我正在为学校做一个项目，要求我为一所学校建立一个等级体系，我很难理解为什么当我有一个公共变量类时，不允许在另一个类的方法中调用它们。有人能举个例子或解释一下这是怎么回事吗？

public void AddEngGrade(Grades obj)
{
Scanner sc1 = new Scanner(System.in);

System.out.println("Which Grade would you like to enter");
System.out.println("");
System.out.println("Major");
System.out.println("Minor");
System.out.println("Other");
System.out.println("");

String gr = sc1.nextLine();

if(gr.equals("Major"))
{
  System.out.print("Please enter the grade here - ");
  obj.EngMajor = sc1.nextInt();
  obj.EngMajPoints += obj.EngMajor;
  obj.EngMajorTot++;
  obj.EngMajAvg = (obj.EngMajPoints/2)*(.6);
}

包含变量的类如下所示

import java.util.*;
public class Grades
{
public int EngMajor = 0;
public int EngMinor = 0;
public int EngOther = 0;
public int EngMajorTot = 0;
public int EngMinorTot = 0;
public int EngOtherTot = 0;
public double EngMajAvg = 0;
public double EngMinAvg = 0;
public double EngOtAvg = 0;
public int EngMajPoints = 0;
public int EngMinPoints = 0;
public int EngOtPoints = 0;
}