چند نکته در مورد Collection- map در جاوا

1. map stores the data  (key, value) pair
2. map does not support duplicate key
3. key can not but value can be duplicate
4. map hs two implemented clases 1-hash map 2-hash table
   
   • hash map: this store the element in (key, value) pair and allows null values
   • hash map is not synchronized by default
   • Hash table: this doesn't allow any null value and it is synchronized by default