学生、大学生、研究生类-2：根据成绩输出等级（基类改为抽象类）

[java]代码库

import java.util.Scanner;
public class Main{
    public static void main(String[] args) {
         Scanner scan = new Scanner(System.in);     
 
         int no = scan.nextInt();
         String name = scan.next();     
         String sex = scan.next();     
         String major = scan.next();
         int grade = scan.nextInt();
         CollegeStudent c = new CollegeStudent(no, name, sex, major,grade);
         c.getGrade();
 
         no = scan.nextInt();
         name = scan.next();     
         sex = scan.next();     
         major = scan.next();
         String supervisor = scan.next();
         grade = scan.nextInt();
         GraduateStudent g = new GraduateStudent(no, name, sex, major, supervisor,grade );
         g.getGrade();
         
         scan.close();
    }
}
abstract class Student
{
    private int num;
    private String name;
    private String sex;
    public int grade;
    public Student(int n, String na, String s, int g)
    {
        num = n;
        name = na;
        sex = s;
        grade = g;
    }
    public int getNum()
    {
        return num;
    }
    public String getName()
    {
        return name;
    }
    public String getSex()
    {
        return sex;
    }
    public abstract void getGrade();
}
class CollegeStudent extends Student
{
    private String major;
    public CollegeStudent(int n, String na, String s, String m,int g)
    {
        super(n,na,s,g);
        major = m;
    }
    public String getMajor()
    {
        return major;
    }
    public void getGrade()
    {
    	if(grade >= 80 && grade <= 100)
    		System.out.println("A");
    	else if (grade >= 70 && grade < 80)
    		System.out.println("B");
    	else if (grade >= 60 && grade < 70)
    		System.out.println("c");
    	else if (grade >= 50 && grade < 60)
    		System.out.println("D");
    	else 
    		System.out.println("E");
    }
}
class GraduateStudent extends CollegeStudent
{
    private String supervisor;
    public GraduateStudent(int n, String na, String s, String m, String su, int g)
    {
        super(n,na,s,m,g);
        supervisor = su;
    }
    public void getGrade()
    {
    	if(grade >= 90 && grade <= 100)
    		System.out.println("A");
    	else if (grade >= 80 && grade < 90)
    		System.out.println("B");
    	else if (grade >= 70 && grade < 80)
    		System.out.println("c");
    	else if (grade >= 60 && grade < 70)
    		System.out.println("D");
    	else 
    		System.out.println("E");
    }
}