How to check if an object exists and how to discard it?

Question

Greetings,
I have a main GUI panel in a JFrame that creates a smaller JFrame with a progress bar and text area whenever a process is initiated. I've set the default close operation to DISPOSE_ON_CLOSE as when I set it to EXIT_ON_CLOSE the main GUI panel closes as well (!). But whenever I'm closing the smaller JFrame and initiate a new thread, then the same operation is perform in parallel 2, 3 ,4 times, etc. It seems that the object of the class ProgressGUI which carries all the components of the small panel is not disposed properly. So my question is how can I check if an object exists and if yes how can I discard it? Or in other words how can I discard the JFrame of the small panel without closing the main GUI panel as well?
thanks,
Thomas

Answer 1

I've set the default close operation to DISPOSE_ON_CLOSE thats right.
So my question is how can I check if an object exists Whenever you create an object, save its refrence somewhere, then just check
if(reference==null){
         //object does not exist
}else {
        //object exists
and if yes how can I discard it? Ensure that no references of the object to be discarded are remaining with any of the objects and then believe in 'Garbage Collector' to do the job! e.g. if there is only one reference to the frame (in your case) somewhere, you can just make an assignment like:
reference=null;by doing this, you have made the object a candidate for garbage collection. Rest is done by 'Garbage Collector', not you.
For cases like yours, it is better to make the small frame just once and whenever required just make the frame visible.
e.g.
JFrame smallFrame;
void showSmallFrame(){
    if(smallFrame==null)smallFrame=new SmallFrame(); //or something like that
    smallFrame.setVisible(true);
}Thanks!