PLEASE FIX THIS ERROR IN THE CODE PLEASE: Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.util.List.iterator()" because the return value of "java.util.Map.get(Object)" is null at CFGSimplifier.simplifyEpsilonRules(CFGSimplifier.java:78) at CFGSimplifier.main(CFGSimplifier.java:16)

CHECK IF IT WORK BY USING A TXT FILE WITH THE FOLLOWING IN IT:

S-AaB|aaB

A-0

B-baA|0

THE EXPECTED ASWER SHOULD BE:

S-aB|aaB|a|aa

B-ba

import java.io.BufferedReader; import java.io.FileReader; import java.util.*; import java.io.*;

public class CFGSimplifier {

public static void main(String[] args) throws IOException { Scanner scanner = new Scanner(System.in); System.out.println("Enter a text file: "); String filePath = scanner.nextLine(); scanner.close();

Map> productions = readCFGFromFile(filePath);

simplifyEpsilonRules(productions); simplifyUselessRules(productions);

printSimplifiedCFG(productions); }

private static Map> readCFGFromFile(String filePath) throws IOException { Map> productions = new HashMap<>(); try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) { String line; while ((line = reader.readLine()) != null) { String[] rule = line.split("-"); String lhs = rule[0].trim(); String[] rhsList = rule[1].trim().split("\\|"); List rhs = new ArrayList<>(Arrays.asList(rhsList)); productions.put(lhs, rhs); } } return productions; }

private static void simplifyEpsilonRules(Map> productions) { Set epsilonProducibleVariables = new HashSet<>(); do { epsilonProducibleVariables.clear(); for (Map.Entry> entry : productions.entrySet()) { String variable = entry.getKey(); List variableProductions = entry.getValue();

if (variableProductions.contains("0")) { epsilonProducibleVariables.add(variable); }

for (String production : variableProductions) { for (char symbol : production.toCharArray()) { if (Character.isUpperCase(symbol) && productions.containsKey(String.valueOf(symbol))) { List epsilonProductions = productions.get(String.valueOf(symbol)); if (epsilonProductions != null) { for (String epsilonProduction : epsilonProductions) { if (epsilonProducibleVariables.contains(String.valueOf(symbol))) { epsilonProducibleVariables.add(variable); break; } } } } } } }

for (Map.Entry> entry : productions.entrySet()) { String variable = entry.getKey(); List variableProductions = entry.getValue(); List newProductions = new ArrayList<>();

for (String production : variableProductions) { if (!production.equals("0")) { newProductions.add(production); }

for (String otherProduction : productions.get(production)) { if (!newProductions.contains(otherProduction)) { newProductions.add(variable + otherProduction); } } } productions.put(variable, newProductions); }

} while (!epsilonProducibleVariables.isEmpty()); }

private static void simplifyUselessRules(Map> productions) { Set reachableVariables = new HashSet<>(); Set terminals = new HashSet<>();

Queue queue = new LinkedList<>(); queue.add("S"); // Assuming S is the start variable

while (!queue.isEmpty()) { String variable = queue.poll(); reachableVariables.add(variable);

for (String production : productions.getOrDefault(variable, Collections.emptyList())) { for (char symbol : production.toCharArray()) { if (Character.isUpperCase(symbol) && !reachableVariables.contains(String.valueOf(symbol))) { queue.add(String.valueOf(symbol)); } else if (Character.isLowerCase(symbol)) { terminals.add(String.valueOf(symbol)); } } } }

Set uselessVariables = new HashSet<>(productions.keySet()); uselessVariables.removeAll(reachableVariables); for (String variable : uselessVariables) { productions.remove(variable); }

// Remove productions containing useless terminals for (Map.Entry> entry : productions.entrySet()) { List variableProductions = entry.getValue(); variableProductions.removeIf(production -> { for (char symbol : production.toCharArray()) { if (Character.isLowerCase(symbol) && !terminals.contains(String.valueOf(symbol))) { return true; } } return false; }); } }

private static void printSimplifiedCFG(Map> productions) { for (Map.Entry> entry : productions.entrySet()) { String variable = entry.getKey(); List variableProductions = entry.getValue(); System.out.print(variable + " - "); System.out.println(String.join(" | ", variableProductions)); } } }