I want to launch any one of the existing android applications (contacts, call dialer, etc.) from my app upon on click of a button.
All that I know is to get the Intent o
Intent launchIntent = getPackageManager().getLaunchIntentForPackage("com.package.address");
startActivity(launchIntent);
You don't really call another application - you generate the intent and then wait for someone to pick it up. Are you referring to Contact's app URL as "class path"? If so here's Contacts.Intents helper class reference that you can use to create Contacts intents
Here's a short example:
Intent intent = new Intent();
intent.setAction(Contacts.Intents.SHOW_OR_CREATE_CONTACT);