import java.util.*;

class Commands {
  public static final Map<String,Runnable> lookup = Collections.unmodifiableMap(new HashMap<String,Runnable>(){{
   put("quit", new Runnable() { @Override public void run() { quit(); } });
   put("calc", new Runnable() { @Override public void run() { calc(); } });
   put("foo",  new Runnable() { @Override public void run() { foo();  } });
  }});
}

//Usage

final Commands c = new Commands();
final Runnable cmd = c.lookup(argument);
if(cmd != null) cmd.run();
else sendMessageToUserThatArgumentDoesntExist