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; }
}
}
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:
Add a toString() method in your Student class as:
@Override public String toString(){ return firstName + " "+ lastName +" : "+examScore; }
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();
}