How to Exit a Sub-Window When Displaying Multiple Windows in Processing 3

I also look at the site and actually use the improved class.
Add the following three methods to the SecondApplet class and it will work.

void exit(){
  dispos();
}

void close() {
  surface.setVisible(false);// Required to clear window
  dispos(); // Required to exit thread
}

void all_close(){
  System.exit(0);
}

When the ✖ button is pressed, exit() defined in the PApplet class is called, and perhaps something close to System.exit(0).Therefore, if exit() is overridden, everything will not disappear even if you close the window with ✖.However, to stop the thread, you need to call dispos().

Also implement the method of closing only the sub-window from the program (if necessary).I said close().By calling it an instance method, you can terminate only the subwindow from the outside.

Originally, I was able to terminate the program by calling exit(), but because of the override, I cannot terminate the program from the sub-window.You can exit the program by retrieving the PApplet of the main window (as parent), calling parent.exit(), or calling System.exit(0), just like that site.

The only answer to this question was the explanation of exit(), but I also introduced a method that might be relevant.
If you apply this, you can also delete the main window and leave only the sub-window.