Parser.java

/*
 * NOTE:  You should not have to change this class unless you are adding more command words
 *        or something else more advanced.
 * This parser reads user input and tries to interpret it as a 
 * 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.
 */

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

class Parser 
{

    private CommandWords commands;  // holds all valid command words

    public Parser() 
    {
        commands = new CommandWords();
    }

    public Command getCommand() 
    {
        String inputLine = "";   // will hold the full input line
        String word1;
        String word2;

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

        BufferedReader reader = 
            new BufferedReader(new InputStreamReader(System.in));
        try {
            inputLine = reader.readLine();
        }
        catch(java.io.IOException exc) {
            System.out.println ("There was an error during reading: "
                                + exc.getMessage());
        }

        StringTokenizer tokenizer = new StringTokenizer(inputLine);

        if(tokenizer.hasMoreTokens())
            word1 = tokenizer.nextToken();      // get first word
        else
            word1 = null;
        if(tokenizer.hasMoreTokens())
            word2 = tokenizer.nextToken();      // get second word
        else
            word2 = null;

        // 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);
    }

    /**
     * Print out a list of valid command words.
     */
    public void showCommands()
    {
        commands.showAll();
    }
}