3．编写一个程序模拟自动售货机。可以通过向售货机中投入硬币来购买商品。用户从售货机商品列表选择某一商品并投入硬币。如果金额足够，则提供相应商品；如果金额不够，或者该商品已售完，则将硬币退回。维护售货机的工作人员可以为其添加商品或者取走售货款项。利用CRC卡片设计类和类中的方法，同时给出UML图并实现该程序-3. Write a program to simulate the vending machine. Can pass to the vending machine into the COINS to buy goods. The user from the vending machine commodity list choose a commodity and put in a coin. If the amount is enough, then to provide corresponding commodities　If the amount is not enough, or the goods have already been sold out, will return COINS. The vending machine maintenance staff to add commodities or take away sales amount. Using CRC card design classes and class of methods, at the same time given UML diagrams and implement the program