Sorting students by name and score using an array

Question

I posted a question about this last night but am still struggling. I need to sort a list of students from a text file first by name (in this format last name, first name), and then by test scores. I won't know how many students will be in the text file, other than that there is less than 100. I have to use the compareTo method (which I think I did correctly) and an array (I don't think I'm using this correctly). I have been messing around with this for literally hours on end and I just don't seem to get it. The text book really doesn't seem to be helping me any. How can I get my app class to print sorted student names/grades?

Other spefications are to get the average of the scores and make a comment next to any score below average. Those, however, I can work on after I can get the sorting straightened out.

Here is my code...

 package CH11AS8App;

 import java.io.FileReader;
 import java.util.Arrays;
 import java.util.Comparator;
 import java.util.Scanner;


 public class kjkkkkkkkkkkk {

 public static void main( String[] args ) throws Exception {
    // TODO Auto-generated method stub

        Scanner aScanner = new Scanner(
                                 new FileReader("src//chapt11//ch11AS8data.txt"));



        int numOfStudents = 100;
        Student[] studentArray = new Student[numOfStudents];
        Scanner sc = null;

        int counter = 0;
        while (aScanner.hasNext()) {
            sc = new Scanner(aScanner.nextLine());
            String lastName = sc.next();
            String firstName = sc.next();
            int score = sc.nextInt();


            studentArray[counter++] = new Student(lastName, firstName, score);

            studentArray[counter] = new Student(lastName, firstName, score); 

            int average= 0;
            int sum = 0;
            sum += score; 
             if (counter < numOfStudents); 
            average = sum / counter;
            if (score <= (average - 10)) {
             System.out.println("Score 10 points under average");
            System.out.println("Student Average:" + average);
        }



            sc.close();


            // Display Welcome Message
            System.out.println("Welcome to the Student Scores Application.\n");

            //Sort Names
            Arrays.sort(studentArray,0,counter, new Comparator<Student>(){
                @Override
                public int compare(Student s1, Student s2) {
                    return s1.getLastName().compareTo(s2.getLastName());
                }
            });

            System.out.println();
            System.out.println("Student list by name:");
            System.out.println();
            for(int j = 0; j < counter; j++){  
                System.out.println(studentArray[j]);

            }

            //Sort Scores
            Arrays.sort(studentArray,0,counter, new Comparator<Student>(){
                @Override
                public int compare(Student s1, Student s2) {
                    return Integer.valueOf(s2.getScore()).
                                       compareTo(Integer.valueOf(s1.getScore()));
                }
            });


            System.out.println();
            System.out.println();
            System.out.println("Student list by score:");
            System.out.println();
            for(int j = 0; j < counter; j++){  
                System.out.println(studentArray[j]);

            }


            //Close Scanner
            aScanner.close();

}

static class Student implements Comparable<Student> {

    //Instance Variables
    private String firstName;
    private String lastName;
    private int score;

    //Getters & Setters
    public Student( String firstName, String lastName, int score ) {
        this.firstName = firstName;
        this.score = score;
        this.lastName = lastName;
    }
    public int getScore() {
        return score;
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }


    //CompareTo Method
    @Override
    public int compareTo( Student s ) {

        if( !firstName.equalsIgnoreCase( s.firstName ) ) {

            return firstName.compareToIgnoreCase( s.firstName );
        }

        if( !lastName.equalsIgnoreCase( s.lastName ) ) {

            return lastName.compareToIgnoreCase( s.lastName );
        }
            return (new Integer(score)).compareTo((new Integer(s.score)));
    }
        @Override public String toString(){ return lastName + ", "+ firstName        +" : "+score; }


    }

 }

Solution 1

I think you should change your last line in compareTo as below:

    return (new Integer(examScore)).compareTo((new Integer(s.examScore));

or

    return Integer.valueOf(examScore).compareTo(Integer.valueOf(s.examScore));

This will compare the two values and return accordingly.

EDIT:

Some corrections in your program:

1. Add a toString() method in your Student class as:

   @Override public String toString(){ return firstName + " "+ lastName +" : "+examScore; }

2. Update the main() method in app as below:

   public static void main(String[] args) throws Exception {
   
       Scanner aScanner = new Scanner(
                              new FileReader("src//chapt11//ch11AS8data.txt"));
   
       System.out.println("Welcome to the Student Scores Application.\n");
   
       int nStudent = 100;
       Student[] studentArray = new Student[nStudent];
       Scanner lineScanner = null;
   
       int counter = 0;
       while (aScanner.hasNext()) {
           lineScanner = new Scanner(aScanner.nextLine());
           String lastName = lineScanner.next();
           String firstName = lineScanner.next();
           int examScore = lineScanner.nextInt();
           System.out.println("Student " + counter + " " + firstName + " "
                   + lastName + " " + +examScore);
   
           studentArray[counter++]=new Student(lastName, firstName, examScore);
           lineScanner.close();
       }
   
       for(int j = 0; j < counter; j++){  
           System.out.println(studentArray[j]);
       }
   
   
   
       //sort based on first name
       Arrays.sort(studentArray,0,counter, new Comparator<Student>(){
           @Override
           public int compare(Student s1, Student s2) {
               return s1.getFirstName().compareTo(s2.getFirstName());
           }
       });
       System.out.println("Students sorted by first name in ascending order");
       for(int j = 0; j < counter; j++){  
           System.out.println(studentArray[j]);
       }
   
       //sort based on score
       Arrays.sort(studentArray,0,counter, new Comparator<Student>(){
           @Override
           public int compare(Student s1, Student s2) {
               return Integer.valueOf(s1.getExamScore()).
                                  compareTo(Integer.valueOf(s2.getExamScore()));
           }
       });
       System.out.println("Students sorted by score in ascending order");
       for(int j = 0; j < counter; j++){  
           System.out.println(studentArray[j]);
       }
   
       //To compute the average:
       double sum = 0.0;
       for(int j = 0; j < counter; j++){  
           sum+=studentArray[j].getExamScore();
       }
       double average = (sum*1.0)/counter;
       System.out.println("Average Score = "+average );
   
   
       aScanner.close();
   }
   

Solution 2

Your mistake is in the last line of the compareTo() method:

change

return examScore = s.examScore;

to

return examScore - s.examScore;

You want to return a difference, not set your instance variable!