How do i check if an object has been created?

[George Papadopoulos]

Hallo!
In my application if a button is pressed a new object is created.
i want my button to stay enabled but if the user presses it again i want to display an error message.
what do i put into the if statement to check if the object has already been created?
Thanx a lot!

[Mike Southgate]

sounds to me like your looking for a variation of the singleton pattern. But the easiest way is to simply create a has-a relationship with the caller and then check it for == NULL
ms

[sever oon]

You can check the reference to the object for null:

Object o = null;
// when button gets pressed, o = new Object();
// sometime later...
if( o == null ) {
  // button hasn't been pressed yet
}
else {
  // button was pressed
}

It's bizarre to me that you specifically said you want to leave the button enabled even though it will definitely result in an error if the user presses it. This sounds like a pretty hostile UI. Disable it, and enable it only when pressing it won't result in an error.
sev