Need help.....

[Elahe Shafie]

Ho dear Friends,
I don't understand what is the second line for?could you please help me to describe second line?
Many thanks,
Elahe
---------------------------
public class DbManager {
private static DbManager oSingle = null;

[Mike Curwen]

that's the start of a Singleton pattern.

public class Singleton {
 
   private static Singleton instance = null;
 
   protected Singleton() {
     // whatever...
   }
 
   public static Singleton instance() {
      if(instance==null) {
         instance = new Singleton();
      }
      return instance;
   }
 
}

This ensures that only a single instance of this class is possible.

Because the constructor is protected (or private), code using this class cannot do this:

Singleton one = Singleton();
Singleton two = Singleton();

The user of this class is forced to use the static method that gets the internal instance. The internal instance is also declared static, because the static method needs access to it.

Singleton one = Singleton.instance();
Singleton two = Singleton.instance();  

In this case, both one and two refer to the same instance, and not two different ones.
[ March 01, 2002: Message edited by: Mike Curwen ]

[Mike Curwen]

Moving this from Servlets -> Java in General (Beginners)