Calling commands from a button

You can call a command, e.g. in this example "add.command" from a button via the following coding.

   
button.addSelectionListener(new SelectionAdapter() {

   @Override
   public void widgetSelected(SelectionEvent e) {
    IHandlerService handlerService = (IHandlerService) getSite()
      .getService(IHandlerService.class);
    try {
     handlerService.executeCommand("add.command", null);
    } catch (Exception ex) {
     throw new RuntimeException("add.command not found");
    }

   }
  });