can i wire the dishwasher and the garbage disposal together
Together? You'll have to explain what you mean by that. If you mean, 'on the same circuit', then often you can. There are valid reasons not to do so, but it is okay for most equipment when you use a 20 amp circuit. It depends in large part on the data plate amp draw of the dish machine. Post the proposed dish machine's amp draw, and someone will give you your yes/no. We're looking for a dish machine with an amp draw of less than 10 amps.
Originally Posted by TonyD
..and is it better to have a switch for the disposal or not.
That's a design issue that's totally up to you. The code does not require a switch, per se. You may want one, however. If you do not install a swtich for the disposer, you'll have to crawl under the sink and plug in the disposer each time you want to use it. That's not the most convenient arrangement.