Parser

/**
* This class is part of the "World of Zuul" application.
* "World of Zuul" is a very simple, text based adventure game.
*
* This parser reads user input and tries to interpret it as an "Adventure"
* command. Every time it is called it reads a line from the terminal and
* tries to interpret the line as a two word command. It returns the command
* as an object of class Command.
*
* The parser has a set of known command words. It checks user input against
* the known commands, and if the input is not one of the known commands, it
* returns a command object that is marked as an unknown command.
*
* @author Ahmad Lamaul Farid
* @version 12 November 2020
*/

import java.util.Scanner;
public class Parser
{
    private CommandWords commands; // holds all valid command words
    private Scanner reader; // source of command input

    /**
    * Create a parser to read from the terminal window.
    */
    public Parser()
    {
        commands = new CommandWords();
        reader = new Scanner(System.in);
    }

    /**
    * @return The next command from the user.
    */
    public Command getCommand()
    {
        String inputLine; // will hold the full input line
        String word1 = null;
        String word2 = null;

        System.out.print("> "); // print prompt

        inputLine = reader.nextLine();

        // Find up to two words on the line.
        Scanner tokenizer = new Scanner(inputLine);
        if(tokenizer.hasNext())
        {
            word1 = tokenizer.next(); // get first word
            if(tokenizer.hasNext())
            {
                word2 = tokenizer.next(); // get second word
                // note: we just ignore the rest of the input line.
            }
        }

        // Now check whether this word is known. If so, create a command
        // with it. If not, create a "null" command (for unknown command).
        if(commands.isCommand(word1))
        {
            return new Command(word1, word2);
        }
        else
        {
            return new Command(null, word2);
        }
    }
}