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 {

    HashMap<Integer,Integer> map = new HashMap<Integer,Integer>();

    // Add the number to an internal data structure.
    public void add(int number)
    {
        if(map.containsKey(number)) map.put(number, map.get(number)+1);
        else map.put(number,1);

    }

    // Find if there exists any pair of numbers which sum is equal to the value.
    public boolean find(int value)
    {
        for(int key:map.keySet())
        {
            int num1 = key;
            int num2 = value - num1;
            if(num1==num2&&map.get(num1)>1) return true;
            else if(num1!=num2&&map.containsKey(num2)) return true;
        }
        return false;
    }
}