swing实现的自动售货机，面板功能包括：多种硬币按钮模拟投币，选择商品进行交易，确认取货并找零，取消按钮取回已投硬币。售货机内物品数量以及硬币数量可修改-swing to achieve a vending machine, the panel features include: a variety of simulated coin coin button, select commodities trading, confirm pick up and give change, cancel