How to sort the average mark with elements in a text file in Java

Question

There is a text file which include student names, scores. I got the average marks of each student by using a Constructor. But, I have no idea how to sort the average marks with elements in the text file.

• John 95 75 88
• Alice 88 95 75
• Johnson 95 75 88
• Dennis 60 100 100
• Jack 77 84 93
• Tod 84 86 80
• Tom 68 70 75
• Dave 90 90 92
• David 99 70 87
• Trent 89 77 90
• Bob 100 67 89
• Fiona 77 89 90
• Peter 80 88 82
• Amy 85 95 78
• Nancy 83 93 82
• Richard 81 91 86
• Daniel 77 78 79
• James 80 90 85
• Cathy 95 74 89
• Paul 84 87 79

These are the element in the text file.

• Expected output like:
• Student Average Physic Chemistry Maths
• John 90 88 90 92
• Trent 88 87 88 89

    public class Student {
        String name;
        int physic;
        int chemistry;
        int math;
        int ave;

        public Student(String name, int physic, int chemistry, int math) {
            this.name = name;
            this.physic = physic;
            this.chemistry = chemistry;
            this.math = math;

            int sum = this.physic + this.chemistry + this.math;
            this.ave = sum / 3;
        }

        public void setName(String name) {
            this.name = name;
        }
        public void setPhysic(int physic) {
                this.physic = physic;
        }
        public void setChemistry(int chemistry) {
            this.chemistry = chemistry;
        }
        public void setMath(int math) {
            this.math = math;
        }

        public String getName() {
            return this.name;
        }
        public int getPhysic() {
            return this.physic;
        }
        public int getChemistry() {
            return this.chemistry;
        }
        public int getMath() {
            return this.math;
        }

        public int getAve() {
            return this.ave;
        }

    }

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

    class Main {
        public static void main(String[] args) {
                Student[] student = readData("students.txt");
            sortStudents(student);
            display();

        }
    private static Student[] readData(String filename) {
            int nStudent = 0;
            Student[] student = new Student[20];
            //filename = "students.txt";
            String string = null;

            try {
                FileReader fileReader = new FileReader(filename);
                BufferedReader bufferedReader = new BufferedReader(fileReader);

                while((string = bufferedReader.readLine()) != null) {
                        String[] arr = string.split(" ");
                        student[nStudent] = new Student(arr[0], Integer.parseInt(arr[1]), Integer.parseInt(arr[2]), Integer.parseInt(arr[3]));

                    nStudent++;
                }
                bufferedReader.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
            return student;
        }

        private static void display() {
            Student[] students = readData("students.txt");
            sortStudents(students);
            System.out.println("Student     AverageScore      Physic        Chemistry         Maths");
            for (int i = 0; i < students.length; i++) {
                System.out.println(students[i].getName() + "\t\t" + students[i].getAve() + "\t\t" + students[i].getPhysic() + "\t\t" + students[i].getChemistry() + "\t\t" + students[i].getMath());
            }
        }
    public static Student[] sortStudents(Student[] student) {
        //I need to sort the average marks of each student in the descending order.
        }
    }

Answer 1

You just need to change your smaller methods.

main():

public static void main(String[] args) {
    display();
}

display():

private static void display() {
    Student[] students = readData("students.txt");
    System.out.println("Student     AverageScore      Physic        Chemistry         Maths");
    for (Student student : students) {
        int[] sortedGrades = sortStudentGrades(student);
        System.out.println(student.getName() + "\t\t" + sortedGrades[0] + "\t\t" + sortedGrades[1] + "\t\t" + sortedGrades[2] + "\t\t" + sortedGrades[3]);
    }
}

The last thing that I changed was to change the sortStudents() method to the sortStudentGrades() method. Sorting students doesn't really do much good, and you there's no field to store the grades in the current Student object. As such, you need something that can sort an array of grades with the average without changing the Student object.

sortStudents() -> sortStudentGrades():

public static int[] sortStudentGrades(Student student) {
    int[] grades = new int[] {student.getAve(), student.getChemistry(), student.getPhysic(), student.getMath()};
    Arrays.sort(grades);
    return grades;
}

Hope that helps!

Answer 2

First take care about double cast. But you can implement the Comparable class like this

class Student implements Comparable<Student> {
private String name;
int physic;
int chemistry;
int math;
double ave;

public Student(String name, int physic, int chemistry, int math) {
    this.name = name;
    this.physic = physic;
    this.chemistry = chemistry;
    this.math = math;

    int sum = this.physic + this.chemistry + this.math;
    this.ave = (double)sum / 3;
}

@Override
public int compareTo(Student o) {
    return Double.compare(o.ave, ave);//for descending order
}    
}

and in your main you can use Arrays.sort(Student_tab); e.g:

import java.util.Arrays;

public static void main(String[] args) {
    Student a = new Student("john", 40, 23, 44);
    System.out.println("a = "+ a.ave);
    Student b = new Student("john", 50, 23, 44);
    System.out.println("b = "+ b.ave);

    Student[] tab = {a,b};
    Arrays.sort(tab);
    System.out.println(" 1: "+ tab[0].ave);
    System.out.println(" 2: "+ tab[1].ave);
}

Indeed the array of students is ordered we get the following result:

//Disorder:

a = 35.666666666666664
b = 39.0

//Ordered:

1: 39.0
2: 35.666666666666664