public HashMap() 
{
         super();
}

 public HashMap(int initialCapacity) 
{
        super(initialCapacity);
}

 public HashMap(Map t) 
{
        super(t);
}

 public HashMap(int initialCapacity,
    float loadFactor) 
{
        super(initialCapacity, loadFactor);
}

 public Object get(Object key,
    Object _default) 
{
        if (this.containsKey(key)) {
            return this.get(key);
        } else {
            return _default;
        }
}

Get method extended by default object to be returned when key is not found.