cs106a – Assignment #4 – Task #1

The complete specification of assignment #4 can be found as part of the stream at iTunes.

Playing a console-based game

In the first part of this assignment, your job is to write a program that handles the user interaction component of the game—everything except the graphical display. To solve the problem, your program must be able to:

  • Choose a random word to use as the secret word. That word is chosen from a word list, as described in the following paragraph.
  • Keep track of the user’s partially guessed word, which begins as a series of dashes and then updated as correct letters are guessed.
  • Implement the basic control structure and manage the details (ask the user to guess a letter, keep track of the number of guesses remaining, print out the various messages, detect the end of the game, and so forth).


The only operation that is beyond your current knowledge is that of representing the list of words from which you can choose a word at random. For the first two parts of the assignment, you will simply make use of a class that we’ve given you called HangmanLexicon that provides a small list of words that will allow you to test your program. (A lexicon is very much like a dictionary, but does not necessarily include definitions, which makes it a more appropriate name for a class that provides a list of words with no associated meanings.) The implementation of the class you’ve been given is only a temporary expedient to make it possible to code the rest of the assignment. In Part III, you will replace the definition we’ve provided with one that reads a list of words from a data file.
The strategy of creating a temporary implementation that provides enough functionality to implement the rest of the program is a common technique in programming. Such temporary implementations are usually called stubs. In this assignment, the starter project comes with a stub implementation of the HangmanLexicon class. The class contains two public methods: getWordCount(), which returns the number of words in the lexicon, and getWord(i), which returns the word at index i. Like all indices in Java, the value i runs from 0 to one less than the number of words.
A game that used this implementation of the HangmanLexicon class would quickly become uninteresting because there are only ten words available. Even so, it will allow you to develop the rest of the program and then come back and improve this part later.
Part I is a string manipulation problem using the methods developed in Chapter 8. The sample runs in Figure 1 should be sufficient to illustrate the basic operation of the game, but the following points may help to clarify a few issues:

  • At the beginning of your run method, you need to create a new HangmanLexicon and store it in an instance variable. If you extend the program to allow the user to play multiple games, the creation of the HangmanLexicon should be performed outside the loop that plays the game repeatedly so that this operation is performed once rather than for every game.
  • You should accept the user’s guesses in either lower or upper case, even though all letters in the secret words are written in upper case.
  • If the user guesses something other than a single letter, your program should tell the user that the guess is illegal and accept a new guess.
  • If the user guesses a correct letter more than once, your program should simply do nothing. Guessing an incorrect letter a second time should be counted as another wrong guess. (In each case, these interpretations are the easiest way to handle the situation, and your program will probably do the right thing even if you don’t think about these cases in detail.)

Start by getting the lexicon and use a random generator together with the number of available words to get a word (which is stored in an instance variable). A second instance variable holds the currently guessed word, which consists only of dashes for now. While the game has not been won or lost, print the current guessed word, together with the status of available guesses, and ask for a guess. If the input from the user has more than one character or is no character at all, continue asking for a new guess.

If the guess was correct, check in addition if the complete word has been uncovered, if not reduce the count of available guesses.

    public void run() {
		println("Welcome to Hangman!");
		
		HangmanLexicon lexicon = new HangmanLexicon();
		RandomGenerator rgen = RandomGenerator.getInstance();
		
		wordToGuess = lexicon.getWord(rgen.nextInt(lexicon.getWordCount()));
		currentWord = dashifyWord();
		int numberOfGuesesLeft = 8;

		boolean gameWon = false;
		while (!gameWon && (numberOfGuesesLeft > 0)) {
			println("The word now looks like this: " + currentWord);
			println("You have " + numberOfGuesesLeft + " guesses left.");
			String guessInput = readLine("Your guess: ");
			char guess = guessInput.charAt(0);
			if ((guessInput.length() > 1) || !Character.isLetter(guess)) {
				println("Please enter single letters only!");
				continue;			
			}
			if (guessCorrect(guess)) {
				println("That guess is correct.");
				if (wordToGuess.equals(currentWord)) {
					gameWon = true;
				}
			} else  {
				println("There are no " + guess + "'s in the word.");
				numberOfGuesesLeft--;
			}						
		}
		
		if (gameWon) {
			println("You guessed the word: " + wordToGuess);
			println("You win.");			
		} else {
			println("You are completely hung.");
			println("The word was: " + wordToGuess);
			println("You lose.");
		}
			
	}

To get the initial dashed word just create a new string with the length of the word consisting only of dashes:

    private String dashifyWord() {
    	String result = "";
    	for(int i = 0 ; i < wordToGuess.length(); i++) {
    	      result += "-";
    	   }
    	   return result;
    }

To check if the guess is correct loop over all characters of the word. If the current character equals the guess, use that character, otherwise use the character of the previously dashed/solved word to create a new string. If at least one character matched copy that new string to the solved word string:

    private boolean guessCorrect(char guess) {
    	guess = Character.toUpperCase(guess);
    	boolean guessCorrect = false;
    	String newWord = "";
    	for (int i = 0; i < wordToGuess.length(); i++) {
    		if (wordToGuess.charAt(i) == guess) {
    			newWord += guess;
    			guessCorrect = true;
    		} else {
    			newWord += currentWord.charAt(i);
    		}
    	}
    	if (guessCorrect) {
    		currentWord = new String(newWord);
    	}
    	return guessCorrect;
    }

The code for this assignment is available on github.

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