ui/src/main/java/ucar/util/prefs/ui/PrefPanel.java
static public Frame findActiveFrame() {
    Frame[] frames = JFrame.getFrames();
    for (Frame frame : frames) {
      if (frame.isVisible())
        return frame;
    }
    return null;
  }
static public Frame findActiveFrame() {
    Frame[] frames = JFrame.getFrames();
    for (Frame frame : frames) {
      if (frame.isVisible())
        return frame;
    }
    return null;
  }
static public Frame findActiveFrame ( ) { Frame [ ] frames = JFrame . getFrames ( ) ; for ( Frame frame : frames ) { if ( frame . isVisible ( ) ) return frame ; } return null ; }
thanks to Heinz M. Kabutz
thanks to Heinz M . Kabutz