Void Methods and Value Returning Methods in Java

Question

Hello,
I'm new here so please let me know if I overstep any of the rules or expectations. I merely want to learn more about Java Programming efficiently, and easily. I can ask and discuss these topics with my online prof, but she doesn't have much time.
So right now I'm trying to solve a problem. It's a typical college level computing problem which I've already turned in. So I'm not looking for someone to do my homework for me or something. It's just that the program didn't work. Even though I probably won't get a very good grade for it, I want to
make it work! I'm kind of slow when it comes to java so just bear with me.
The prof wanted us to write an algorithm that reads a student's name and 6 exam scores. Then it computes the average score for each student, assigns a letter grade, using a rating scale:
90 and above = A
80 - 89 = B
70 ? 79 = C
60 - 69 = D
Less then 60 ? F
We had to use a void method to determine the average score for each student, a loop inside the method to read the and sum the 6 scores but without outputting the average score. The sum and average had to be returned in and output in void main.
Then we had to use a value-returning method CalculateGrade to determine and return the grade for each student. But it can't output the grade because that must be done in void main.
Finally the class average must be output.
Our prof gave us a list of student names with their 6 scores.
Ward 100 54 98 65 35 100
Burris 89 65 87 84 15 32
Harris 54 21 55 87 70 54
Bettis 43 55 68 54 15 25
Staley 87 54 98 45 54 56
Randle 54 87 54 98 65 15
Maddox 56 14 40 50 40 50
Roth 30 40 54 78 24 19
Holmes 14 87 98 34 55 57
So all the data had to be read from a file and the results output to a file. Also we couldn't use 'global variables'. We had to use the appropriate parameters to pass values to and from methods.
Question 1:  What does she mean by 'no global variables'? Maybe she means: don't use "*double test1, test2, test3, test4, test5*;"
Anyway because I'm a slow learner with Java, I end up looking for sample programs that seem to do a similar job as the problem posed. So with this program I decided to adapt a program called Comparison of Class Averages.
//Program: Comparison of Class Averages.
import java.io.*;
import java.util.*;
import java.text.DecimalFormat;
public class DataComparison
public static void main (String[] args) throws
FileNotFoundException, IOException
//Step 1
String courseId1; //course ID for group 1
String courseId2; //course ID for group 2
int numberOfCourses;
DoubleClass avg1 = new DoubleClass(); //average for a course
//in group 1
DoubleClass avg2 = new DoubleClass(); //average for a course
//in group 2
double avgGroup1; //average group 1
double avgGroup2; //average group 2
String inputGroup1;
String inputGroup2;
StringTokenizer tokenizer1 = null;
StringTokenizer tokenizer2 = null;
//Step 2 Open input and output files
BufferedReader group1 =
new BufferedReader(new FileReader("a:\\group1.txt"));
BufferedReader group2 =
new BufferedReader(new FileReader("a:\\group2.txt"));
PrintWriter outfile =
new PrintWriter(new FileWriter("a:\\student.out"));
DecimalFormat twoDecimal =
new DecimalFormat("0.00"); //Step 3
avgGroup1 = 0.0; //Step 4
avgGroup2 = 0.0; //Step 5
numberOfCourses = 0; //Step 6
//print heading: Step 7
outfile.println("Course No Group No Course Average");
inputGroup1 = group1.readLine(); //Step 8
inputGroup2 = group2.readLine(); //Step 9
while((inputGroup1 != null) &&
(inputGroup2 != null)) //Step 10
tokenizer1 = new StringTokenizer(inputGroup1);
courseId1 = tokenizer1.nextToken(); //Step 10a
tokenizer2 = new StringTokenizer(inputGroup2);
courseId2 = tokenizer2.nextToken(); //Step 10b
if(!courseId1.equals(courseId2)) //Step 10c
System.out.println("Data error: Course IDs "
+ "do not match.");
System.out.println("Program terminates.");
outfile.println("Data error: Course IDs "
+ "do not match.");
outfile.println("Program terminates.");
outfile.close();
return;
else //Step 10d
calculateAverage(group1, tokenizer1, avg1); //Step 10d.i
calculateAverage(group2, tokenizer2, avg2); //Step 10d.ii
printResult(outfile,courseId1,1,avg1); //Step 10d.iii
printResult(outfile,courseId2,2,avg2); //Step 10d.iv
avgGroup1 = avgGroup1 + avg1.getNum(); //Step 10d.v
avgGroup2 = avgGroup2 + avg2.getNum(); //Step 10d.vi
outfile.println();
numberOfCourses++; //Step 10d.vii
inputGroup1 = group1.readLine(); //Step 10e
inputGroup2 = group2.readLine(); //Step 10f
}//end while
if((inputGroup1 != null) && (inputGroup2 == null)) //Step 11a
System.out.println("Ran out of data for group 2 "
+ "before group 1.");
else //Step 11b
if((inputGroup1 == null) && (inputGroup1 != null))
System.out.println("Ran out of data for "
+ "group 1 before group 2.");
else //Step 11c
outfile.println("Avg for group 1: " +
twoDecimal.format(avgGroup1 / numberOfCourses));
outfile.println("Avg for group 2: " +
twoDecimal.format(avgGroup2 / numberOfCourses));
outfile.close(); //Step 12
public static void calculateAverage(BufferedReader inp,
StringTokenizer tok,
DoubleClass courseAvg)
throws IOException
double totalScore = 0.0;
int numberOfStudents = 0;
int score = 0;
if(!tok.hasMoreTokens())
tok = new StringTokenizer(inp.readLine());
score = Integer.parseInt(tok.nextToken());
while(score != -999)
totalScore = totalScore + score;
numberOfStudents++;
if(!tok.hasMoreTokens())
tok = new StringTokenizer(inp.readLine());
score = Integer.parseInt(tok.nextToken());
}//end while
courseAvg.setNum(totalScore / numberOfStudents);
}//end calculate Average
public static void printResult(PrintWriter outp,
String courseId,
int groupNo, DoubleClass avg)
DecimalFormat twoDecimal =
new DecimalFormat("0.00");
if(groupNo == 1)
outp.print(" " + courseId + " ");
else
outp.print(" ");
outp.println("\t" + groupNo + "\t "
+ twoDecimal.format(avg.getNum()));
So my adaptation turned out like this:
//Program: Compute individual and class averages from input file.
import java.io.*;
import java.util.*;
public class Exams
public static void main (String[] args)
throws FileNotFoundException
//Step 1
String nameId; //student name ID for list
int numberOfStudents;
DoubleClass avg = new DoubleClass(); //average for a student
//in list
double avgList; //average for list
//Step 2 Open the input and output files
Scanner group1 = new Scanner(new FileReader("c:\\list.txt"));
PrintWriter outfile = new PrintWriter("c:\\student.out");
avgList = 0.0; //Step 3
numberOfStudents = 0; //Step 5
//print heading: Step 6
outfile.println("NameID List Student Average");
calculateAverage(list, avg); //Step 7d.i
printResult(outfile,nameID, avg); //Step 7d.iii
avgList = avgList + avgList.getNum(); //Step 7d.v
outfile.println();
numberOfStudents++; //Step 7d.vii
outfile.printf("Avg for List: %.2f %n",
(avgList / numberOfStudents));
public static void calculateAverage(Scanner inp,
DoubleClass courseAvg)
double totalScore = 0.0;
int numberOfStudents = 0;
int score = 0;
score = inp.nextInt();
courseAvg.setNum(totalScore / numberOfStudents);
}//end calculate Average
public static void printResult(PrintWriter outp,
String nameId,
int groupNo, DoubleClass avg)
if (list == list)
outp.print(" " + nameId + " ");
else
outp.print(" ");
outp.printf("%9d %15.2f%n", list, avg.getNum());
I guess I was trying to find a shortcut that ended up being a long cut. Here's the algorithm I wrote.
Algorithm
1.) Initialize the variables
2.) Get the student name and his/her accompanying 6 exam scores, limiting the number of scores to 6.
3a.) Calculate score of 6 exams for each student using void method called CalculateAverage.
3b.) Use a loop inside the method to read and sum the six scores.
4.) Use value-returning method CalculateGrade to determine and return each student's grade.
5.) Output each student's grade in void main.
6.) Calculate the average score for all students
7.) Output entire class average
And now I'm trying to piece together code to match each step of the algorithm starting from scratch.
So I got the code for outputting each students grade in void:
public static void printGrade(double testScore)
System.out.print("Line 10: Your grade for "
+ "the course is ");
if (testScore >= 90)
System.out.println("A");
else if (testScore >= 80)
System.out.println("B");
else if (testScore >= 70)
System.out.println("C");
else if (testScore >= 60)
System.out.println("D");
else
System.out.println("F");
This code can read the the file with the scores:
Scanner inFile =
new Scanner(new FileReader("a:\\studentlist.txt"));
PrintWriter outFile =
new PrintWriter("a:\\avg.out");
courseGrade = inFile.nextDouble();
studentName=inFile.nextChar();
while (inFile.hasNext())
studentName= inFile.next().charAt(0);
courseGrade= inFile.nextDouble();
I'm just trying to piece this thing together. Any tips would be appreciated. I will return with more pieces to the puzzle soon. As you can tell it's all kind of disorganized, and scatterbrained. Just trying to find some simplification or distillation, or recommendations.
WR

Answer 1

Hello,
Thanks for your reply. So I take it you are more familiar with Object Oriented Programming more than Procedural Based Programming?
Well the teacher insisted I follow the algorithm instead of trying to adapt another program to the problem. But sometimes that approach saves time I've noticed since many of the code examples we study in Java are like 'the golden oldies'.
The student gradebook problem is repeated over and over in different forms. Maybe if I just approached the problem more linearly:
Algorithm
1.) Initialize the variables
String studentId
int numberOfStudents
DoubleClass avg = new DoubleClass(); //average for a student
double avgGroup: //average for all students2.) Get the student name and his/her accompanying 6 exam scores.
Scanner group = new Scanner(new FileReader("c:\\list.txt"));
PrintWriter outfile = new PrintWriter("c:\\student.out"));
3a.) Calculate score of 6 exams for each student using void method called CalculateAverage using a loop to read and sum the six scores. The loop must be inside the method. It does not output the average score. The sum and average must be returned and output in void main.
method calculateAverage
double totalScore //to store the sum of all the scores of each student
int numberOfExams;  //to store the number of
int score; //to read and store a course score
double totalScore = 0.0
int numberOfExams = 0;
int score = 0;3b.) Use a loop inside the method to read and sum the six scores.
Using psuedocode (since the variables have been declared and initialized)
i)get the next student score
RIght here my approach of adapting another program to my new program becomes problematic
the pseudocode here is:
ii) while (score != -999):
I.) update totalScore by adding course score read in step i.
II.) increment numberOfExams by 1
III.) Get the nex student score
iii) studentAvg.setNum(totalScore / numberOfExams);
*What is the purpose of the statement while (score != -999)?*
I don't see why they picked -999?  Will this loop allow me to read an endless number of student names and theri accompanying number of exams and then find the average for each student?
I'll go into the next algorithmic steps later.
4.) Use value-returning method CalculateGrade to determine and return each student's grade.
5.) Output each student's grade in void main.
6.) Calculate the average score for all students
7.) Output entire class average
Thanks ahead of time for any suggestions, tips.