while循环累加器在java中

Question

我正在尝试使用带有未知条目集的while循环制作GPA计算器。当只输入一组信息时，我的程序运行正常。如果我输入多个班级的信息，总数不会更新，我无法弄清楚原因。有任何想法吗？

    import javax.swing.JOptionPane;

    public class GUITestClient {
    public static void main(String[] args) {

    StudentInfo student = new StudentInfo();
    double credits = 0;
    double gradePoints = 0;
    double gradePointsTot = 0;
    double gpa = 0;
    String addAnotherClass = null;



    String name = JOptionPane.showInputDialog("Please enter your name:");
    student.setName(name);

    do{ 

        credits = Double.parseDouble(JOptionPane.showInputDialog("Please
        enter the credits:"));
        student.setCredits(credits);


        String grade = JOptionPane.showInputDialog("Please enter your
        grade:");
        student.setGrade(grade);

        addAnotherClass = JOptionPane.showInputDialog("Press "+"Y"+" to
        enter More class information");

        gradePoints = StudentInfo.addClass(gradePoints, grade);
        gradePointsTot += gradePoints;

    }while(addAnotherClass.equalsIgnoreCase("y"));

    //after loop
    student.setGradePoints(gradePointsTot);
    StudentInfo.getGPA(credits, gpa, gradePointsTot);
    student.setGpa(gpa);


    JOptionPane.showMessageDialog(null,
    student.displayStudentInformation());      


    } 
    }

    class StudentInfo {
    private String  name;
    private double  totalGradePoints;
    private double  credits;
    private String  grade;
    private double  gpa;

    public StudentInfo(){
        setGrade(null);
        setCredits(0);
        setGradePoints(0);
    }
    public StudentInfo(double credits, double totalGradePoints, String
    grade){
        setGrade(grade);
        setCredits(credits);
        setGradePoints(totalGradePoints);
    }

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    public String getGrade() {
        return grade;
    }
    public void setGrade(String grade) {
        this.grade = grade;
    }
    public double getCredits() {
        return credits;
    }
    public void setCredits(double credits) {
        this.credits = credits;
    }

    public double getGradePoints() {
        return totalGradePoints;
    }
    public void setGradePoints(double totalGradePoints) {
        this.totalGradePoints = totalGradePoints;
    }

    public double getGpa() {
        return gpa;
    }
    public void setGpa(double gpa) {
        this.gpa = gpa;
    }

    public static double addClass(double totalGradePoints, String grade){
    double gradePoints = 0;
    double accumGradePoints;

    if(grade.equalsIgnoreCase("A")){
        gradePoints = 4.0;
    }else if(grade.equalsIgnoreCase("B")){
        gradePoints = 3.0;
    } else if(grade.equalsIgnoreCase("C")){
        gradePoints = 2.0;
    } else if(grade.equalsIgnoreCase("D")){
        gradePoints = 1.0;}
    totalGradePoints += gradePoints;

         return totalGradePoints;
    }

    public static double getGPA(double totalGradePoints, double credits,
    double gpa){

        gpa = (credits * totalGradePoints)/ credits);
        return gpa;
    }

    public String displayStudentInformation(){
        String output = "";

        output = output + "Name: " + this.getName() + "\n";
        output = output + "Total Credits: " + this.getCredits() + "\n";
        output = output + "Your grade is: " + this.getGrade() + "\n";
        output = output + "Your GPA is:
        " + this.getGPA(totalGradePoints, credits, gpa) +  "\n";
        output = output + "Press any key to continue!" + "\n";
        output = output + "gp" + totalGradePoints + "credits" + credits;


        return output;
    }
    }