By newButton, if canvas != empty, than would ask if the state should be saved.

src/ui/view/GUI.java

@@ -1305,6 +1305,14 @@ public class GUI<E> implements CategoryListener {
 
 			@Override
 			public void actionPerformed(ActionEvent arg0) {
+				if (model.getObjectsOnCanvas().size() != 0) {
+					int newWarning = JOptionPane.YES_NO_OPTION;
+					int dialogForNewWarning = JOptionPane.showConfirmDialog(null, "Do you want to save the old data?",
+							"Warning", newWarning);
+					if (dialogForNewWarning == JOptionPane.YES_OPTION) {
+						mntmSave.doClick();
+					}
+				}
 				model.getEdgesOnCanvas().removeAll(model.getEdgesOnCanvas());
 				model.getObjectsOnCanvas().removeAll(model.getObjectsOnCanvas());
 				controller.setSelectedObjectID(0);