java写的一个进销存系统，供初学者学习之用。用的知识点有：Java中的MDI窗体,资源文件调用与数据库会话实现,JTable控件与JSpinner 控件的使用,数据有效性验证.-write a java Invoicing system for beginners learning. Point with the knowledge: Java in the MDI form, call the resource file session with the database to achiev