The java.util.Dictionary class in Java is an abstract class that represents a collection of key-value pairs. It is similar to a Map collection but with a more limited functionality. It was part of the original Java collections framework, but has been largely replaced by the more versatile HashMap and Hashtable classes.

The Dictionary class is implemented as a hash table with keys and values stored as Object types. It provides methods to add, retrieve, and remove key-value pairs, as well as methods to get the number of entries in the dictionary, and to check if it is empty.

One of the limitations of the Dictionary class is that it only supports keys and values of type Object. This means that if you want to store values of a specific type, you will need to cast them back to their original type when you retrieve them from the dictionary.

Another limitation is that it does not support null keys or values. If you try to add a null key or value, the dictionary will throw a NullPointerException.

In summary, while the Dictionary class is still available in Java, it is generally recommended to use the more versatile HashMap or Hashtable classes instead.