Collections sorting a list made of generic class objects

Hi, I need to write a program that uses the Collections sort method in order to sort through an ArrayList with objects from a generic class.

My generic class looks like:

Code:

---

public class Pair<F, S> {
        public F firstObject;
        public S secondObject;
       
       
        public Pair(F a, S b) {
        firstObject = a;
        secondObject = b;               
        }
}

---

I also have the Comparator classes ready.

The problem is in the main method where I'm reading the values from a text file and it looks something like:

Code:

---

ArrayList<Pair> list = new ArrayList<Pair>();
while(sc.hasNextLine())
                        list.add(new Pair(new Advisor(sc.next()), new Student(sc.next(), sc.nextDouble())));
               
                for(Pair e: list)
                        System.out.println(e);       
       

                Collections.sort(list, new AdvisorPairComparator());
               
                System.out.println("*** Sorted by advisor name  ***");
                for(Pair e: list)
                        System.out.println(e);

---

So I keep getting an error saying: "The method sort(List<T>, Comparator<? super T>) in the type Collections is not applicable for the arguments (ArrayList<Pair>, AdvisorPairComparator)"

Any ideas?

Thanks!

How is AdvisorPairComparator defined?

Code:

---

import java.util.Comparator;


public class AdvisorPairComparator implements Comparator<Advisor>{       
       
        @Override
        public int compare(Advisor a1, Advisor a2) {
                if(a1.getName().equals(a2.getName()))               
                return 0;
                else{
                        int ceil = a1.getName().length()>a2.getName().length()?a2.getName().length():a1.getName().length();
                       
                        for(int i=0; i < ceil; i++) {
                                char c1 = a1.getName().charAt(i);
                                char c2 = a2.getName().charAt(i);
                               
                                if(c1 != c2)
                                        return (c1<c2)?-1:1;
                        }
                       
                        return a1.getName().length()>a2.getName().length()?1:-1;                       
                }
        }
       
}

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There are many undefined classes so the code won't compile.

If the list contains Pair objects, how can the Comparator for Advisor work with it?

Ok, so I made some changes to the code and my main class looks like this:

Code:

---

import java.io.File;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;


public class Driver {

       
        @SuppressWarnings("unchecked")
        public static void main(String[] args) throws Exception{
               
                ArrayList<Pair> list = new ArrayList<Pair>();
                Scanner sc = new Scanner(new File("data.txt"));
               
                while(sc.hasNextLine())
                        list.add(new Pair<Advisor, Student>(new Advisor(sc.next()), new Student(sc.next(), sc.nextDouble())));
               
                for(Pair<Advisor, Student> e: list)
                        System.out.println(e);       
       

        Collections.sort(list, new AdvisorPairComparator());
               
                System.out.println("*** Sorted by advisor name  ***");
                for(Pair e: list)
                        System.out.println(e);       
               
                Collections.sort(list, new StudentNamePairComparator());
               
                System.out.println("*** Sorted by student name  ***");
                for(Pair e: list)
                        System.out.println(e);
               
                Collections.sort(list, new StudentGpaPairComparator());
               
                System.out.println("*** Sorted by student GPA  ***");
                for(Pair<Advisor,Student> e: list)
                        System.out.println(e);       
       
        }
}

---

and my comparator class looks like this:

Code:

---

import java.util.Comparator;

public class AdvisorPairComparator implements Comparator<Pair<Advisor, Student>>

{       
        @SuppressWarnings("rawtypes")
        public int compare(Pair a1, Pair a2) {
                if(((Advisor) a1.getF()).getName().equals(((Advisor) a2.getF()).getName()))
                return 0;
                else{
                        int ceil = (((Advisor) a1.getF()).getName().length()>(((Advisor)a2.getF()).getName().length())?((Advisor) a2.getF()).getName().length():((Advisor) a1.getF()).getName().length());
                       
                        for(int i=0; i < ceil; i++) {
                                char c1 = ((Advisor) a1.getF()).getName().charAt(i);
                                char c2 = ((Advisor) a2.getF()).getName().charAt(i);
                               
                                if(c1 != c2)
                                        return (c1<c2)?-1:1;
                        }
                       
                        return ((Advisor) a1.getF()).getName().length()>((Advisor) a2.getF()).getName().length()?1:-1;                       
                }
        }
       
}

---

I keep getting an error in the main class on the Collections.sort lines saying:

The method sort(List<T>, Comparator<? super T>) in the type Collections is not applicable for the arguments (ArrayList<Pair>, AdvisorPairComparator)

Any help would be greatly appreciated.

Thanks.

It will compile with these changes (plus some more)

Code:

---

        Collections.sort(list, new AdvisorPairComparator<Pair>());



 class AdvisorPairComparator<T> implements Comparator<T>{   
    @Override
    public int compare(T a1, T a2) {

---