Tool Setup

ExprTool.java

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+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.util.Scanner;
+
+import org.antlr.v4.runtime.*;
+import org.antlr.v4.runtime.tree.*;
+import org.antlr.v4.runtime.misc.ParseCancellationException;
+
+public class ExprTool {
+    public static void main(String[] args) throws Exception {
+        if (args.length == 0) {
+            // If no files given then read from stdin
+            Scanner scanner = new Scanner(System.in);
+            StringBuilder inputBuilder = new StringBuilder();
+            while (scanner.hasNextLine()) {
+                inputBuilder.append(scanner.nextLine()).append("\n");
+            }
+            scanner.close();
+
+            parseAndWalk(inputBuilder.toString(), "<stdin>");
+        } else {
+            // for Loop through all given file paths 
+            for (String filePath : args) {
+                try {
+                    String inputText = new String(Files.readAllBytes(Paths.get(filePath)));
+                    parseAndWalk(inputText, filePath);
+                } catch (IOException e) {
+                    System.err.println("Error reading file: " + filePath);
+                }
+            }
+        }
+    }
+
+    // Reusable parsing + walking
+    private static void parseAndWalk(String inputText, String sourceName) {
+        try {
+            // Create char stream
+            CharStream input = CharStreams.fromString(inputText, sourceName);
+
+            // Lexer
+            ExprLexer lexer = new ExprLexer(input);
+            lexer.removeErrorListeners();
+            lexer.addErrorListener(new ThrowingErrorListener());
+
+            // Tokens
+            CommonTokenStream tokens = new CommonTokenStream(lexer);
+
+            // Parser
+            ExprParser parser = new ExprParser(tokens);
+            parser.removeErrorListeners();
+            parser.addErrorListener(new ThrowingErrorListener());
+
+            // Parse compilation unit
+            ParseTree tree = parser.compilationUnit();
+
+            // Walk
+            ParseTreeWalker walker = new ParseTreeWalker();
+            walker.walk(new ClassPrinter(sourceName), tree);
+
+        } catch (RuntimeException e) {
+            System.err.println("Parsing failed: " + e.getMessage());
+        }
+    }
+
+    // Listener to print class declarations with line/column
+    public static class ClassPrinter extends ExprParserBaseListener {
+        private final String sourceName;
+
+        public ClassPrinter(String sourceName) {
+            this.sourceName = sourceName;
+        }
+
+        @Override
+        public void enterClassDeclaration(ExprParser.ClassDeclarationContext ctx) {
+            int line = ctx.getStart().getLine();
+            int col = ctx.getStart().getCharPositionInLine();
+            String className = ctx.identifier().getText();
+            System.out.printf("Class %s, file %s, line %d, column %d%n",
+                              className, sourceName, line, col);
+        }
+    }
+
+    // Custom error listener
+    public static class ThrowingErrorListener extends BaseErrorListener {
+        @Override
+        public void syntaxError(Recognizer<?, ?> recognizer,
+                                Object offendingSymbol,
+                                int line, int charPositionInLine,
+                                String msg,
+                                RecognitionException e) {
+            String sourceName = recognizer.getInputStream().getSourceName();
+            if (sourceName == null || sourceName.isEmpty()) {
+                sourceName = "<unknown>";
+            }
+
+            String formatted = String.format(
+                " file %s, line %d, column %d%n%s",
+                sourceName, line, charPositionInLine, msg
+            );
+
+            throw new ParseCancellationException(formatted);
+        }
+    }
+}

Test/BadTaxApp.java

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+package Test
+
+abstract class TaxCalculator {
+    protected double income
+
+    public TaxCalculator(double income {
+        this.income = income
+    }
+    public abstract double calculateTax()
+
+    public double afterTaxIncome() {
+        return income - calculateTax()
+    
+}
+class FlatTaxCalculator extends TaxCalculator {
+    private static final double RATE = 0.15
+    public FlatTaxCalculator(double income) super(income)
+    public double calculateTax() {
+        return income * RATE
+    }
+
+public class TaxApp {
+    static class BracketTaxCalculator extends TaxCalculator {
+        public BracketTaxCalculator(double income) 
+            super(income)
+
+        public double calculateTax() {
+            if (income <= 10000) return income * 0.10
+            else if (income <= 50000) return (10000 * 0.10) + ((income - 10000) * 0.20)
+            else return (10000 * 0.10) + (40000 * 0.20) + ((income - 50000) * 0.30)
+        }
+    }
+
+    public static void main(String[] args) {
+        double income = 60000
+
+        TaxCalculator flat = new FlatTaxCalculator(income)
+        double flatTax = flat.calculateTax()
+        double flatAfterTax = flat.afterTaxIncome()
+
+        TaxCalculator bracket = new BracketTaxCalculator(income)
+        double bracketTax = bracket.calculateTax()
+        double bracketAfterTax = bracket.afterTaxIncome()
+    }
+}

Test/TaxApp.java

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+package Test;
+abstract class TaxCalculator {
+    protected double income;
+
+    public TaxCalculator(double income) {
+        this.income = income;
+    }
+    public abstract double calculateTax();
+    public double afterTaxIncome() {
+        return income - calculateTax();
+    }
+}
+class FlatTaxCalculator extends TaxCalculator {
+    private static final double RATE = 0.15;
+    public FlatTaxCalculator(double income) {super(income);}
+    public double calculateTax() {
+        return income * RATE;
+    }
+}
+
+public class TaxApp {
+    static class BracketTaxCalculator extends TaxCalculator {
+        public BracketTaxCalculator(double income) {
+            super(income);
+        }
+        public double calculateTax() {
+            if (income <= 10000) {return income * 0.10;} 
+            else if (income <= 50000) { return (10000 * 0.10) + ((income - 10000) * 0.20);}
+            else { return (10000 * 0.10) + (40000 * 0.20) + ((income - 50000) * 0.30);}
+        }
+    }
+
+    public static void main(String[] args) {
+        double income = 60000;
+
+        TaxCalculator flat = new FlatTaxCalculator(income);
+        double flatTax = flat.calculateTax();
+        double flatAfterTax = flat.afterTaxIncome();
+
+        TaxCalculator bracket = new BracketTaxCalculator(income);
+        double bracketTax = bracket.calculateTax();
+        double bracketAfterTax = bracket.afterTaxIncome();
+    }
+}