Question

好的，基本上这是我关于学生和学生的课程。学生团体; 每个学生都有姓名，身份证和分数/分; 该程序工作正常，但缺少的是StudentGroup类中的SUM函数需要静态并且取一个＆＃34; Group＆＃34;的参数。其中你需要点数之和。我的问题是，当我将函数和ArrayList置于静态时，该函数返回两个组合得分并且我不知道如何使其工作

//程序正常工作并返回正确的值一切;我只是在尝试更改时才会收到这些错误 sumOfPoints函数为静态

我拥有的两个文件是：第1组：

61662126 Laurel 50
61662213马克35.5
61662345 Yanny 67
61662127拉里27
61662125 Kevin 87.5

和第2组：

61662126 Jason 70

61662213 Josh 25.5

61662345 Bobby 57

61662127 Megan 17

61662125德雷克86.5

正确的输出应该是：第1组总分：267.0

第2组总分：256.0

将Group1与Group2进行比较：1

但是当我把它放到静态时它会返回两者中的523，这两个组合在一起并且我不明白我做错了什么

public interface IFile
{
    public void Load();
}





public class Student implements Comparable<Student> 
{

    private int facnum;
    private String name;
    private double points;

    public Student(int fn, String n, double p)
    {
        this.facnum = fn;
        this.name = n;
        this.points = p;
    }

    public void SetFN(int fn)
    {
        this.facnum = fn;
    }

    public void SetName(String n)
    {
        this.name = n;
    }

    public void SetPoints(double p)
    {
        this.points = p;
    }

    public int GetFN()
    {
        return this.facnum;
    }

    public String GetName()
    {
        return this.name;
    }

    public double GetPoints()
    {
        return this.points;
    }

        public boolean equals(Object s)
{
    if (this.GetFN() != ((Student)s).GetFN())
    {
        return false;
    }
        return true;
}

public int compareTo(Object s) 
{
    if(this.GetFN() < ((Student)s).GetFN())
    {
        return -1;
    }
    if(this.GetFN() > ((Student)s).GetFN())
    {
        return 1;
    }
    return 0;
}


    public String toString()
    {
        return "Faculty Number: " + this.facnum + " Name: " + this.name + " Points: " + this.points + " \n";
    }
}




import java.io.*;
import java.util.*;

public class StudentsGroup implements IFile, Comparable<Object>
{
    private String groupname;
    private List<Student>oStudent = new ArrayList<Student>();

    public StudentsGroup(String filename)
    {
        this.groupname = filename;
        Load();
    }

    public void Load(){
        try 
        {   
            Scanner sc=new Scanner(new File(this.groupname));
            while(sc.hasNextLine())
            {
                oStudent.add(new Student(sc.nextInt(),sc.next(),
                        sc.nextDouble()));
            }
        sc.close();
        }
        catch(IOException e)
        {
            System.out.println("Input/Output Error...");
        }
    }


    public void printColl()
    {
        System.out.println(oStudent.toString());
    }

    public  List<Student> sortedListFN()
    {
        Collections.sort(oStudent);
        return oStudent;
    }

    public double sumOfPoints()
    {
        double sum = 0.00;

        for(Iterator<Student> it= oStudent.iterator(); it.hasNext();)
        {
            Student c = it.next();
            sum += c.GetPoints();
        }
        return sum;
    }

    public int compareTo(Object s) 
    {
        if(this.sumOfPoints() < ((StudentsGroup) s).sumOfPoints())
        {
            return -1;
        }
        if(this.sumOfPoints() > ((StudentsGroup) s).sumOfPoints())
        {
            return 1;
        }
        return 0;
    }


    public static void main(String[] args)
    {
        StudentsGroup oGroup1 = new StudentsGroup("Group1.txt");
        oGroup1.printColl();
        System.out.println("Sorted order by FN: " + oGroup1.sortedListFN() + "\n");
        StudentsGroup oGroup2 = new StudentsGroup("Group2.txt");
        System.out.println("Total points of Group1: " + oGroup1.sumOfPoints() + "\n");
        System.out.println("Total points of Group2: " + oGroup2.sumOfPoints() + "\n");
        System.out.println("Comparing Group1 to Group2: " + oGroup1.compareTo(oGroup2));

    }


}

编辑//我尝试的静态方法是将oStudent更改为static：

private static List<Student>oStudent = new ArrayList<Student>();

显然将sum函数改为static＆amp;编辑compareTo方法：

public static double sumOfPoints(Object s)
    {
        double sum = 0.00;
        s  = new ArrayList<Student>(oStudent);

        for(Iterator<Student> it= ((List<Student>) s).iterator(); it.hasNext();)
        {
            Student c = it.next();
            sum += c.GetPoints();
        }
        return sum;
    }

    public int compareTo(Object s) 
    {
        if(this.sumOfPoints(this) < ((StudentsGroup) s).sumOfPoints(s))
        {
            return -1;
        }
        if(this.sumOfPoints(this) > ((StudentsGroup) s).sumOfPoints(s))
        {
            return 1;
        }
        return 0;
    }

和输出：

System.out.println("Total points of Group1: " + oGroup1.sumOfPoints(oGroup1) + "\n");
        System.out.println("Total points of Group2: " + oGroup2.sumOfPoints(oGroup2) + "\n");
        System.out.println("Comparing Group1 to Group2: " + oGroup1.compareTo(oGroup2));

and the output starts returning 523

Answer 1

您的静态方法会使用该特定实例类的内部对象覆盖s：

s  = new ArrayList<Student>(oStudent);

我认为你的错误就在这里。这不是你如何使用类的静态方法。正确的方法是StudentsGroup.sumOfPoints(yourObjectHere)。静态方法不应该知道特定实例的任何字段。

sum＆amp;的静态函数的compareTo

1 个答案: