Java Code question... getting error that says I am using the wrong arguments for my method but they look to be the same?

Question

I am getting this error, "The method mergeSort(java.util.ArrayList) in the type Preferences is not applicable for the arguments (java.util.ArrayList)Java(67108979)" on my code ( I will paste below). But to me it looks like the exact same method so I am confused as to what is wrong.

The error occurs in preferenceSimilarity on the two lines where I try to call mergeSort.

import java.util.*;



public class Preferences<T>{
    //Combine the two ArrayLists
    private ArrayList<T> merge(ArrayList<T> left, ArrayList<T> right){
        ArrayList<T> result= new ArrayList<T>();
        int i=0; int j=0;
        while ((i< left.size()) && (j<right.size())){
            if (left.get(i).equals(right.get(j))){
                result.add(left.get(i));
                i++;
                j++;
            }
            else if(left.get(i).hashCode()< right.get(j).hashCode()){
                i++;
            }
            else{
                j++;
            }
        }
        return result;
    }

//MERGE SORT
public ArrayList<T> mergeSort(ArrayList<T> list1){
    if (list1.size()<=1){
        return list1;
    }

    int mid= list1.size()/2;
    ArrayList<T> left= new ArrayList<T>(list1.subList(0,mid));
    ArrayList<T> right = new ArrayList<T>(list1.subList(mid,list1.size()));

    left= mergeSort(left);
    right= mergeSort(right);

    return merge(left, right);
}

public static <T> double preferenceSimilarity(ArrayList<T> list1, ArrayList<T> list2){
   ** ArrayList<T> sorted1= mergeSort((ArrayList<T>) list1); //INCOMPATIBLE TYPES?? 
    ArrayList<T> sorted2= mergeSort((ArrayList<T>) list2);**

    double similarity= 0.0;
    int i=0;
    int j=0;
    while (i < sorted1.size() && j < sorted2.size()) {
        if (sorted1.get(i).equals(sorted2.get(j))) {
            similarity++;
            i++;
            j++;
        } else if (sorted1.get(i).hashCode() < sorted2.get(j).hashCode()) {  //HashCode returns integer value
            i++;
        } else {
            j++;
        }
    }

    double totalLen= Math.max(sorted1.size(),sorted2.size());
    return (similarity/totalLen);
 }

}

I tried to type cast them and that did nothing. I also tried to switch around my argument types but that didn't work because I need my solution to handle the generic types.

Answer 1

As the commenters have said, this is because you are calling a non-static from a static. Sadly that is not the error message, probably because of the generic type.

Create an instance as follows and call the methods non-statically:

public static <T> double preferenceSimilarity(ArrayList<T> list1, ArrayList<T> list2){
    Preferences<T> preferencesInstance = new Preferences<T>();
    ArrayList<T> sorted1= preferencesInstance.mergeSort((ArrayList<T>) list1);
    ArrayList<T> sorted2= preferencesInstance.mergeSort((ArrayList<T>) list2);