Question

我的总数不会更新。每次执行代码时，gpa都会显示0.0。我添加了＆＃34; gp＆＃34;查看输入用户信息时是否会更新＆＃34;成绩点，但不会。任何帮助都会很棒！我看了看其他问题，似乎无法解决我的问题！

import javax.swing.JOptionPane;

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

        StudentInfo student = new StudentInfo();
        double credits;
        String name = JOptionPane.showInputDialog("Please enter your name:");
        student.setName(name);
        credits = Double.parseDouble(JOptionPane.showInputDialog("Please enter the credits:"));
        student.setCredits(credits);

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

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

public 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 double addClass(double totalGradePoints, String grade){
        double gradePoints = 0;
        if(grade.equals("A")){
            gradePoints = 4.0;
        }else if(grade.equals("B")){
            gradePoints = 3.0;
        } else if(grade.equals("C")){
            gradePoints = 2.0;
        } else if(grade.equals("D")){
            gradePoints = 1.0;}
        totalGradePoints = (totalGradePoints +gradePoints);

        return getGradePoints();
        }

        public double getGPA(){
            this.setGpa(this.getCredits() / this.getGradePoints());
            return this.getGpa();
        }

        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() +  "\n";
            output = output + "Press any key to continue!" + "\n";
            output = output + "gp" + totalGradePoints + "\n";

            return output;
        }
}

Answer 1

    public double addClass(double totalGradePoints, String grade){
    double gradePoints = 0;
    if(grade.equals("A")){
        gradePoints = 4.0;
    }else if(grade.equals("B")){
        gradePoints = 3.0;
    } else if(grade.equals("C")){
        gradePoints = 2.0;
    } else if(grade.equals("D")){
        gradePoints = 1.0;}

    totalGradePoints = (totalGradePoints +gradePoints);
}

问题出现在addClass的最终陈述中。 Java是按值传递，这意味着此处可见的totalGradePoints是addClass方法中的局部变量，包含 副本< / em> 您调用addClass时传递的任何值。您对该值所做的任何更新仅影响本地副本，而不影响原始变量。

方法签名不需要totalGradePoints参数。它应该是

public double addClass(String grade) { ...

您需要将本地gradePoints添加到班级＆＃39;成员变量totalGradePoints。

Answer 2

问题在于你的this.getGradePoints（）。它不是值的getter，并且您没有在StudentInfo student = new StudentInfo（）中为学生的同一对象实例设置函数内部的值; 您必须在该对象上设置所有setter变量＆＃39; student＆＃39;你创造了。

试试这个：

package guitestclient;

import javax.swing.JOptionPane;

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

        StudentInfo student = new StudentInfo();
        double credits;
        double gradePoints = 0;
        double gradePointsTot = 0;
        double gpa = 0;
        int classCount = 0;


        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);

        //calculates gpa value for grade
        gradePoints = StudentInfo.addClass(gradePoints, grade);
        gradePointsTot += gradePoints;
        classCount++;
     } while (classCount < 5);    

        //after loop
        student.setGradePoints(gradePointsTot);
        gpa = StudentInfo.getGPA(credits, gpa, classCount);
        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;
        if(grade.equals("A")){
            gradePoints = 4.0;
        }else if(grade.equals("B")){
            gradePoints = 3.0;
        } else if(grade.equals("C")){
            gradePoints = 2.0;
        } else if(grade.equals("D")){
            gradePoints = 1.0;}
        totalGradePoints = (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() +  "\n";
            output = output + "Press any key to continue!" + "\n";
            output = output + "gp" + this.getGradePoints() + "\n";

            return output;z
        }
}

Answer 3

在你的addClass方法中，你有totalGradePoints作为局部变量。

public double addClass(double totalGradePoints, String grade)

您应该使用全局变量totalGradePoints而不是本地变量。因此，删除该变量，使方法看起来像

public double addClass(String grade)

但我没有看到你调用addClass方法的任何地方。

Java GPA CALC问题

3 个答案: