protected Command getCommand() {
		Command command = null;
		
		IWorkbench workbench = PlatformUI.getWorkbench();
		if(workbench != null) {
			IWorkbenchWindow activeWorkbenchWindow = workbench.getActiveWorkbenchWindow();
			if(activeWorkbenchWindow != null) {
				Object service = activeWorkbenchWindow.getService(ICommandService.class);
				if(service != null && service instanceof ICommandService) {
					ICommandService commandService = (ICommandService)service;
					
					//COMMAND_ID is defined in plugin.xml with defaultHandler class
					command = commandService.getCommand(COMMAND_ID);
				}
			}
		}
		
		return command;		
	}	

The data object to pass to the command (and its handler) as it executes.

	/**
	 * Executes with the map of parameter values by name.
	 * 
	 * @param event
	 *            An event containing all the information about the current
	 *            state of the application; must not be <code>null</code>.
	 * @return the result of the execution. Reserved for future use, must be
	 *         <code>null</code>.
	 * @throws ExecutionException
	 *             if an exception occurred during execution.
	 */
	Object execute(ExecutionEvent event) throws ExecutionException;

public interface IHandler {
	void addHandlerListener(IHandlerListener handlerListener);

	public void dispose();

	Object execute(ExecutionEvent event) throws ExecutionException;

	public boolean isEnabled();

	public boolean isHandled();

	void removeHandlerListener(IHandlerListener handlerListener);
}

public void selectionChanged(SelectionChangedEvent event);

public interface IHandler {
	void addHandlerListener(IHandlerListener handlerListener);

	public void dispose();

	Object execute(ExecutionEvent event) throws ExecutionException;

	public boolean isEnabled();

	public boolean isHandled();

	void removeHandlerListener(IHandlerListener handlerListener);

	public void selectionChanged(SelectionChangedEvent event);
}