java - 从一个单独的类中调用一个 mutator 方法

Question

我有一个构造函数类:

public class Student
{
    // Declare variables
    public int studentID;
    public String courseName;
    public int courseScore;
    public char courseGrade;

    // Default constructor
    public Student()
    {
       studentID = 1;
       courseName = "CIS 2085";
       courseScore = 89;
    }


    //========================================

    // Constructor with parameters
    public Student(int id, String course, int score)
    {
       setStud(id, course, score);
    }


    //========================================

    public String toString()
    {
       return (studentID + " " + courseName + " " + courseScore);
    }


    //========================================

    public void setStud(int id, String course, int score)
    {
       studentID = id;
       courseName = course;
       courseScore = score;
    }


     //========================================

    public int getStudentID()
    {
       return studentID;
    }


    //========================================

    public String getCourseName()
    {
       return courseName;
    }


    //========================================

    public int getCourseScore()
    {
       return courseScore;
    }


    //========================================

    public char getCourseGrade()
    {
       return courseGrade;
    }


    //========================================

    public static char calculateGrade(int courseScore)
    {
       if (courseScore >= 94)
           courseGrade = 'A';

       else if ((courseScore >= 85) && (courseScore <= 93))
           courseGrade = 'B';

       else if ((courseScore >= 75) && (courseScore <= 84))
           courseGrade = 'C';

       else if ((courseScore >= 65) && (courseScore <= 74))
           courseGrade = 'D';

       else
           courseGrade = 'F';

       return courseGrade;
    }

    //========================================

}

到目前为止，我有我的实现类，如下所示:

import java.util.*;

public class StudentImplementation
{
    // Sllow 'console' to receive input from the user
    static Scanner console = new Scanner(System.in);

    // Method main
    public static void main(String[] args)
    {
        // Declare variables

        // Object 1: first. Uses the default constructor.
        Student first = new Student();

        //System.out.println(first);

        // Object 2: second.
        Student second = new Student(3, "Advanced Java Programming", 83);

        //System.out.println(second);

        // Use calculateGrade method to receive grade for object 1

        char grade = Student.calculateGrade(first.getCourseScore);
        System.out.println(grade);
    }
}

所以我尝试使用我的 calculateGrade 方法根据我的对象 courseScore 输出适当的成绩。

Student 类与我的实现类位于不同的文件中。

当我运行这个程序时，我收到错误:

Exception in thread "main" java.lang.NoSuchMethodError: Student.calculateGrade(I)C
    at StudentImplementation.main(StudentImplementation.java:27)

Answer 1

这是您的 Student 类的一个更清晰的版本，可以执行您希望它执行的操作。我已经删除了不需要的变量和方法，并稍微清理了一下。

我这样做的原因是因为现在，您的代码包含很多没有意义的东西(例如，向方法添加参数，以便您可以在方法本身中设置参数值，然后返回它，在构造函数中使用 setter 方法)。

public class Student {
    public int studentID;
    public String courseName;
    public int courseScore;

    public Student() {
        this(1, "CIS 2085", 89);
    }

    public Student(int id, String course, int score) {
        this.studentID = id;
        this.courseName = course;
        this.courseScore = score;
    }

    @Override
    public String toString() {
        return studentID + " " + courseName + " " + courseScore;
    }

    public int getStudentID() {
        return studentID;
    }

    public String getCourseName() {
        return courseName;
    }

    public int getCourseScore() {
        return courseScore;
    }


    public char getCourseGrade() {
        if (courseScore >= 94) {
            return 'A';
        } else if (courseScore >= 85 && courseScore <= 93) {
            return 'B';
        } else if (courseScore >= 75 && courseScore <= 84) {
            return 'C';
        } else if (courseScore >= 65 && courseScore <= 74) {
            return 'D';
        }
        return 'E';
    }

}

下面是一个示例实现:

public class StudentImplementation {

    public static void main(String[] args) {
        Student first = new Student(); //default constructor
        System.out.println(first.getCourseGrade());
        Student second = new Student(3, "Advanced JAVA Programming", 83);
        System.out.println(second.getCourseGrade());
    }

}