问GPA阵列计算误差

EN

import java.util.*;

public class Gpa{

      int[] credits = new int[4];
      String[] grades = new String[4];

      private int numCourses;
      private int maxCourses;
      private int sumOfCourses;
      private int sumCredits;
      private int sumPoints;
      int newCredits;
      int totalSum = 0;
      int total = 0;


      public Gpa(int noCourses){
        maxCourses = noCourses;
        numCourses = 0; 


      }

      public void addCourse(int _newCredits, String newGrade){
         for (int i=0; i<maxCourses; i++){
           newCredits = _newCredits;
           credits[i] = newCredits;
         }
         for (int i=0; i<maxCourses; i++){
            grades[i] = newGrade;
         }
            switch (newGrade) {
               case "A":
               case "a":
                  newGrade = "4";
                  break;
               case "B":
               case "b":
                  newGrade = "3";
                  break;
               case "C":
               case "c":
                  newGrade = "2";
                  break;
               case "D":
               case "d":
                  newGrade = "1";
                  break;
               case "F":
               case "f":
                  newGrade = "0";
                  break;
              }
          sumPoints = sumPoints + (newCredits * Integer.parseInt(newGrade));
          numCourses++;

      }

      public double calcGPA(){
         for (int i=0; i<maxCourses; i++){
            sumCredits = sumCredits + newCredits;
         }
         double gpa = (double)sumPoints/sumCredits;
         return gpa;
      }


















} // end class

import java.util.Scanner;

public class GpaTestEx2
{

    public static void main (String[] args)
    {
        //declarations
        Scanner in = new Scanner(System.in); //input object
        int numCourses; //number of courses - can be changed
        int credits;        //number of credits for a course
        String grade;       //grade for course


        //read in number of courses
        System.out.print("Enter number of courses: ");
        numCourses = in.nextInt();

        //create Gpa object to hold specified number of courses
        Gpa myGPA = new Gpa(numCourses);

        //read in all courses and add course information to Gpa object
        for (int k=0; k<numCourses; k++)
        {
            System.out.print("Enter credits for course " + (k+1) + ": ");
            credits = in.nextInt();
            System.out.print("Enter grade for course " + (k+1) + ": ");
            grade = in.next();

            myGPA.addCourse(credits, grade);
        }

        //print results
        System.out.println();
        System.out.printf("GPA is %4.2f%n", myGPA.calcGPA( )); 

    } //end main
}