ArrayList warning- warning: [unchecked] unchecked call to add(E), also file will not run

Question

I've been trying to get this code to work for what feels like an age at this stage. it is meant to compute prime numbers in a range, and I've written a method to print them. Unfortunately the code will not compile, citing the warning:

"warning: [unchecked] unchecked call to add(E) as a member of the raw type java.util.List"

--I understand from googling that this warning is for not declaring what types of values should be in your erray, but I have done this, and the error only seems to come about when I try to use the .add() function on my array list.

and when I try to run it it gives a somewhat more scary error of "Static Error: Undefined name 'PrimeNumbers'

I think I've gone code-blind at this point and despite several attempts cannot find out what I am doing wrong.

import java.util.*;

public class PrimeNumbers { 

    private List listOfPrimeNumbers;  //add a member variable for the ArrayList
    public static void main(String args []){    
      PrimeNumbers primeNumberList = new PrimeNumbers(50);
      primeNumberList.print();  //use our new print method
    }

public PrimeNumbers (int initialCapacity) {
    listOfPrimeNumbers = new ArrayList<Integer>(initialCapacity/2);  //initialCapacity/2 is an easy (if not tight) upper bound
    long numberOfPrimes = 0; //Initialises variable numberOfPrimes to 0
    int start = 2;
    boolean[] isPrimeNumber = new boolean[initialCapacity + 1];

    for (int i=0;i==initialCapacity;i++) {//setting all values in array of booleans to true
    isPrimeNumber[i] = true;
    }
     while (start != initialCapacity)
        {
          if (isPrimeNumber[start])
          {
            listOfPrimeNumbers.add(start);
            //add to array list
            numberOfPrimes++;
            for (int i = start; start < initialCapacity; i+=start)
            {
              isPrimeNumber[i] = false;
            }
          }
          start++;
        }
    }

 public void print()  //add this printout function
 {
     int i = 1; 
     Iterator iterator = listOfPrimeNumbers.listIterator();
     while (iterator.hasNext())
     {
          System.out.println("the " + i + "th prime is: " + iterator.next());
          i++;
     }
     //or just System.out.println(listOfPrimeNumbers);, letting ArrayList's toString do the work.  i think it will be in [a,b,c,..,z] format
 }

 public List getPrimes() {return listOfPrimeNumbers;} //a simple getter isnt a bad idea either, even though we arent using it yet
}

Answer 1

Change this line

private List listOfPrimeNumbers;  //add a member variable for the ArrayList

to

private List<Integer> listOfPrimeNumbers;  //add a member variable for the ArrayList

This will elimiate the warning.

---

Bonus - you may want to use the enhanced for loop inside the print method as an alternative approach:

public void print() {
  int i = 1; 
  for (Integer nextPrime:listOfPrimeNumbers) {
      System.out.println("the " + i + "th prime is: " + nextPrime);
      i++;
  }
}