To save yourself the trouble of automatically removing entries from a hash table, Java supplies the WeakHashMap class. Investigate that class in the SDK documentation and rewrite WeakReferenceDemo ...

HashMap vs. Hashtable similarities Both the Hashtable and HashMap implement the Map interface and both share the same set of methods used to add, remove and manipulate elements of a key-value, ...

Seventy years after the invention of a data structure called a hash table, theoreticians have found the most efficient possible configuration for it.