String command = "";
String parameter = "";
Scanner dataIn = new Scanner(System.in);

while (!command.equals("exit")) {
    System.out.print(">> ");

    command = dataIn.next().trim();
    parameter = dataIn.next().trim();
    //should ^ these have error handling?

    if (command.equals("dothis")) {
        //do this w/ parameter..
    } else if (command.equals("dothat")) {
        //do that w/ parameter..
    } //else if... {}
      else {
        system.out.println("Command not valid.");
    }
}

System.out.println("Program exited by user.");

Scanner sc = new Scanner(System.in);

for (prompt(); sc.hasNextLine(); prompt()) {

    String line = sc.nextLine().replaceAll("n", "");

    // return pressed
    if (line.length == 0)
        continue;

    // split line into arguments
    String[] args = line.split(" ");

    // process arguments
    if (args.length == 1) {
        if (args[0].equalsIgnoreCase("exit"))
            System.exit(0);
        if (args[0].equalsIgnoreCase("dosomething"))
            // do something
    } else if (args.length == 2) {
        // do stuff with parameters
    }
}