说明：  设计一个学生注册界面。输入的信息包括学号（6位数字），姓名（不超过6个汉字），密码（不少于6个字符，不多于8个字符，且需要输入2次，2次输入的密码必须完全相同），专业（从“数学”、“计算机”和“外语”中选择，也可以自行输入），年级（从“一年级”、“二年级”、“三年级”和“四年级”中选择一项，且只能选择一项）。点击“注册”按钮后，程序检查输入是否正确，若错误则显示相应的提示信息，否则弹出一个消息窗口，显示所有输入的注册信息。程序文件命名为Exe9_1.java
(Design a student registration interface. Input information includes student number (6 digits), name (no more than 6 Chinese characters), password (no less than 6 characters, no more than 8 characters, and need to be input twice, the password must be exactly the same for two times), major (selected from "mathematics", "computer" and "foreign language" or self-input), grade (from "first grade", "second grade", "third grade). Choose one of the grades and the fourth grade, and only one of them. After clicking the "Registration" button, the program checks whether the input is correct, and displays the corresponding prompt information if the error occurs. Otherwise, a message window pops up to display all the input registration information. The program file is named Exe9_1. Java)