如何在多类包的主要方法中使用属性？

Question

我是新手。我正在编写一个程序，该程序使用以下信息来计算许多学生的成绩，但我从一开始就卡住了。我在一个包中使用不同的 classes，我只是不知道如何在 main 方法中将它们放在一起。我在写“FirstName = oScan.nextLine();”时收到此消息 "non-static variable FirstName cannot be referenced from a static context Error."在最后几行。我的问题是如何在我的主要方法中使用下面的这些属性名姓作业大道测验大道项目大道测试大道期末成绩字母等级

我是否编写了正确的构造函数、getter 和 setter？

/* 这是第一个class，父class */

package student;

public class Person {



 protected String FirstName, LastName;

    //Constructor
    public Person(String FirstName, String LastName) {
        this.FirstName = FirstName;
        this.LastName = LastName;
    }

    //Getters
 public String getFirstName() {
        return FirstName;
    }

    public String getLastName() {
        return LastName;
    }
    //Setters
    public void setFirstName(String FirstName) {
        this.FirstName = FirstName;
    }

     public void setLastName(String LastName) {
        this.LastName = LastName;
    }


}

这是第二个class

package student;

import java.util.ArrayList;
import java.util.Scanner;


public class Student extends Person{
    private int HomeworkAve, QuizAve, ProjectAve, TestAve; 
    private double FinalGrade;
    private String LetterGrade;

//Constructor for the averages
    public Student(int HomeworkAve, int QuizAve, int ProjectAve, int TestAve, String FirstName, String LastName) 
    {
        super(FirstName, LastName);
        this.HomeworkAve = HomeworkAve;
        this.QuizAve = QuizAve;
        this.ProjectAve = ProjectAve;
        this.TestAve = TestAve;

    }

    //Method to calculate final grade and letter grade
    //Final grade calculation
    public double CalcGrade (int HomeworkAve, int QuizAve, int ProjectAve, int TestAve)
    {
FinalGrade = (double)(0.15*HomeworkAve + 0.05*QuizAve + 0.4 * ProjectAve + 0.4*TestAve);
return FinalGrade;
    }

    //Letter grade calculation
    public String CalcGrade ( double FinalGrade)
    {
        if ( FinalGrade >= 90.00)
        LetterGrade="A";
    else if(FinalGrade >= 80.00)
        LetterGrade="B";
    else if(FinalGrade>=70.00)
        LetterGrade="C";
    else if(FinalGrade>=60.00)
        LetterGrade="D";
    else LetterGrade="F";

        return LetterGrade;
    }



    public Student(int HomeworkAve, int QuizAve, int ProjectAve, int TestAve, double FinalGrade, String LetterGrade, String FirstName, String LastName) {
        super(FirstName, LastName);
        this.HomeworkAve = HomeworkAve;
        this.QuizAve = QuizAve;
        this.ProjectAve = ProjectAve;
        this.TestAve = TestAve;
        this.FinalGrade = FinalGrade;
        this.LetterGrade = LetterGrade;
    }


    //Setters for this student class
    public void setHomeworkAve(int HomeworkAve) {
        this.HomeworkAve = HomeworkAve;
    }

    public void setQuizAve(int QuizAve) {
        this.QuizAve = QuizAve;
    }

    public void setProjectAve(int ProjectAve) {
        this.ProjectAve = ProjectAve;
    }

    public void setTestAve(int TestAve) {
        this.TestAve = TestAve;
    }

    public void setFinalGrade(int FinalGrade) {
        this.FinalGrade = FinalGrade;
    }

    public void setLetterGrade(String LetterGrade) {
        this.LetterGrade = LetterGrade;
    }


    //Getters for this student class
    public int getHomeworkAve() {
        return HomeworkAve;
    }

    public int getQuizAve() {
        return QuizAve;
    }

    public int getProjectAve() {
        return ProjectAve;
    }

    public int getTestAve() {
        return TestAve;
    }

    public double getFinalGrade() {
        return FinalGrade;
    }

    public String getLetterGrade() {
        return LetterGrade;
    }


   public static void main(String[] args){
    Scanner oScan = new Scanner(System.in);
    Scanner iScan = new Scanner(System.in);

   ArrayList<Student> students = new ArrayList<>();



   System.out.println("Enter the number of students");

   int numberOfStudents = iScan.nextInt();

    for(int iCount = 0;iCount < numberOfStudents;){

    System.out.println("Enter the name for Student " + ++iCount);
    System.out.println("Enter First Name");
    String FirstName = oScan.nextLine();
    System.out.println();

    System.out.println("Enter Last Name");
    String LastName = oScan.nextLine();
     System.out.println();

    System.out.println("Enter Homework Average");
    int HomeworkAve = iScan.nextInt();
    System.out.println();

    System.out.println("Enter Quiz Average");
    int QuizAve = iScan.nextInt();
    System.out.println();

    System.out.println("Enter Project Average");
    int ProjectAve = iScan.nextInt();
    System.out.println();

    System.out.println("Enter Test Average");
    int TestAve = iScan.nextInt();
    System.out.println();
    double Fin;



 Student hobbit = new Student(HomeworkAve,QuizAve, ProjectAve,TestAve,FirstName, LastName);
    students.add(hobbit);
  }
}
}

Answer 1

您需要创建 class 的实例才能访问非静态 methods/variables。

这意味着：

Person p = new Person("First Name Here", "Last Name");

这是低效的，所以你应该做的是，

public static void main(String[] args){
   ArrayList<Student> students = new ArrayList<Student>();
   Scanner oScan = new Scanner(System.in);
   System.out.println("Enter the number of students");

   int numberOfStudents = oScan.nextInt();

    for(int i = 0;i < numberOfStudents;i++){
    System.out.println("Enter First Name");
   String fn = oScan.nextLine();
    System.out.println(fn);

    System.out.println("Enter Last Name");
    String ln = oScan.nextLine();
    System.out.println(ln);

   //Add all the score stuff
 Student s = new Student(homeworkAve,quizAve,projectAve, testAve,fn,ln);
    students.add(s);
  }
}

编辑：编辑以包含列表

EDIT2：编辑制作 "Student" 个对象

如何在多类包的主要方法中使用属性？

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