What is singleton design pattern ?

Singleton design pattern is type of Creational Design pattern . It creates a single instance object which caters to all the clients.

Singleton Design pattern has :

1. It has private constructor so that instance of class cannot be created anywhere but inside its own methods.
2. It has static read only member so that instance is created only once .
3. It has an instance property to return singleton object instance

 Code snippet for simple singleton :
public sealed class Singleton
{
// private constructor
private Singleton()
{
}
// static readonly member
static readonly Singleton instance = new Sinleton();
// static instance property
public static Singleton Instance
{
get { return instance ; }
}

}