Regards

There is no class which can directly solve your problem. But you can achieve what you are looking for by using HashSet.

Make your own class which as a key , value as its member variable. Implement its override its default equals and hashCode methods. And store the object of this class in your HashSet class.

The java.util.Hashtable and friends will let you have only one entry for any given key, but it does not allow multiple values for the same key, directly.

You could build your own dfata structure to do this, which is basically a hashtable of lists:

Hashtable:
Key Value
key1 list [value1, value2, value3]
key2 list [value1, valud2, value3]
key3 list [value1, valud2, value3]

Then, when you perform an 'insert', you can scan the list in the table for your key and see if the new value already exists. If it does, either throw an exception or do nothing or whatever you want to do.

If you're really paranoid, you could use a Set instead of a List to store your values.

Hope that helps,

-chris