java.lang.NullPointerException

Question

My code runs perfectly on my IDE but continues to throw a null pointer exception where ever I compare strings on the code challenge page. I need to compare strings to see if the user would like another go, although I also compare user input to make sure they have entered something. Any ideas?

package com.teamtreehouse;

import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader;

public class Main {

public static void main(String[] args) {
// write your code here
    Prompter prompter = new Prompter();
    BufferedReader yesNoReader = new BufferedReader(new InputStreamReader(System.in));
    String yesNo = "no";
    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);

    do{
        prompter.run(tmpl);
        System.out.printf("%n%nWould you like to have another go?  ");
        try {
            yesNo = yesNoReader.readLine();

        } catch (IOException e) {
            System.out.println("There was a problem with your answer");
            e.printStackTrace();
            System.exit(0);
        }
    }while(yesNo.compareToIgnoreCase("yes") == 0);
}

}

package com.teamtreehouse;

import java.io.*; 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);
    }
    //Print out the results that were gathered here by rendering the template
    System.out.printf("Your TreeStory:%n%n%s", tmpl.render(results));
}

/**
 * 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{

    String response = null;
   do {
        System.out.printf("Please give me a %s:  ", phrase);
        response = mReader.readLine();
    } while(mCensoredWords.contains(response) || response.isEmpty());

    return response;
}

}

Answer 1 · 2016-01-05T04:15:36Z

January 5, 2016 4:15am

After all the other stuff with the null values in the prompter and all that...I got to thinking about the response I got back from the challenge when I worked around the null values you kept getting. It kept coming back with no compiler errors, but it did ask you if you'd prompted the user for a new template String.

What if the reason you're getting a null value at the prompter is because he's testing a new string template with a different number of placeholders?

One of the errors you got was that it seemed to keep prompting the "user" (or the test code) for more words, and you got back a null response. This is to be expected if a readLine() is run on a stream that has reached its end.

One test, though, might assert that there are three placeholders to plug into a new template, but the hard-coded template string you have there is going to prompt for four -- every time.

Does your program prompt the user for a new template string so the test can customize it and run a test based on that? Or are you always using the default?

All I'm currently seeing is that you're doing prompter.run() on a single story String.

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);
    prompter.run(tmpl);

But step one is: The user is prompted for a new string template (the one with the double underscores in it)

Any chance you're not letting the test try out different template strings?

Answer 2 · 2016-01-04T15:52:23Z

January 4, 2016 3:52pm

Also, you might be triggering something weird with the way I am reading your output and providing your program input in the code challenge.

Why don't you try putting the loop in the Prompter.run method and not create another reader object and see if that does it for you.

Sorry for the weird environment :/

Answer 3 · 2016-01-05T01:54:44Z

January 5, 2016 1:54am

Thanks Gavin, Yes you are right. I have deleted that one from Main. Now just using the one in Prompter. Main is currently:

package com.teamtreehouse;

public class Main {

public static void main(String[] args) {
    // write your code here
    Prompter prompter = new Prompter();
    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);
    prompter.run(tmpl);

}

}

I believe the "no" at the end of: first prompt second prompt PASS_1 PASS_2 no, is the result of missing a null passed to the promptForAWord function:

public String promptForWord(String phrase) throws IOException {

    String response = "";
    do {
        System.out.printf("Please give me a %s:  ", phrase);
        response = mReader.readLine();
        if(response == null || response.isEmpty()){
            response = "noAnswer";
        }

    } while (mCensoredWords.contains(response) || response.compareToIgnoreCase("noAnswer") == 0);

    return response;
}

As such I am trying to write code that fits, although the above attempt throws this:

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space at java.util.Arrays.copyOf(Arrays.java:3236) at java.io.ByteArrayOutputStream.grow(ByteArrayOutputStream.java:118) at java.io.ByteArrayOutputStream.ensureCapacity(ByteArrayOutputStream.java:93) at java.io.ByteArrayOutputStream.write(ByteArrayOutputStream.java:153) at java.io.PrintStream.write(PrintStream.java:480) at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:221) at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:291) at sun.nio.cs.StreamEncoder.flushBuffer(StreamEncoder.java:104) at java.io.OutputStreamWriter.flushBuffer(OutputStreamWriter.java:185) at java.io.PrintStream.write(PrintStream.java:527) at java.io.PrintStream.print(PrintStream.java:669) at java.io.PrintStream.append(PrintStream.java:1065) at java.io.PrintStream.append(PrintStream.java:57) at java.util.Formatter$FixedString.print(Formatter.java:2595) at java.util.Formatter.format(Formatter.java:2508) at java.io.PrintStream.format(PrintStream.java:970) at java.io.PrintStream.printf(PrintStream.java:871) at com.teamtreehouse.Prompter.promptForWord(Prompter.java:97) at com.teamtreehouse.Prompter.promptForWords(Prompter.java:80) at com.teamtreehouse.Prompter.run(Prompter.java:44) at com.teamtreehouse.Main.main(Main.java:10) at JavaTester.run(JavaTester.java:77) at JavaTester.main(JavaTester.java:39)

What have I done?????

Answer 4 · 2016-01-05T02:43:22Z

January 5, 2016 2:43am

The pseudo tests do no match what is requested by the challenge:

This is essentially what I am testing

The user is prompted for a new string template (the one with the double underscores in it).

a. The prompter class has a new method that prompts for the story template, and that method is called.

The user is then prompted for each word that has been double underscored.

a. The answer is checked to see if it is contained in the censored words. User is continually prompted until they enter a valid word

The user is presented with the completed story

Not happy!!!!!!

Answer 5 · 2016-01-05T00:05:10Z

January 5, 2016 12:05am

Thanks for getting back to me Gavin and Craig. I tried changing my code to set the response to "no" if the response = null and that seems to have cleared the null exception.

if (response == null) { response = "no"; }

However, I was then given another fault, or rather was asked:

             "Did you prompt the user for a new story (1)? I see the original prompt".

So I then tried what Craig suggested and placed my loop in the run() function and recieved the same message and the following output:

Please give me a name: Please give me a adjective: Please give me a noun: Please give me a noun: Please give me a noun: Please give me a noun: Your TreeStory:

Thanks Testing first prompt and then second prompt for helping me out. You are really a PASS_1 PASS_2 and I owe you a no.

Would you like to try again?

It looks like the no was passed early? Is that possible?

My changed Main class:

package com.teamtreehouse;

import java.io.BufferedReader; import java.io.InputStreamReader;

public class Main {

public static void main(String[] args) {
    // write your code here
    Prompter prompter = new Prompter();
    BufferedReader yesNoReader = new BufferedReader(new InputStreamReader(System.in));
    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);
    prompter.run(tmpl);

}

}

My changed Prompter() class:

package com.teamtreehouse;

import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; 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;
    String response = null;

    do {

        try {
            results = promptForWords(tmpl);
        } catch (IOException e) {
            System.out.println("There was a problem prompting for words");
            e.printStackTrace();
            System.exit(0);
        }
        //Print out the results that were gathered here by rendering the template
        System.out.printf("Your TreeStory:%n%n%s", tmpl.render(results));
        //See if player would like another go
        System.out.println("\n\nWould you like to try again?  ");
        try {
            response = mReader.readLine();
            if (response == null) {
                response = "no";
            }
        } catch (IOException e) {
            System.out.println("There was a problem with your answer.");
            e.printStackTrace();
            System.exit(0);
        }

    } while (response.compareToIgnoreCase("yes") == 0);

}

/**
 * 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 {

    String response = null;
    do {
        System.out.printf("Please give me a %s:  ", phrase);
        response = mReader.readLine();
        if (response == null) {
            response = "no";
        }
    } while (mCensoredWords.contains(response));

    return response;
}

}

This does work in my IDE :)

Answer 6 · 2016-01-05T05:29:15Z

January 5, 2016 5:29am

Gavin you are the man!!! I don't know how I would have done without you. Thank you, thank you, thank you. I missed the new template thing completely. Just should have read the requirements. Cheers :)

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Patrick Allwood

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java.lang.NullPointerException

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Gavin Ralston

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6 Answers

Gavin Ralston

Gavin Ralston

What if the reason you're getting a null value at the prompter is because he's testing a new string template with a different number of placeholders?

Craig Dennis

Craig Dennis

Gavin Ralston

Gavin Ralston

Patrick Allwood

Patrick Allwood

Gavin Ralston

Gavin Ralston

Patrick Allwood

Patrick Allwood

This is essentially what I am testing

Patrick Allwood

Patrick Allwood

Gavin Ralston

Gavin Ralston

Patrick Allwood

Patrick Allwood

Gavin Ralston

Gavin Ralston