Consider the following implementation of Singleton
Pattern.
class SingletonException extends RuntimeException
{
//new exception type for singleton classes
public SingletonException()
{
super();
}
//-----------------------------------------------
public SingletonException(
String s)
{
super(s);
}
}
class PrintSpooler
{
//this is a prototype for a printer-spooler class
//such that only one instance can ever exist
static boolean
instance_flag=false; //true if 1 instance
public PrintSpooler() throws SingletonException
{
if (instance_flag)
throw new SingletonException("Only one spooler allowed");
else
instance_flag = true; //set flag for 1 instance
System.out.println("spooler opened");
}
//-------------------------------------------
public void finalize()
{
instance_flag = false; //clear if destroyed
}
}
//-----------------------------------------------------------------------
Here we are using finalize method to reset the instance_flag variable so that we are able to create a instance if no instance is in Existance.
My question is
Since we cannot rely on finally method to be executed everytime
how do we make sure that the instance_flag is reset ?
is it possible to implement Singleton pattern without any ambiquity?
Thanks,
Pramod.
