Two Sum III - Data structure design

Design and implement a TwoSum class. It should support the following operations: add and find.

add - Add the number to an internal data structure.
find - Find if there exists any pair of numbers which sum is equal to the value.

For example,
add(1); add(3); add(5);
find(4) -> true
find(7) -> false

public class TwoSum {

    // Add the number to an internal data structure.

    private Map <Integer, Integer> map;

    public TwoSum(){
        map = new HashMap();
    }

    public void add(int number) {
       map.put(number, map.get(number) == null ? 1 : 2);
    }

    // Find if there exists any pair of numbers which sum is equal to the value.
    public boolean find(int value) {

        for(Map.Entry<Integer, Integer> entry : map.entrySet()){
            int key = entry.getKey(), val = entry.getValue();
            if(map.get(value - key) != null && (value != key * 2 || val > 1)){
                return true;
            }
        }
        return false;
    }
}