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

import java.util.Scanner;

public class Test {

    static double n1;
    static double n2;
    static double n3;
    static double n4;
    static double n5;

    Scanner scanner;

    public static void main(String[] args) {

        double mean = 0;

        Scanner Kb = new Scanner(System.in);
        System.out.println("Enter the cost  on Monday:");
        n1 = Kb.nextDouble();
        System.out.println("Enter the cost  on Tuesday:");
        n2 = Kb.nextDouble();
        System.out.println("Enter the cost  on Wednesday:");
        n3 = Kb.nextDouble();
        System.out.println("Enter the cost  on Thursday:");
        n4 = Kb.nextDouble();
        System.out.println("Enter the cost  on Friday:");
        n5 = Kb.nextDouble();

        Test a = new Test();
        a.average(mean);
    }

    public double average(double mean) {
        mean = ((n1 + n2 + n3 + n4 + n5) / 5);
        System.out.println("the cost of average fuel is:" + mean);
        return mean;
    }
}

修改了下你的代码，放到eclipse里面一看，很蛋疼啊哥哥，你看看，方法设置为void意味着什么，定义的类型一定要和返回的是一样的，或者泛型。还有优先级的运算要看一下，然后整理下你的代码吧，你照谁敲的，给我敲死他，误人子弟啊。这个坑哦

还有代码格式，你的格式要注意，

import java.util.*;

public class Calculate {
   
    private double n1,n2,n3,n4,n5;
   
    public void go(){
        Scanner sc=new Scanner(System.in);
        System.out.println("请依次输入五个数(数与数中间用enter键分隔)：");
        n1=sc.nextDouble();
        n2=sc.nextDouble();
        n3=sc.nextDouble();
        n4=sc.nextDouble();
        n5=sc.nextDouble();
    }
   
    public static void main(String[] args){
        
        Calculate ca=new Calculate();
        ca.go();
        System.out.println("平均值为："+ca.average());
        System.out.println("和为："+ca.sum());
        
    }
   
    public double average(){
        double mean=(n1+n2+n3+n4+n5)/5;
        return mean;
    }
    public double sum(){
        double sum=n1+n2+n3+n4+n5;
        return sum;
    }

}

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

好好去理解“面向对象”的概念吧。

看一下嵌套类，

这个可以i结贴了