SWT Java Tutorial

The primary functions of Display instances are as follows:
The Display object is the connection between the SWT and the underlying windowing system.
Implementing the SWT event loop in terms of a platform event model
Providing methods for accessing information about the operating system
Managing operating system resources used by SWT
Only a single Display instance is required in most SWT-based applications.
The thread that creates the Display object is the event-loop thread (user-interface thread).