generateButton = new Button(top, SWT.PUSH);
		generateButton.setText("Generate Ecore");
		generateButton.setLayoutData(gridData);

		Listener listener = new Listener() {
			public void handleEvent(Event event) {
				if (event.widget == generateButton) {
					// here u must reach Part2's Text component                                                 //and change its value.
				}
			}
		};

public static IViewPart getView(IWorkbenchWindow window, String viewId) {
    IViewReference[] refs = window.getActivePage().getViewReferences();
    for (IViewReference viewReference : refs) {
        if (viewReference.getId().equals(viewId)) {
            return viewReference.getView(true);
        }
    }
    return null;
}

....
if (event.widget == generateButton) {
IViewPart viewPart = getView(window, viewId);
MyViewPart myViewPart = (MyViewPart)viewPart;
myViewPart.updateText(...);					
}
...

        Button button = new Button(parent, SWT.PUSH);
        button.addSelectionListener(new SelectionAdapter() {

            @Override
            public void widgetSelected(SelectionEvent e) {
                Button button = (Button) e.widget;
                IViewPart findView = PlatformUI.getWorkbench()
                        .getActiveWorkbenchWindow().getActivePage()
                        .findView("Part 2 viewId, which is defined in the plugin.xml");
                if (findView instanceof Part2View) {
                    Part2View part2View = (Part2View) findView;
                    part2View.setText(button.getText());
                }
            }

        });