如何获得我的学生成绩计算器程序中类似成绩字母的总数

Question

My program calculates the grades of 30 students with six different scores then displays the letter grades for each student. I have done this already but my problem is how to count the number of A's, B's,C's,D's and F's.

I want my output to be like this:

The number of A's is:

The number of B's is:

The number of C's is:

The number of D's is:

The number of F's is:

import javax.swing.*;
import java.awt.*;
import java.io.*;
import java.util.Scanner;

public class FinalGrade extends JPanel
{
        public static String firstName[]= new String[30];
        public static String lastName[] = new String[30];
        public static String grade[]=new String[30];
        public static int HW1;
        public static int HW2;
        public static int HW3;
        public static int Project;
        public static int Midterm;
        public static int Final;
        public static double Avg_homework;
        public static double Avg_exam;
        public static double Final_numeric_grade;


     public FinalGrade()
     {
     super(new GridLayout(1,0));

     String[] columnNames = {"First Name", "Last Name", "Final Grade"};

     Object[][] data = {
     {firstName[0], lastName[0], grade[0]},
     {firstName[1], lastName[1], grade[1]},
     {firstName[2], lastName[2], grade[2]},
     {firstName[3], lastName[3], grade[3]},
     {firstName[4], lastName[4], grade[4]},
     {firstName[5], lastName[5], grade[5]},
     {firstName[6], lastName[6], grade[6]},
     {firstName[7], lastName[7], grade[7]},
     {firstName[8], lastName[8], grade[8]},
     {firstName[9], lastName[9], grade[9]},
     {firstName[10], lastName[10], grade[10]},
     {firstName[11], lastName[11], grade[11]},
     {firstName[12], lastName[12], grade[12]},
     {firstName[13], lastName[13], grade[13]},
     {firstName[14], lastName[14], grade[14]},
     {firstName[15], lastName[15], grade[15]},
     {firstName[16], lastName[16], grade[16]},
     {firstName[17], lastName[17], grade[17]},
     {firstName[18], lastName[18], grade[18]},
     {firstName[19], lastName[19], grade[19]},
     {firstName[20], lastName[20], grade[20]},
     {firstName[21], lastName[21], grade[21]},
     {firstName[22], lastName[22], grade[22]},
     {firstName[23], lastName[23], grade[23]},
     {firstName[24], lastName[24], grade[24]},
     {firstName[25], lastName[25], grade[25]},
     {firstName[26], lastName[26], grade[26]},
     {firstName[27], lastName[27], grade[27]},
     {firstName[28], lastName[28], grade[28]},
     {firstName[29], lastName[29], grade[29]}
      };

     final JTable table = new JTable(data, columnNames);

     table.setPreferredScrollableViewportSize(new Dimension(300,400));

     table.setFillsViewportHeight(true);

     JScrollPane scrollPane = new JScrollPane(table);
     add(scrollPane);
     }

      private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("Grade Display");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Create and set up the content pane.
        FinalGrade newContentPane = new FinalGrade();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) throws FileNotFoundException
    {
        Scanner input = new Scanner (new File ("student_grades_input.txt"));

        int count = 0;
        while (input.hasNext())
        {
            firstName[count] = input.next();
            lastName[count] =  input.next();
            HW1 = input.nextInt();
            HW2 = input.nextInt();
            HW3 = input. nextInt();
            Project = input.nextInt();
            Midterm = input.nextInt();
            Final = input.nextInt();


            Avg_homework = (HW1 + HW2 + HW3)/3;

            Avg_exam = (Midterm + Final)/2;


            Final_numeric_grade = 0.45 * Avg_homework + 0.25 * Project + 0.30 * Avg_exam ;

            if (Final_numeric_grade > 89)

                  grade[count] = "A";


           else if (Final_numeric_grade > 79 && Final_numeric_grade < 90)

                  grade[count] = "B";



          else if (Final_numeric_grade > 69 && Final_numeric_grade < 80)

                  grade[count] = "C";


          else if (Final_numeric_grade > 59 && Final_numeric_grade < 70)

             grade[count] = "D";


            else

             grade[count] = "F";


            count++;
            }

        input.close();
        createAndShowGUI();                


    }

}

Answer 1

You can use an array to store the counts of the grades where the first index would be "A", the second index would be "B". etc. You can even do this when you set your grade array. Something like this should do the trick:

int[] gradeCount = new int[5]; //Define before your while (input.hasNext())
...
if (Final_numeric_grade > 89){
    grade[count] = "A";
    gradeCount[0]++;}
else if (Final_numeric_grade > 79 && Final_numeric_grade < 90){
    grade[count] = "B";
    gradeCount[1]++;}
else if (Final_numeric_grade > 69 && Final_numeric_grade < 80){
    grade[count] = "C";
    gradeCount[2]++;}
else if (Final_numeric_grade > 59 && Final_numeric_grade < 70){
    grade[count] = "D";
    gradeCount[3]++;}
else{
    grade[count] = "F";
    gradeCount[4]++;}

Then when you need to access the grade counts do something like this:

System.out.println("Number of A: " + gradeCount[0]);
System.out.println("Number of B: " + gradeCount[1]);
System.out.println("Number of C: " + gradeCount[2]);
System.out.println("Number of D: " + gradeCount[3]);
System.out.println("Number of F: " + gradeCount[4]);

Answer 2

All you have to do is iterate over grade array after you have set all your grades and have 6 counters (1 for each letter):

int numberOfA = 0;
int numberOfB = 0;
int numberOfC = 0;
int numberOfD = 0;
int numberOfE = 0;
int numberOfF = 0;
for (int i = 0; i < grade.length; i++) {
    if (grade[i].equals("A")) {
        numberOfA++;
    } else if (grade[i].equals("B")) {
        numberOfB++;
    } else if (grade[i].equals("C")) {
        numberOfC++;
    } else if (grade[i].equals("D")) {
        numberOfD++;
    } else if (grade[i].equals("E")) {
        numberOfE++;
    } else {
        numberOfF++;
    }
}

Then simply print or do whatever you need to do with the counters:

System.out.println("Number of A: " + numberOfA);
System.out.println("Number of B: " + numberOfB);
System.out.println("Number of C: " + numberOfC);
System.out.println("Number of D: " + numberOfD);
System.out.println("Number of E: " + numberOfE);
System.out.println("Number of F: " + numberOfF);

Also please follow Java naming conventions

Except for variables, all instance, class, and class constants are in mixed case with a lowercase first letter. Internal words start with capital letters. Variable names should not start with underscore _ or dollar sign $ characters, even though both are allowed.

From the above: Variable names should start with lower case while classes names should start with an upper case

---

Edit

Also as @Gonzo stated you can use the counters on the code you already have, this will improve performance because you won't be iterating twice on the same array, you can do it as:

if (Final_numeric_grade > 89) { //Be sure to add curly brackets
    grade[count] = "A";
    numberOfA++;
} //And close them
else if (Final_numeric_grade > 79 && Final_numeric_grade < 90) {
    grade[count] = "B";
    numberOfB++;
} 
//And so on ...

And print them as I said above. Just be sure to initialize your variables before incrementing them :)

Answer 3

There can be so many ways to do that. One simple way can be defining counter variables for each grade and increment them in your while loop, when you are determining the grade. Something like :

int gradeACounter=0, gradeBCounter=0;

 if (Final_numeric_grade > 89){

              grade[count] = "A";
              gradeACounter++;
 }

       else if (Final_numeric_grade > 79 && Final_numeric_grade < 90){

              grade[count] = "B";
              gradeBCounter++;
}