I'm having trouble properly filling an array, I think

Question

I'm having a bit of trouble formatting my code to give the correct output. I'm a beginner at Java, so I expect I've made some rather stupid mistakes, but here goes.

The text file that I'm inputting is:

John Smith  90
Barack Obama    95
Al Clark    80
Sue Taylor  55
Ann Miller  75
George Bush 58
John Miller 65

---

The output file looks a little something like this:

John Smith  90
Barack Obama    95
Al Clark    80
Sue Taylor  55
Ann Miller  75
George Bush 58
John Miller 65

Students with excellent grades:
John Smith  90
Barack Obama    95

Students with ok grades:
Al Clark    80
Ann Miller  75
John Miller 65

Students with failure grades:
Sue Taylor    55
George Bush  58


Lowest Grade: Sue Taylor 55 
Highest Grade: Barack Obama 95
Average of Grades: 74


Grades in descending order: 
John Smith 55 
Barack Obama    58 
Al Clark    65 
Sue Taylor  75 
Ann Miller  80 
George Bush 90 
John Miller 95 

---

The output that I'm looking for is this:

The output file looks a little something like this:

John Smith  90
Barack Obama 95
Al Clark 80
Sue Taylor   55
Ann Miller   75
George Bush  58
John Miller  65


Students with excellent grades:
John Smith  90
Barack Obama 95


Students with ok grades:
Al Clark   80
Ann Miller   75
John Miller  65


Students with failure grades:
Sue Taylor    55
George Bush  58


Lowest Grade: Sue Taylor 55
Highest Grade: Barack Obama 95
Average of Grades: 74


Grades in descending order: 
Barack Obama 95
John Smith 90
Al Clark 80
Ann Miller 75
John Miller 65
George Bush 58
Sue Taylor 55

---

The issues are:

1. I need to have the names (first and last) print the grades for the minimum and maximum. 牌号为最小和最大打印。

2. The descending order of the grades is obviously ascending, so that needs to be fixed.

3. I also need the names (first and last) to print with each grade in the organized descending list at the end, right now the names don't match up to the grades.

---

Here's my code:

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

public class Students
{
public static void main (String[] args) throws IOException
{   
    String first_name, last_name;
    int grade, total=0, count=0;
    int min, max;

    double average;

     int excellentTotal = 0;
     int okTotal = 0;
     int failureTotal = 0;

    Scanner fileInput = new Scanner(new File("students.txt"));
    Student st[] = new Student [100];
    while (fileInput.hasNext())
    {
        first_name = fileInput.next();
        last_name = fileInput.next();
        grade = fileInput.nextInt();    
        st[count] = new Student(first_name, last_name, grade);
        count++;
        total = total + grade; 
    }

    for (int i=0; i<count;i++)
    {
        System.out.println(st[i]);
    }

    System.out.println("\nStudents with excellent grades:");
    for (int i=0; i<count;i++)
    {
        if (st[i].grade > 89)
        {
            System.out.println(st[i]);
            excellentTotal += st[i].grade;
        }
    }

    System.out.println("\nStudents with ok grades:");
    for (int i=0; i<count;i++)
    {
        if (st[i].grade >=60 && st[i].grade <=89)
        {
            System.out.println(st[i]);
            okTotal += st[i].grade;
        }
    }

    System.out.println("\nStudents with failure grades:");
    for (int i=0; i<count;i++)
    {
        if (st[i].grade < 60)
        {
            System.out.println(st[i]);
            failureTotal += st[i].grade;
        }
    }       


    min = st[0].getGrade();
    max = st[0].getGrade();
    for (int i = 0; i < count; i++) 
    {
        if (max.grade < st[i].grade)
        {
            max = st[i];
        }
        if (min.st[i] > st[i].grade)
        {
            min = st[i].grade;
        }
        total = excellentTotal + okTotal + failureTotal;
    }

    System.out.println();
    System.out.println("Lowest Grade: " + min);
    System.out.println("Highest Grade: " + max);
    System.out.println("Average of Grades: " + total/count);

    int t, swap = 0;
    do 
    { 
        swap = 0; 
        for (int i=0; i<count-1; i++) 
        {
            if (st[i].getGrade()>st[i+1].getGrade()) 
            {
                t=st[i].grade; 
                st[i].grade=st[i+1].grade; 
                st[i+1].grade=t; 
                swap++;
            }
        } 
    }
    while (swap>0);

    System.out.println("\nGrades in descending order: ");

    for (int i=0; i<count;i++)
    {
         System.out.print (st[i] + " ");
         System.out.println ();
    }
}
static class Student
{
    private String fname, lname;
    private int grade;

    public Student(String fname, String lname, int grade)
    {
        this.fname = fname;
        this.lname = lname;
        this.grade = grade;
    }

    public int getGrade() 
    {
        return grade;
    }

    public void setGrade(int grade) 
    {
        this.grade = grade;
    }


    public String toString()
    {
        return fname + " " + lname + "\t" + grade;
    }


}
}

Answer 1

The issues are:

1. I need to have the names (first and last) print with the grades for the minimum and maximum.

Keep two Strings that each contain the name of the person with the min and max grade, just like you did with the actual min and max value.

1. The descending order of the grades is obviously ascending, so that needs to be fixed.

It looks like you've already sorted your array so that it is in ascending order (Btw look in to Arrays.sort() if you're allowed), so instead of printing it from front to back, why don't you print it starting from the end of your array? This should print it in descending order.

1. I also need the names (first and last) to print with each grade in the organized descending list at the end.

Your grades aren't matching up with the correct person because you're switching the grades of each person in the array, instead of switching the People around in the array.

See here:

t=st[i].grade; 
st[i].grade=st[i+1].grade; 
st[i+1].grade=t;

Let's pretend you have 2 people, Bob and Sam, with grades of 50 and 75,respectively.

Here they are in the array: [Bob(50)][Sam(75)]

Using the above code to swap them, you would end up with this: [Bob(75)][Sam(50)]

The changes to fix this are trivial. I'll leave it to you to figure out.

Answer 2

okay, a quick and dirty example of what I would do:

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Students {

List<Student> students = new ArrayList<Student>();

public Students() {
    // create quick list, no reading from file, don't use arrays if you can help it
    students.add(new Student("a", 1));
    students.add(new Student("b", 2));
    students.add(new Student("c", 3));

    // sort list descending
    Collections.sort(students, new Comparator<Student>() {
        @Override
        public int compare(Student student1, Student student2) {
            return -1 * student1.grade.compareTo(student2.grade);
        }
    });
}

public void showDescending() {
    // just so the list that was sorted descending
    System.out.println(students);
}

public void showForRange(Integer minGrade, Integer maxGrade) {
    // show all students with grades between minGrade and maxGrade
    for (Student s : students) {
        if (s.grade >= minGrade && s.grade <= maxGrade) {
            System.out.println(s);
        }
    }
}

public class Student {
    String name;
    Integer grade;

    public Student(String name, Integer grade) {
        this.name = name;
        this.grade = grade;
    }

    // use toString to easily show name with grade for each student in list
    @Override
    public String toString() {
        return name + " " + grade;
    }

}

public static void main(String[] args) {
    Students s = new Students();
    s.showForRange(100, 90);
    s.showForRange(89, 80);
    s.showDescending();

}


}