Java Newbie in need of assistance, reading lines from text file and calculating averages.

[Aaron Best]

Hello, JavaRanch. My name's Aaron, and as this thread's title states, a newbie to the Java world. I understand a little about Java after 9 weeks of classes/labs, even more since I have a few friends who can help. I'm here today to ask for assistance regarding a code I'm working on now. The situation is, I need to read data from an external text file (which I've already completed), break the contents into tokens with StringTokenizer (also completed), then output the data in the format:

Students with grades of X between Y:
LastName FirstName Grade
LastName FirstName Grade
... and so on

I need to do this for the following ranges; 69 and below, 70 to 79, 80 to 89, and 90 to 100 (I've also done this). But the problem is, the output is all screwed up. Here's the code:

import java.io.*;
import java.util.*;

class NewGrades
{
   public static void main(String[] args) throws IOException
   {
   
   String firstName = null, lastName = null, filename;
   String gradeChecker = null, strLine;
   int grade = 0, linesWithGrades = 0;
   double avg = 0;
   
   filename = "GPA.txt";
   StringTokenizer st;
   BufferedReader br;
   br = new BufferedReader(new FileReader(filename));
   
   while ((strLine = br.readLine()) != null) {
      st = new StringTokenizer(strLine, " ");
      try {
         while (st.hasMoreTokens()) {
            firstName = st.nextToken();
            lastName = st.nextToken();
            gradeChecker = st.nextToken();
            if (firstName == null || lastName == null || gradeChecker == null) {
            
            } else {
               grade = Integer.parseInt(gradeChecker);
               if (grade < 69) {
                  avg += grade;
                  linesWithGrades++;
                  System.out.println("Students with grades 69 and below: ");
                  System.out.println(lastName + " " + firstName + "\t" + grade);
               } else if (grade > 69 && grade < 80) {
                  avg += grade;
                  linesWithGrades++;
                  System.out.println("Students with grades between 70 and 79: ");
                  System.out.println(lastName + " " + firstName + "\t" + grade);
               } else if (grade > 79 && grade < 90) {
                  avg += grade;
                  linesWithGrades++;
                  System.out.println("Students with grades between 80 and 89: ");
                  System.out.println(lastName + " " + firstName + "\t" + grade);
               } else if (grade > 89 && grade < 101) {
                  avg += grade;
                  linesWithGrades++;
                  System.out.println("Students with grades of 90 and above: ");
                  System.out.println(lastName + " " + firstName + "\t" + grade);
               } else if (gradeChecker == null) {
						System.out.println("Persons with no grade or incomplete data: ");
						System.out.println(lastName + firstName);
               }
            }
         }
		} catch (Exception e) {
            System.out.println("Exception while reading GPA file: " + e);
         }
   }
         System.out.println();
         System.out.println();
         System.out.print("The grade point average is" + "\t" + Math.ceil(avg / linesWithGrades));
         System.out.println();
   }
}

The output turns out like this:

 ----jGRASP exec: java NewGrades

Students with grades between 80 and 89: 
Clinton Bill	85
Students with grades of 90 and above: 
Gore Al	100
Students with grades of 90 and above: 
Bush George	95
Students with grades between 80 and 89: 
Clinton Hillery	83
Students with grades between 70 and 79: 
McCain John	72
Students with grades between 80 and 89: 
Green Danna	87
Students with grades between 70 and 79: 
Delaney Steve	76
Exception while reading GPA file: java.util.NoSuchElementException
Students with grades 69 and below: 
Bills Beth	60
Students with grades of 90 and above: 
Takei Rhea	94
Students with grades between 70 and 79: 
Uetake Ami	77
Students with grades of 90 and above: 
Ieyasu Aoi	100
Students with grades of 90 and above: 
Nishihara Eri	100
Students with grades of 90 and above: 
Fanelitz Amelia	100
Students with grades between 80 and 89: 
Rheyin Krystal	87
Exception while reading GPA file: java.util.NoSuchElementException
Exception while reading GPA file: java.util.NoSuchElementException


The grade point average is	87.0

 ----jGRASP: operation complete.

See what I mean? What I'm trying to do is get it so each person is under the correct range without the range showing up so many times. I also need to output the names of people who don't have any grades available, but those turn out as Exceptions. Can anyone give me a hand here? Thanks in advance.

[Callum Ludwig]

Hi Aaron,

The problem with your output is you are printing the title Students with grades between X and Y for each row you read in from the file.

Now I’m not the smartest algorithmic programmer but I would do something like this.

Make an inner class called student

class Student {
	private String name; //combination of first and last name or you could split this up if you want into 2 separate private String variables.
	private int grade;

	//getters and setter methods for above variables
}

Then as you read in each line create a Student object, using your current if statement (which could be supplemented with a switch statement), place the new Student object into a Map, that holds a list of students under a specific key. So the key in the map for each Student object list will be your title “Students with grades between X and Y”, get the list belonging with that key and place the student into the list. So you would have 4 entries in the map, corresponding to a List holding the students that fall into that particular grade category.

Once you’ve read in all the students and placed them into their corresponding list assigned to the key. Iterate through the map keys and for each key iterate through the list of students. At the same time totaling up ALL the grades to get the grade average.

Which then should give you your desired output. Sorry about the brief explanation but I’m at work and can’t do a detailed example, but hopefully you get what I’m trying to say.

As for Exception handling, I don't have much time to go into ideas for that. Sorry.

Hope it helps you with your work.

[Campbell Ritchie]

Welcome to the Ranch

Please always use an informative thread title; since you are new I have added something to the title, and I hope I got it right.

CL: I hope the use of Maps and Lists isn't beyond him.

[Ralph Cook]

First thing to realize: you are going to have to read all your students into some kind of collection before you start your output. You cannot read one student at a time and output their info if you want to collect students by grade range.

You can declare an "inner class" as specified, or put that in its own file named Student.java. You are going to need some way to store a name (or two) and a grade for each student.

The other poster is correct; store the name (in one or two variables) and the grade in the Student class. You can plan to create a student object with a constructor that takes these items, and a pair of methods to get the values out of the object. This is a complete Student class; the fact that mine is declared "public" class means it has to be in its own file. If you declare it as the other poster suggested, you can declare it in this file.

public class Student
{ private String name;
   private int      grade;

  public Student(String givenName, int givenGrade)
  {
    name = givenName; 
    grade = givenGrade;
  }

  public int getGrade() { return grade; }
  public String getName() { return name; }
}

and then in your code:

  // this declaration can be an instance variable in your NewGrades class
  ListArray students = new ListArray();

  // then, within the reading loop
  // code here to get a full name and a grade, as you already do
  Student currentStudent = new Student(fullName, grade)
  students.add(currentStudent);

  // with that you have created a Student object and added it to the list.  It does not
  // matter that you reassign a new student to currentStudent each time through the list, because
  // you are going to access them through the list, not through that variable.

  // so once you are done building your list, you can go through it once per grade range
  System.out.println("Students with grades 69 and below: ");
  for (student: Student in students)
  { if (student.getGrade() <= 69)
      { System.out.println(student.getName() + "\t" + student.getGrade());
      }

  // etc.
}

Now, there are multiple things about this code that can be improved and teach you more about writing good code -- it's a good exercise -- but rather than try to do all of those at once, I think this may be enough information for you to go ahead and finish this task the way you wanted to.

Let us know.

rc

[Aaron Best]

Yeah, sorry about that everyone. I had a few problems that had to be dealt with. As far as the code goes, I've revised it. As far as Maps and Lists go, I'm afraid that's beyond my level of skill.. I had a little help from a friend, who told me to make strings for each range and my code came out like this:

import java.io.*;
import java.util.*;

class NewGrades
{
   public static void main(String[] args) throws IOException
   {
   
	String firstName = null, lastName = null, gradeString = null, filename;
   String strLine;
	// Initializing new Strings for each range
	String firstRange = "", secondRange = "", thirdRange = "", fourthRange = "", noData = "";
   int grade = 0, linesWithGrades = 0;
   double avg = 0;
   
   filename = "GPA.txt";
   StringTokenizer st;
   BufferedReader br;
	try {
   	br = new BufferedReader(new FileReader(filename)); // Required to read the file
   
   	while ((strLine = br.readLine()) != null) {
      	st = new StringTokenizer(strLine, " ");
      	try {
         	while (st.hasMoreTokens()) {
            	firstName = st.nextToken();
            	lastName = st.nextToken();
					gradeString = st.nextToken();
					grade = Integer.parseInt(gradeString);
               if (grade > 0 && grade < 69) {
                  avg += grade;
                  linesWithGrades++;
						firstRange += lastName + " " + firstName + "\t" + grade + "\n";
               } else if (grade > 69 && grade < 80) {
                  avg += grade;
                  linesWithGrades++;
						secondRange += lastName + " " + firstName + "\t" + grade + "\n";
               } else if (grade > 79 && grade < 90) {
                  avg += grade;
                  linesWithGrades++;
						thirdRange += lastName + " " + firstName + "\t" + grade + "\n";
               } else if (grade > 89 && grade < 101) {
                  avg += grade;
                  linesWithGrades++;
						fourthRange += lastName + " " + firstName + "\t" + grade + "\n";
               }
					// To avoid adding the wrong data to noData, the variables are cleaned
					firstName = "";
					lastName = "";
					gradeString = "";
         }
		} catch (Exception e) {
            // Catches null data for noData
				noData += lastName + " " + firstName + "\t" + gradeString + "\n";
         }
   }
				} catch (Exception e) {
				System.out.println("Exception while reading GPA file: " + e);
			}
			System.out.println("Students with grades 69 and below: ");
			System.out.println(firstRange);
			System.out.println("Students with grades between 70 and 79: ");
			System.out.println(secondRange);
			System.out.println("Students with grades between 80 and 89: ");
			System.out.println(thirdRange);
			System.out.println("Students with grades of 90 and above: ");
			System.out.println(fourthRange);
			System.out.println("Persons with no grade or incomplete data: ");
			System.out.println(noData);
            System.out.println();
            System.out.println();
            System.out.print("The grade point average is" + "\t" + Math.ceil(avg / linesWithGrades));
            System.out.println();
   }
}
                  

Now, there's one last problem. A new addition to this assignment is, if I understood it right, to output the data I get from running the program to a new file, like "GPA2.txt". I believe my professor wants me to use PrintWriter, but I'm not entire sure I understand how it works. I know the constructor for it:

public PrintWriter(Writer out, boolean autoFlush)

But I don't understand how the parameters work here. Once I figure this out, get in my code, and print my output to a new file, I'll be officially done. So I must again ask for your assistance here, everyone. ^_^;