Non Unique Numbers

Find Non Unique Numbers from an given array.
Exp : [1,3,1,4,5,6,3,2 ] in this array [1,3] are non unique number.

public class NonUniqueNumbers  {

public static void main(String[] args) {
List<Integer> list = Arrays.asList(1,3,1,4,5,6,3,2);
System.out.println(getCount(list));
}

private static int getCount(List<Integer> numbers) {
int result = 0;
    Map<Integer, Integer> numberMap = new HashMap<>();
    for(int i=0;i<numbers.size();i++){
        if(numberMap.containsKey(numbers.get(i))){
            numberMap.put(numbers.get(i), numberMap.get(numbers.get(i))+1);
        }else{
        numberMap.put(numbers.get(i), 1);
        }
    }
    for(Map.Entry<Integer, Integer> mp:numberMap.entrySet()){
        if((int)mp.getValue() > 1){
            result++;
        }
    }
    return result;
}

}