从单独的类中调用mutator方法

Question

I have a constructor class as so:

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;
    }

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

}

And I have my implementation class so far, like this:

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);
    }
}

So I am trying to use my calculateGrade method to output the appropriate grade based on my objects courseScore.

The Student class is in a separate file from my implementation class.

When I run this program I receive the error:

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

Answer 1

Change your calculateGrade method to:

public char calculateGrade() {
    courseScore = this.getCourseScore(); // This refers to the student
                                         // from whom you called the
                                         // calculaGrade() method -->
                                         // first.calculateGrade()
    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;
}

Then just use first.calculateGrade(). And print the result:

Student first = new Student();
char firstStudentGrade = first.calculateGrade();
System.out.println(firstStudentGrade);

PS: method names do not start with capital letters ;)

Answer 2

Here's a cleaner version of your Student class that does what you want it to do. I've taken out the unnecessary variables and methods, and cleaned it up a bit.

The reason I did this is because right now, your code contains a lot of things that don't make sense (eg. adding a parameter to a method so you can set the parameters value in the method itself and then return it, using a setter method in your constructor).

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';
    }

}

Here's an example implementation to go along with that:

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());
    }

}

Answer 3

Use:

public char CalculateGrade()
{
    if (this.courseScore >= 94)
        courseGrade = 'A';

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

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

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

    else
        courseGrade = 'F';

    g = courseGrade;

    return g;
}

And call it as:

System.out.println(first.CalculateGrade());

Answer 4

After creating your Student object, simply call your method...

Student first = new Student();
first.CalculateGrade();

And remove the g parameter from CalculateGrade(char gg) . You don't need it.

Answer 5

Change the statement

char grade = Student.calculateGrade(first.getCourseScore);

to

char grade = Student.calculateGrade(first.getCourseScore());

You missed the () during the method call.