How can I determine what process a window belongs to?

Use Process Explorer, it allows you to identify the window and then you can check the properties of the process to figure out the command line used. This command line will help you determine what exactly has been launched, this helps to figure out where Java applications and scripts are located...

Just drag the icon over the window.

For a complete list of start-up applications, services and drivers; check Autoruns.

Swing seems it belongs to JAVA. Look for a java(w).exe. You can also see what process it belongs to by using the task manager. Go to "tasks", right click the window and choose "switch to process", it'll show you what process it is.

I'm not too sure if this works for Java applications, but you can call up Task Manager, under the Applications tab, right-click Go to process, which highlights the offending process in the Processes tab. You can then kill it.

For Windows 10

You can call up Task Manager, under the Users tab (or Processes tab, either is fine), right-click Go to details, which highlights the offending process in the Details tab. You can then kill it.