I have a program that asks the user 10 political questions and determines which party they belong to with probability calculations based off previous survey answers stored in txt files.
Whenever I run this right after I enter an answer for the first question, I get an exception that says the return value of “java.util.Map.get(Object)” is null.
public static void main(String[] args) {
Map<PoliticalParty, ProbabilityManager> probabilityManagerMap = new HashMap<>();
probabilityManagerMap.put(PoliticalParty.REPUBLICAN, new ProbabilityManager(PoliticalParty.REPUBLICAN, 0.25));
probabilityManagerMap.put(PoliticalParty.DEMOCRAT, new ProbabilityManager(PoliticalParty.DEMOCRAT, 0.25));
probabilityManagerMap.put(PoliticalParty.SOCIALIST, new ProbabilityManager(PoliticalParty.SOCIALIST, 0.25));
probabilityManagerMap.put(PoliticalParty.LIBERTARIAN, new ProbabilityManager(PoliticalParty.LIBERTARIAN, 0.25));
Map<String, Integer> answerNumbers = new HashMap<>();
answerNumbers.put("a", 1);
answerNumbers.put("b", 2);
answerNumbers.put("c", 3);
Survey survey = new Survey();
SurveyUserInput userInputCheck = new SurveyUserInput(answerNumbers);
String userInput = "";
Map<Integer, Integer> answerIndices = new HashMap<>();
ProbabilityCalculator cal = new ProbabilityCalculator(probabilityManagerMap);
int answerNumber = 0;
SurveyManager.printProb(probabilityManagerMap);
for(int i = 0; i<survey.surveyComponentArray.length; i++) {
SurveyComponent c = survey.getQuestion(i);
answerNumber = userInputCheck.performSurvey(i, c);
answerIndices.put(i, answerNumber);
cal.recalculate(i, answerNumber); //this is the problem. When I comment this out, its fine.
}
public class SurveyUserInput {
Map<String, Integer> mapKey;
public SurveyUserInput(Map<String, Integer> mapKey) {
this.mapKey = mapKey;
}
Scanner scanner = new Scanner(System.in);
Survey survey = new Survey();
public int performSurvey(int questionNumber, SurveyComponent com) {
String user = "";
//for(int i = 0; i<survey.surveyComponentArray.length; i++) {
int a;
System.out.println(com.question);
for(String answer : com.getAnswers()) {
System.out.println(answer);
}
do {
user = scanner.next().toLowerCase();
} while(!user.equals("a") && !user.equals("b") && !user.equals("c"));
a = mapKey.get(user);
return a;
}
public class SurveyComponent {
String question;
String[] answers;
SurveyComponent(String question, String...answers) {
this.question = question;
this.answers = answers;
}
public String[] getAnswers() {
return answers;
}
}
public class Survey {
SurveyComponent[] surveyComponentArray;
public Survey() {
surveyComponentArray = new SurveyComponent[10];
surveyComponentArray[0] = new SurveyComponent("How do you feel about the issue of guns?",
"A) I believe in the 2nd Amendment completely.", "B) I believe in gun control",
"C) I don't care");
surveyComponentArray[1] = new SurveyComponent("How do you feel about the USA's involvement in with other nations?",
"A) I believe we should focus on America.", "B) I believe we need to be involved.",
"C) I don't even believe in foregin aid.");
surveyComponentArray[2] = new SurveyComponent("How do you feel about Climate Change?",
"A) I don't think its a big deal its not like its the end of the world.", "B) I believe its literally the end of the world.",
"C) I think its a concern.");
surveyComponentArray[3] = new SurveyComponent("How do you feel about Marxism?",
"A) I greatly admire it.", "B) I don't admire it",
"C) I don't care");
surveyComponentArray[4] = new SurveyComponent("Do you believe in capitalism?",
"A) Yes.", "B) No, I think it should be relplaced with a more socailly equitable system",
"C) I don't care");
surveyComponentArray[5] = new SurveyComponent("How do you feel about taxes?",
"A) I believe taxes should be lowered.", "B) I think they should be raised to fund social programs.",
"C) I don't think we should have to pay taxes.");
surveyComponentArray[6] = new SurveyComponent("How do you feel about the government's part in our lives?",
"A) I believe the government should play an active role.", "B) I wish the government would just leave me alone.",
"C) I believe in small government.");
surveyComponentArray[7] = new SurveyComponent("How do you feel about incarceration and law enforcement?",
"A) I believe prisons and law enforcement should be dimantled and abolished.", "B) I believe in criminal justice reform",
"C) I believe in having prisions and law enforcement.");
surveyComponentArray[8] = new SurveyComponent("How do you feel about laws banning things such as drugs?",
"A) I believe there need to be some laws. Such as banning drugs.", "B) I believe everyone is capable of making their own choices",
"C) I believe no one should be in prison for just using drugs.");
surveyComponentArray[9] = new SurveyComponent("How do you feel about funding welfare?",
"A) I believe welfare should be funded a lot.", "B) I believe welfare should not be funded",
"C) I don't care");
}
public SurveyComponent getQuestion(int index) {
return surveyComponentArray[index];
}
}
public class ProbabilityCalculator {
private final Map<PoliticalParty, ProbabilityManager> partyMap;
public ProbabilityCalculator(Map<PoliticalParty, ProbabilityManager> partyMap) {
this.partyMap = partyMap;
}
public void recalculate(int questionNumber, int answerNumber) {
double totalProb = 0;
Map<PoliticalParty, Double> probOfAnswerGivenParty = new HashMap<>();
for(PoliticalParty party : PoliticalParty.values()) {
ProbabilityManager probManager = partyMap.get(party); //The error says the error apperently lies somewhere in here.
if(probManager != null) {
double probOfAnsGivenP = probManager.calculateProbOfAnswerGivenParty(questionNumber, answerNumber);
totalProb += probManager.getProbability() * probOfAnsGivenP;
probOfAnswerGivenParty.put(party, probOfAnsGivenP);
} else {
System.out.println("no");
}
}
for(PoliticalParty party : PoliticalParty.values()) {
ProbabilityManager probManager = partyMap.get(party);
double probOfPartyGivenANS = probManager.getProbability() * probOfAnswerGivenParty.get(party) / totalProb;
probManager.setProbability(probOfPartyGivenANS);
}
}
}
public class ProbabilityManager {
public PoliticalParty party;
private double partyProbability;
private String fileName;
private Map<Integer, Integer> previousSurveyData;
public ProbabilityManager(PoliticalParty party, double partyProbability) {
this.party = party;
this.partyProbability = partyProbability;
this.fileName = party.name().toLowerCase();
previousSurveyData = SurveyFileIO.readFromFile(fileName);
}
public void setProbability(double partyProbability) {
this.partyProbability = partyProbability;
}
public double getProbability() {
return partyProbability;
}
public double calculateProbOfAnswerGivenParty(int questionNumber, int answerNumber) {
int counter = 0;
if(previousSurveyData.get(questionNumber) == answerNumber) {
counter++;
} else {
return 1.0;
}
return (double)counter / previousSurveyData.size();
}
public void saveAnswerIndices(Map<Integer, Integer> answerIndices) {
for(Map.Entry<Integer, Integer> entry : answerIndices.entrySet()) {
int key = entry.getKey();
int value = entry.getValue();
this.previousSurveyData.put(key, value);
}
SurveyFileIO.writeToFile(fileName, previousSurveyData);
}
}
This is the enum
public enum PoliticalParty {
REPUBLICAN,
DEMOCRAT,
LIBERTARIAN,
SOCIALIST
}
This is the error: Exception in thread “main” java.lang.NullPointerException: Cannot invoke “java.lang.Integer.intValue()” because the return value of “java.util.Map.get(Object)” is null
at ProbabilityManager.calculateProbOfAnswerGivenParty(ProbabilityManager.java:28)
at ProbabilityCalculator.recalculate(ProbabilityCalculator.java:22)
at Main.main(Main.java:39)
I cannot figure this out. I know this is a lot of code, but I’m at a loss.
I’ve been trying different error handling methods but nothing works. I would REALLY APPRICIATE some help.
Thanks!
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