I have a problem and any help would be greatly appreciated!

I have hashtable like that:
Hashtable category = new Hashtable();

category.put("XREF_STATE_CODE", "Global Setup");
category.put("XREF_STATE_COUNTRY", "Global Setup");
category.put("PROPERTY_CONTACT", "Property Setup");
category.put("PROPERTY_DESC", "Property Setup");
category.put("RENTABLE_GROUP", "Property Setup");
category.put("RENTABLE_DAY", "Property Setup");
category.put("HMA_STATEMENT", "Invoicing");
category.put("RA_TRANSACTION", "Invoicing");
category.put("RA_INVOICE", "Invoicing");
category.put("INVOICE_COMMENT", "Invoicing");

where key is table_name and value is a category which each table_name related
to. Knowing table_name I can easily to get value(category). The problem is
how knowing category(value of hashtable) to get table_names (keys) that related
to this category.
Thanks in advance.