Inheritance error?

[Kevin Tansey]

I'm trying to call a method to get a value...

but I'm not sure exactly how to do it!

This is a small part of a large project, I'm just plugging away at trying to do each portion one at a time.

I have several files, and here's how they stand right now, I will describe where my problem is right now at the end:

Student.java

import java.io.*;
import java.util.*;
import javax.swing.*;
import java.text.*;
 
public class Student {
    private Name fullName;
    private String id; // identification number
    private Transcript transcript;
    
        private static final String END_OF_FILE_STR = "END"; // indicates end of file
        private static final int DEFAULT_SIZE = 3;   
        private static Course semesterList[] = new Course[DEFAULT_SIZE]; // course list
        private static int  courseCount; // number of student courses loaded from a file
    
    public Student() 
    {
        fullName = new Name();
        id = "";
        transcript = new Transcript();
    } // end default constructor
 
    
    public Student(Name studentName, String studentId) 
    {
        fullName = studentName;
        id = studentId;
        transcript = new Transcript();
    } // end constructor
 
    public void setStudent(Name studentName, String studentId) 
    {
        setName(studentName); // or fullName = studentName;
        setId(studentId); // or id = studentId;
    } // end setStudent
 
    public void setName(Name studentName) 
    {
        fullName = studentName;
    } // end setName
 
    public Name getName()
    {
        return fullName;
    } // end getName
 
    public void setId(String studentId)
    {
        id = studentId;
    } // end setId
 
    public String getId()
    {
        return id;
    } // end getId
 
    public String toString()
    {
        return id + " " + fullName.toString();
    } // end toString
 
    public void setTranscript(int num, Course[] c) 
    {
        transcript.setNumCourses(num);
        for (int i = 0; i < num; i++) 
        {
            transcript.setCourseTitle(i, c[i].getTitle());
            transcript.setCourseNumCredits(i, c[i].getNumCredits());
            transcript.setCourseGrade(i, c[i].getGrade());
        }
    }
 
    public Transcript getTranscript() 
    {
        return transcript;
    }
 
    /*------------------------------------------------------------*/
    /*                   Helper methods                           */
    
    /**
     * Creates a new course by processing
     * the data provided in the file
     *
     * @param line   a single line of input.
     *
     * @return a course object created from the input line;
     *         a null is returned if there's an error in input line
     */
    private Course createCourse(String line) {
        Course  course = null;
        String  title;
        int     numCredits;
        String  grade;
        Scanner scanner = new Scanner(line);
 
        try {
           
//ADD CODE HERE
//USING SCANNER GET title, numCredits,
//AND grade DATA FROM THE INPUT LINE
            
//CREATE A course OBJECT WITH THIS DATA
  
 
        } catch (InputMismatchException e) {
            course = null;
        }
        return course;
    }
 
    
    /**
     * Builds the list of courses array.
     *
     * @param filename the name of the file to load
     *                 the student info
     *
     * @return true if the operation is successful;
                    false otherwise.
     *
     */
    private boolean buildSemesterList(String filename) {
        String  inputLine;
        Course  course;
 
        File             inFile;
        Scanner          scanner;
 
        boolean status   = true;
        boolean done     = false;
 
        try {
           inFile = new File(filename);
 
           scanner = new Scanner(inFile);
 
           while ( !done ) {
           
//         ADD CODE HERE
 
//         USING SCANNER, READ DATA FROM THE FILE ONE LINE AT THE TIME
//         CREATE course OBJECT BY CALLING createCourse METHOD                   
//         IF THE LINE IS END_OF_FILE_STR THEN STOP 
 
//         ADD THE course TO THE semesterList ARRAY. BUT BEFORE YOU DO THAT
//         CHECK IF THE semesterList ARRAY IS FULL
//         IF IT IS, DOUBLE ITS SIZE AND UNCOMMENT THE FOLLOWING LINE:
//         System.out.println("Increased the semesterList array to size of " + semesterList.length);
                           
//         AFTER ADDING A course TO THE semesterList ARRAY
//         DO NOT FORGET TO INCREMENT THE courseCount VARIABLE
 
 
               inputLine = scanner.nextLine();
               if(inputLine.equalsIgnoreCase(END_OF_FILE_STR))
               {
               done = true;
               }
               else if(courseCount == semesterList.length){
               int newLength = (int) (2 * semesterList.length);
               Course[] temp = new Course[newLength];
               
               for (int i=0; i < semesterList.length; i++){
               temp[i] = semesterList[i];
               }
               semesterList = temp;
               System.out.println("Increased the semesterList array to size of " + semesterList.length);
               }
               
               else{
               course = createCourse(inputLine);
               if (course !=null)
               {
               semesterList[courseCount] = course;
               courseCount++;
               }
               }
               
 
           } // while
 
           scanner.close();
        }
        catch (IOException e) {
            status = false;
        }
 
        return status;
    }
    /**
     * Open a textfile, read in data, and
     * construct the list of courses array.
     *
     * @return true if the operation is successful
     *
     */
    private boolean readData() {
       
// MODIFY THE FOLLOWING CODE TO START 
// THE LISTING FROM THE CURRENT DIRECTORY
        JFileChooser fileChooser = new JFileChooser(".");
 
        int returnVal = fileChooser.showOpenDialog(null);
 
        boolean result = false;
 
        if(returnVal == JFileChooser.APPROVE_OPTION) {
           String filename = fileChooser.getSelectedFile().getAbsolutePath();
 
            if (filename != null) {
 
                result = buildSemesterList(filename);
            }
        }
 
        return result;
    }
    /**
     * Loads the data from a file, computes the GPA,
     * and displays the transcript.
     *
     */
    public void processData() {
 
         if (!readData()) {
            System.out.println("File Input Error");
         }
    }  
    public static void main(String[] args) 
    {
        Student student1 = new Student();
        student1.processData();
        DecimalFormat df = new DecimalFormat("0.00");
 
        student1.setTranscript(courseCount,semesterList);
        
        Transcript tran = student1.getTranscript();
        System.out.println("The whole transcript for student1");
        System.out.println(tran);
        // CORRECT THE printf STATEMENT SO IT PRINTS ONLY
// TWO DIGITS AFTER THE DECIMAL POINT
        System.out.printf("The gpa is %9f\n", 
                             df.format(student1.getTranscript().getGPA()));
        System.out.println();
      
        System.out.println("Java for student1 -- " 
            + student1.getTranscript().getCourse("Java"));
        int index = student1.getTranscript().getWorstGradeIndex();
        System.out.println("Worst grade for student1 -- " 
            + student1.getTranscript().getCourse(index));       
        if (index >= 0){  
           System.out.println("Change the grade to A");
           tran.setCourseGrade(index,'A');
           System.out.println("The course for student1 is now -- " +
                student1.getTranscript().getCourse(index));
// CORRECT THE printf STATEMENT SO IT PRINTS ONLY
// TWO DIGITS AFTER THE DECIMAL POINT       
        System.out.printf("The gpa is now %9f\n", 
                              df.format(student1.getTranscript().getGPA()));
        }
    }
}

Course.java

public class Course {
private String title;
private int numCredits;
private Grade grade;
 
public Course() 
{
title = new String("");
numCredits = 0;
grade = new Grade();
}
 
public Course(String t, int credits) 
{
title = new String(t);
numCredits = credits;
grade = new Grade();
}
 
public void setTitle(String t) 
{
title = t;
}
 
public String getTitle() 
{
return title;
}
 
public void setNumCredits(int credits) 
{
numCredits = credits;
}
 
public int getNumCredits() 
{
return numCredits;
}

public int getQualityPoints() 
{
return grade.qualityPoints();
}
 
public void setGrade(char g) 
{
grade.setLetterGrade(g);
}
 
public char getGrade() 
{
return grade.getLetterGrade();
}

public String toString()
{
return null;
// ADD CODE HERE
// IMPLEMENT THE METHOD 
 
}
 
}

Grade.java (I'm done with this one, yay

public class Grade  
{
    private char letterGrade;
 
    public Grade() 
    {
        letterGrade = ' ';
    }
 
    public Grade(char g) 
    {
        letterGrade = g;
        Character.toUpperCase(letterGrade);
    }
 
    public int qualityPoints() 
    {
        int qp = 0;
        
        switch(letterGrade){
        
//      ADD CODE HERE
//      CALCULATE THE qp USING THE FOLLOWING MAPPING:
//      'A' is 4
//      'B' is 3
//      'C' is 2
//      'D' is 1
//      'F' is 0
        
            case 'A': qp = 4;
                break;
            case 'B': qp = 3;
                break;
            case 'C': qp = 2;
                break;
            case 'D': qp = 1;
                break;
            case 'F': qp = 0;
                break;
            default: System.out.print("Input error: Invalid grade data");
                break;
        }
 
        return qp;
    }
 
    public void setLetterGrade(char g) 
    {
        letterGrade = g;
        Character.toUpperCase(letterGrade);
    }
 
    public char getLetterGrade() 
    {
        return letterGrade;
    }
}

Name.java (dont think I need to touch this one at all)

public class Name
{
private String first;  // first name
private String last;   // last name
 
public Name()
{
} // end default constructor
 
public Name(String firstName, String lastName)
{
first = firstName;
last = lastName;
} // end constructor
 
public void setName(String firstName, String lastName)
{
setFirst(firstName);
setLast(lastName);
} // end setName
 
public String getName()
{
return toString();
} // end getName
 
public void setFirst(String firstName)
{
first = firstName; 
} // end setFirst
 
public String getFirst()
{
return first;
} // end getFirst
 
public void setLast(String lastName)
{
last = lastName;
} // end setLast
 
public String getLast()
{
return last;
} // end getLast
 
public void giveLastNameTo(Name aName)
{
aName.setLast(last);
} // end giveLastNameTo
 
public String toString()
{
return first + " " + last;
} // end toString
} // end Name

Transcript.java (this is the fun one...)

public class Transcript  {
private int numCourses;
Course courses[];
 
public Transcript() 
{
numCourses = 0;
}
 
public Transcript(int num) 
{
numCourses = num;
courses = new Course[numCourses];
for (int i=0; i<num; i++)
courses[i] = new Course();
}
 
public void setNumCourses(int num) 
{
numCourses = num;
courses = new Course[numCourses];
for (int i=0; i<num; i++)
courses[i] = new Course();
}
 
public int getNumCourses() 
{
return numCourses;
}
 
public void setCourseTitle(int num, String title) 
{
courses[num].setTitle(title);
}
 
public String getCourseTitle(int num) 
{
return courses[num].getTitle();
}
 
public void setCourseNumCredits(int num, int credits) 
{
courses[num].setNumCredits(credits);
}
public int getCourseNumCredits(int num) 
{
return courses[num].getNumCredits();
}
 
public void setCourseGrade(int num, char g) 
{
courses[num].setGrade(g);
// ADD CODE HERE
// FINISH THE METHOD
}
 
public char getCourseGrade(int num) 
{
return courses[num].getGrade();
}


 
public Course getCourse(int num)
{
if(inRange(num))
return courses[num];
else
return null;
}
 
public Course getCourse(String title) 
{
Course result = null;

int count = courses.length;
int index = 0;
boolean found = false;
 
while(index < count  && !found)
{
if(title.equals(courses[index].getTitle()))
{
result = courses[index];
found = true;
}
index++;
// ADD CODE HERE
// SEQUENTIALLY SEARCH ARRAY courses FOR THE COURSE
// OF THE GIVEN TITLE. IF FOUND, SET THE result TO 
// THE FOUND COURSE
}
return result;
}
public boolean inRange(int num)
{
return (num >=0 && num<courses.length);
}
 
public double getGPA()
{
double sum = 0.0; 
double credits = 0.0; 
 
for(int i = 0; i<courses.length; i++)
{
credits = getCourseNumCredits(i);

sum+= (Course.getQualityPoints() * credits);

// ADD CODE HERE
// CALCUTE sum BY ADDING (COURSE QUALITY POINTS * COURSE NUMBER OF CREDITS)
// FOR EACH COURSE
 
// CALCULATE credits THAT IS A SUM OF CREDITS FOR EACH COURSE
 
}
     //return GPA
return sum/credits;
}

public int getWorstGradeIndex()
{
int worst = -1;
if (courses != null)
{
while (worst < courses.length)
{
if(getCourseGrade(worst) < worst)
{
worst = getCourseGrade(worst);
}
worst++;
}
}

// ADD CODE HERE
// IF THE ARRAY courses IS NOT EMPTY 
// FIND AN INDEX OF THE COURSE WITH
// THE LOWEST GRADE
 
return worst;
}

public String toString()
{
String result;

result = "\nTranscript:\n";
for(int i=0; i<courses.length; i++)
result = result + "\t" + courses[i].toString() +"\n";
return result;
}
 
public static void main(String[] args) 
{
Transcript transcript1 = new Transcript();
}
 
}

The problem I'm working on right now is the getGPA() method of Transcript.java - where I am supposed to get the sum by multiplying the course quality points by the number of credits.

I have:

public double getGPA()
{
double sum = 0.0; 
double credits = 0.0; 
 
for(int i = 0; i<courses.length; i++)
{
credits = getCourseNumCredits(i);

sum+= (Course.getQualityPoints() * credits);

// ADD CODE HERE
// CALCUTE sum BY ADDING (COURSE QUALITY POINTS * COURSE NUMBER OF CREDITS)
// FOR EACH COURSE
 
// CALCULATE credits THAT IS A SUM OF CREDITS FOR EACH COURSE
 
}
     //return GPA
return sum/credits;
}

And the error I am getting on this is:
"Cannot make a static reference to the non-static method getQualityPoints() from the type Course"

Does this mean I need to make a call to Course.getQualityPoints() and assign that to a new variable?
[ December 11, 2005: Message edited by: Kevin Tansey ]

[Kevin Tansey]

I just tried that and it gives the same error about static reference...

public double getGPA()
{
double sum = 0.0; 
double credits = 0.0; 
int QP = 0;

for(int i = 0; i<courses.length; i++)
{
credits = getCourseNumCredits(i);
QP = Course.getQualityPoints();

sum+= (QP * credits);

// ADD CODE HERE
// CALCUTE sum BY ADDING (COURSE QUALITY POINTS * COURSE NUMBER OF CREDITS)
// FOR EACH COURSE
 
// CALCULATE credits THAT IS A SUM OF CREDITS FOR EACH COURSE
 
}
     //return GPA
return sum/credits;
}

[Kevin Tansey]

alright, I think I got it...

public double getGPA()
{
double sum = 0.0; 
double credits = 0.0; 
int QP = 0;

for(int i = 0; i<courses.length; i++)
{
credits = getCourseNumCredits(i);
QP = courses[i].getQualityPoints();

sum+= (QP * credits);

// ADD CODE HERE
// CALCUTE sum BY ADDING (COURSE QUALITY POINTS * COURSE NUMBER OF CREDITS)
// FOR EACH COURSE
 
// CALCULATE credits THAT IS A SUM OF CREDITS FOR EACH COURSE
 
}
     //return GPA
return sum/credits;
}

feel free to delete this post unless you'd like to give me pointers on any of the other stages I need to complete