1. The key difference: Access to the Hashtable is synchronized on the table while access to the HashMap isn't. You can add it, but it isn't there by default.
2. Iterator in the HashMap is fail-safe while the enumerator for the Hashtable isn't. If you change the map while iterating, you'll know.
3. HashMap permits null values in it, while Hashtable doesn't.
Model–view–controller (MVC) is an architectural pattern used in software engineering. The pattern isolates business logic from input and presentation, permitting independent development, testing and maintenance of each.
An MVC application is a collection of model/view/controller triplets (a central dispatcher is often used to delegate controller actions to a view-specific controller). Each model is associated with one or more views (projections) suitable for presentation (not necessarily visual presentation). When a model changes its state, it notifies its associated views so they can refresh. The controller is responsible for initiating change requests and providing any necessary data inputs to the model.
MVC is frequently and needlessly convoluted by tying it directly to a graphical user interface. That a controller is often driven indirectly from a GUI is incidental. Likewise, rendering views graphically is an application of MVC, not part of the pattern definition. A business-to-business interface can leverage an MVC architecture equally well.
