All O`one Data Structure

class AllOne {

    /** Initialize your data structure here. */
    Map<String, Integer> map = new HashMap<>();
    public AllOne() {
        
    }
    
    /** Inserts a new key <Key> with value 1. Or increments an existing key by 1. */
    public void inc(String key) {
        map.put(key, map.getOrDefault(key, 0)+1);
    }
    
    /** Decrements an existing key by 1. If Key's value is 1, remove it from the data structure. */
    public void dec(String key) {
        if(map.containsKey(key) == false)
            return;
        map.put(key, map.get(key)-1);
        if(map.get(key)==0){
            map.remove(key);
        }
    }
    
    /** Returns one of the keys with maximal value. */
    public String getMaxKey() {
        if(map.size() == 0){
            return "";
        }
        String res = "";
        int min = Integer.MIN_VALUE;
        Iterator hmIterator = map.entrySet().iterator(); 
        while (hmIterator.hasNext()) { 
            Map.Entry mapElement = (Map.Entry)hmIterator.next(); 
            if((int)mapElement.getValue() >= min){
                res = (String)mapElement.getKey();
                min = (int)mapElement.getValue();
            } 
        } 
        return res;
    }
    
    /** Returns one of the keys with Minimal value. */
    public String getMinKey() {
        if(map.size() == 0){
            return "";
        }
        String res = "";
        int min = Integer.MAX_VALUE;
        Iterator hmIterator = map.entrySet().iterator(); 
        while (hmIterator.hasNext()) { 
            Map.Entry mapElement = (Map.Entry)hmIterator.next(); 
            if((int)mapElement.getValue() <= min){
                res = (String)mapElement.getKey();
                min = (int)mapElement.getValue();
            } 
        } 
        return res;
    }
}

/**
 * Your AllOne object will be instantiated and called as such:
 * AllOne obj = new AllOne();
 * obj.inc(key);
 * obj.dec(key);
 * String param_3 = obj.getMaxKey();
 * String param_4 = obj.getMinKey();
 */