Question

Im trying to put arraylists into an arraylist. Adding data to the new arrays, then print them in order. Im only getting errors.

Is this the right way to create an arraylist in another arraylist using a for loop?

I would also like to now how I can get data from the array in a better way then these long expresions.

My errors

    jogging.java:101: warning: [unchecked] unchecked call to add(E) as a member of the raw type java.util.ArrayList
                res.get(iter).add(new Resultat(name,time));

   jogging.java:152: warning: [unchecked] unchecked conversion found   : java.util.ArrayList required: java.util.List<T> Collections.sort(res.get(iter2));

    jogging.java:152: warning: [unchecked] unchecked method invocation: <T>sort(java.util.List<T>) in java.util.Collections is applied to (java.util.ArrayList)
                Collections.sort(res.get(iter2));

    import java.util.;
    import java.lang.;


class Resultat implements Comparable<Resultat> {

    String namn;
    double tid;

    public Resultat( String n, double t ) {
        namn = n;
        tid = t;
    }
 public String toString() 
{
        return namn + " "+ tid;
    }

    public int compareTo( Resultat r ) {

        if (this.tid < r.tid){
        return -1;
        }
        else if (this.tid > r.tid){
                return 1;
                  }
        else if (this.tid == r.tid && this.namn.compareTo(r.namn) <= 0)
        {
            return -1;
        }
        else if ( this.tid == r.tid && this.namn.compareTo(r.namn) >= 0){
            return 1;
        }
        else {return 0;}


    }
}



public class jogging {

    public static void main( String[] args ){


        int runners = scan.nextInt();

        int competitions = scan.nextInt();

    //create arraylist with arraylists within
        ArrayList <ArrayList> res = new ArrayList<ArrayList>();
        for(int i = 0; i <= competitions; ++i){
        res.add(new ArrayList<Resultat>());
        }




        for (int i = 0; i < runners; i++){

            String name = scan.next();

        //runs the person made
        int antalruns = scan.nextInt();

        for(int n = 0; n <antalruns; n++){

            //number of the run
            int compnumber = scan.nextInt();
            //time for the run
            double time = scan.nextDouble();


            for(int iter = 0; iter < res.size(); ++iter){
                res.get(iter).add(new Resultat(name,time));
            }




                       }        
                 }




            for(int iter2 = 0; iter2 < res.size(); ++iter2) {
                Collections.sort(res.get(iter2));
                System.out.println(iter2);

                for(int it = 0; it < res.get(iter2).size(); ++it) {
                    System.out.println(res.get(iter2).get(it));
                }
            }


                }
                 }

Answer 1

The unchecked warnings are because you haven’t declared the generic types of the 2nd ArrayList. Try using

ArrayList <ArrayList<Resultat>> res = new ArrayList<ArrayList<Resultat>>();

Yes, it’s a bit tedious. 🙁

Also, most think it good practice to use the interface (e.g. List, not ArrayList) on the left side, just in case you change your mind as to the implementation in the future. e.g.

List <List<Resultat>> res = new ArrayList<ArrayList<Resultat>>();

ADDED

Also, you could simplify your compareTo() method. For comparing the tids, look at Double.compare(). Something like:

   public int compareTo( Resultat r ) {

      int compare = Double.compare(tid, r.tod);
      if (compare != 0)
         return compare;
      else
         return namn.compareTo(r.namn);
   }