用Java编写程序实现以下功能 （1）从键盘输入学生姓名、学号、成绩，并保存到文本文件中，重复进行直到遇到空字符为之。 （2）从文件读取各学生成绩，并计算所有学生成绩的平均值、最大、最小值-The following functions written in Java programs (1) from the keyboard input student name, student number, grades, and saved to a text file, and repeat until a null character to whom. (2) to read from a file for each student achievement, and calculate the average scores of all students, the maximum and minimum