for(Object item : combo_container) {
JComboBox box = (JComboBox) item;
box.removeAllItems();
}
But is not really a great idea. Why not array of JComboBox? Like this:
JComboBox<String>[] combo_container = { winners_combo_box, bikes_combo_box,
teams_combo_box, riders_combo_box };
for(JComboBox box : combo_container)
box.removeAllItems();
Of course assuming winners_combo_box, bikes_combo_box etc. are objects of JComboBox class