4 of 23 Design Patterns in Java-singleton mode (singleton pattern)

As an object's creation mode, Singleton mode ensures that a class has only one instance, and instantiates itself and provides this instance to the system as a whole.

A singleton class can have only one instance.

The Singleton class must create its own unique instance.

The Singleton class must provide this instance to all other objects.

Typically, the constructor is described by private, prohibiting the external construction of the object and obtaining a unique instance through getinstance.

Class Singleton
{
private static Singleton Asingleton=null;
private static int indexsingleton=0;
Private Singleton ()
{
indexsingleton++;
}
public static Singleton getinstance ()
{
if (asingleton==null)
Asingleton=new Singleton ();
return Asingleton;
}
public void Printinfo ()
{
SYSTEM.OUT.PRINTLN ("Singleton index:" +indexsingleton);
}
}

public class Singletonpatterntest
{
public static void Main (string[] args)
{
Singleton asingleton=singleton.getinstance ();
Asingleton.printinfo ();
Singleton bsingleton=singleton.getinstance ();
Bsingleton.printinfo ();
}
}

//////////////////////////////////

Output Result:

Singleton index:1
Singleton index:1

4 of 23 Design Patterns in Java-singleton mode (singleton pattern)