import java.util.Scanner;
class StatisticsCalculator
{
    private double n1,n2,n3,n4,n5;
    Scanner scanner;
    public StatisticsCalculator()
    {
       Scanner Kb = new Scanner(System.in);
       System.out.println("Enter the cost  on Monday:");
       double n1 = Kb.nextDouble();
       System.out.println("Enter the cost  on Tuesday:");
       double n2 = Kb.nextDouble();
       System.out.println("Enter the cost  on Wednesday:");
       double n3 =Kb.nextDouble();
       System.out.println("Enter the cost  on Thursday:");
       double n4 = Kb.nextDouble();
       System.out.println("Enter the cost  on Friday:");
       double n5 = Kb.nextDouble();
    }
    public void setCost(double n1,double n2,double n3,double n4,double n5)
    {    
    }
    public double getCost()
    {
       List list = new ArrayList();
       list.add(n1);
       list.add(n2);
       list.add(n3);
       list.add(n4);
       list.add(n5);
       return list;
    }
};
public class TestStatisticsCalculator
{
    public static void main(String[] args)
    {
       TestStatisticsCalculator a=new TestStatisticsCalculator();
       a.sum();
       a.average();
       System.out.println("the cost of total fuel is: "+total);
       System.out.println("the cost of average fuel is:"+ mean);
    }
    public static void sum()
    {
        total=n1+n2+n3+n4+n5;
        return total;
    }
    public static void average()
    {
        mean=(n1+n2+n3+n4+n5)/5;
        return mean;
    }
}

其实就是要求输入五个数字 求平均值和总数。 但是我只会最简单的，不会这个样子的编程。
应该有两个错误，一个是class里面 return和list不知道怎么使用。 第二是public class 无法使用class里面的n1n2n3n4n5
求助这个程序应该怎样改才是正确的

怎样改变，让这个程序变成class{}；public class{}的形式呢？class里面储存5个数 publicclass里面计算？ 自己改了很久没有成功，真心求教