I want to run single instance of my class ?

Question

i have a class with name Abc, i want when my Abc class is
in running mode then i cant run my Abc class again untill my
Abc class not exit.
i want to do that in pure java, i have one logic but it is not
proper salution.
my logic is that when my programe is start first check a temprery file
which is created by my programe and when i want to exit then i delete
that temprery file.
but if computer is shutdown unproperly and my programe is in running mode then my file is not delete.
please any body give me help.
i m thanksfull.
Arif.

Answer 1

Hi,
let's make it more precise as so "if my class is in running mode" is not very precise - I guess, you are not talking of a class which has implemented the Runnable interface and is executed via "new Thread(Abc).start()". I think, you want a class, which can only have one instance of it at a time, right?
It is no problem, to make a class, which has only one instance - it is called a Singleton class - it consists of the following:
public class MySingleton extends Object // or any other class
public static final instance = new MySingleton();
//the trick here is to declare its constructor private
private MySingleton() { super(); }
// some other methods here
}There is only one instance of this class accessible via MySingleton.instance. The problem with it is, that it doesn't match your requirements, as so you are not able to instantiate this class ever again, even so you would declare the "instance" field not final and set it to null.
What you can do now is dealing with security managers - check the documentation of the newInstance() method of the Class class and the SecurityManager class, there you will find several links to documentation related with the use of an security manager.
greetings Marsian
P.S.: all these *** in the text are the letters a s s :(