void Display()
{
Console.WriteLine("Display Method called from Singleton Class...");
}
}
class Program
{
static void Main(string[]
args)
{
Singleton
singleObject = Singleton.GetInstance();
singleObject.Display();
Console.Read();
}
}
Output –
Another way (via Property) to implement singleton pattern.
public class Singleton
{
//private static member.
private static Singleton
instance;
//Private
constructor prevents instance creation of class from outside.
private
Singleton() { }
//This static
method responsible for creation of instance of this class.
public static Singleton
Instance
{
get
{
//create
new instance only in first call, rest of the time it will return existing
object
if
(instance == null)
instance = new Singleton();
return
instance;
}
}
public void Display()
{
Console.WriteLine("Display Method called from Singleton Class...");
}
}
class Program
{
static void Main(string[]
args)
{
Singleton
singleObject = Singleton.Instance;
singleObject.Display();
Console.Read();
}
}
Output –
Same as above example.
Advantages -
- Class can perform additional functionalities other than creation of an object.
- This is referred as Lazy Initialization approach since instance of an object is not created until user call instance property or method. This approach avoids instantiating singletons class when application starts.
Disadvantage -
- Singleton pattern is not thread safe by default. You need to write additional code to make it thread safe. I'll post article for Thread safe singleton pattern in few days.
Hope you liked this article. Please leave your feedback.
References –
See Also –
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Creational Patterns
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Structural Patterns
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Behavioral Patterns
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