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Java

Posted by Jeremy Bobbin
Jeremy Bobbin
25,481 Points

Why am I getting a NullPointerException when I use System.console().readLine()?

This is with regards to the "TreeStory" coding challenge in Java - local development environments.

package com.teamtreehouse;

import java.io.IOException; import java.util.Arrays; import java.util.List;

public class Main {

public static void main(String[] args) {
// write your code here
    // TODO:csd - Instantiate a new Prompter object and prompt for the story template
    Prompter prompter = new Prompter();
    List<String> results;
    String story = "Thanks __name__ for helping me out.  You are really a __adjective__ __noun__ and I owe you a __noun__.";
    Template tmpl = new Template(story);
    // TODO:csd - Use the prompter object to have it do the prompting, censoring and outputting.  Call Prompter.run
    prompter.run(tmpl);
    try {
        results = prompter.promptForWords(tmpl);
        String treeStory = tmpl.render(results);
        System.out.printf("Your TreeStory:%n%n%s", treeStory);
    } catch (IOException e) {
        e.printStackTrace();
    }
    // TODO:csd - This should really happen in the Prompter.run method, let's get these implementation details out of the main method

}

}

package com.teamtreehouse;

import java.util.ArrayList; import java.util.List; import java.util.regex.Matcher; import java.util.regex.Pattern;

public class Template { /** * The string format that is waiting to receive values */ private String mCompiled; private List<String> mPlaceholders;

/**
 * @param text A template with double underscored surrounded placeholders. eg: Hello __name__!
 */
public Template(String text) {
    // Match on double underscore surrounded words, like __name__ or __proper noun__
    Pattern pattern = Pattern.compile("__([^__]+)__");
    Matcher matcher = pattern.matcher(text);
    mPlaceholders = new ArrayList<String>();
    while (matcher.find()) {
        String label = matcher.group(1);
        mPlaceholders.add(label);
    }
    mCompiled = matcher.replaceAll("%s");
}


/**
 * @return Ordered names of placeholders in the template
 */
public List<String> getPlaceHolders() {
    return mPlaceholders;
}


/**
 * Given a list of values, replaces the fill in the blanks in order.
 *
 * @param values The replacements for the fill in the blank
 * @return The filled out TreeStory
 */
public String render(List<String> values) {
    // String.format accepts the templates and Object... (a variable amount of objects)
    return String.format(mCompiled, values.toArray());
}

}

package com.teamtreehouse;

import java.io.*; import java.io.IOException; import java.nio.file.Files; import java.nio.file.Path; import java.nio.file.Paths; import java.util.ArrayList; import java.util.HashSet; import java.util.List; import java.util.Set;

public class Prompter { private BufferedReader mReader; private Set<String> mCensoredWords;

public Prompter() {
    mReader = new BufferedReader(new InputStreamReader(System.in));
    loadCensoredWords();
}

private void loadCensoredWords() {
    mCensoredWords = new HashSet<String>();
    Path file = Paths.get("resources", "censored_words.txt");
    List<String> words = null;
    try {
        words = Files.readAllLines(file);
    } catch (IOException e) {
        System.out.println("Couldn't load censored words");
        e.printStackTrace();
    }
    mCensoredWords.addAll(words);
}

public void run(Template tmpl) {
    List<String> results = null;
    try {
        results = promptForWords(tmpl);
    } catch (IOException e) {
        System.out.println("There was a problem prompting for words");
        e.printStackTrace();
        System.exit(0);
    }
    // TODO:csd - Print out the results that were gathered here by rendering the template
    try {
        System.out.printf("%s", tmpl.render(promptForWords(tmpl)));
    } catch (IOException e) {
        e.printStackTrace();
    }

}

/**
 * Prompts user for each of the blanks
 *
 * @param tmpl The compiled template
 * @return
 * @throws IOException
 */
public List<String> promptForWords(Template tmpl) throws IOException {
    List<String> words = new ArrayList<String>();
    for (String phrase : tmpl.getPlaceHolders()) {
        String word = promptForWord(phrase);
        words.add(word);
    }
    return words;
}


/**
 * Prompts the user for the answer to the fill in the blank.  Value is guaranteed to be not in the censored words list.
 *
 * @param phrase The word that the user should be prompted.  eg: adjective, proper noun, name
 * @return What the user responded
 */

public String promptForWord(String phrase) throws IOException {
    // TODONE:csd - Prompt the user for the response to the phrase, make sure the word is censored, loop until you get a good response.
    System.out.printf("Please give me a %s", phrase);
    String word = System.console().readLine();
    boolean isBadWord = mCensoredWords.contains(word);
    do {
        if (isBadWord) {
            System.out.printf("The word, %s, is not allowed. Please try again with a different %s:  ", phrase);
            word = System.console().readLine();
        }
    } while(isBadWord);
    return word;
}

}