How to do command constraints in a menu system

So I have this Finch robot and I've been creating a menu system for it. I would like to make the system such that it has certain constraints. Here is my code:

import javax.swing.JOptionPane;
import edu.cmu.ri.createlab.terk.robot.finch.Finch;


public class RobotController 
	{
		private static Finch myf = null;
		public static void main(String args[])
		{	
			myf = new Finch(); // Object
			String c = "";
			do
			{
				c = FinchController();

				if (c == "Forward") MoveForward(c);
				if (c=="Back")MoveBack(c);
				if (c == "Left Turn") MoveLeft(c);
				if (c == "Right Turn") MoveRight(c);
				if (c == "Nose Colour") GreenLED(c);
				if (c == "Three Point Turn") ThreePointTurn(c);
				//if (c == "Input Command File")InputCommandFile(c);
			}
				while (c != "End Program");
				myf.quit();
			} 
private static String FinchController()
		{
			Object[] possibilities = {"Forward","Left Turn","Right Turn", "Nose Colour" ,"Three Point Turn","Input Command File","End Program"};
			String c = (String)JOptionPane.showInputDialog(null,"Robot Controller \n\nChoose a command:\n\n","Robot Controller",JOptionPane.PLAIN_MESSAGE, null,possibilities,"Forward");
			if (c == null || c.length() == 0) c = "Quit";return(c);
			}

I've posted the menu system as you can see. An example of a constraint I want to add is say the user selects the "Forward" command and this executes, then directly after the user selects "Forward" again, I want to make this give an error, so that a "Fowarward" command cannot be chose directly after a "Forward" command.

I've been thinking of if statements but I'm really stuck. Your help is greatly appreciated.