Practice Questions — File Handling in Java

import java.io.*;

public class WordCounter {
    public static void main(String[] args) {
        // Create test file
        try (PrintWriter pw = new PrintWriter("sample.txt")) {
            pw.println("Hello World");
            pw.println("Java is great");
            pw.println("File handling rocks");
        } catch (FileNotFoundException e) {
            System.out.println("Cannot create file");
            return;
        }

        int lines = 0, words = 0, chars = 0;
        try (BufferedReader br = new BufferedReader(new FileReader("sample.txt"))) {
            String line;
            while ((line = br.readLine()) != null) {
                lines++;
                chars += line.length();
                String[] tokens = line.trim().split("\\s+");
                if (!tokens[0].isEmpty()) {
                    words += tokens.length;
                }
            }
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
            return;
        }
        System.out.println("Lines: " + lines);
        System.out.println("Words: " + words);
        System.out.println("Characters: " + chars);
    }
}

import java.io.*;

public class CSVProcessor {
    public static void main(String[] args) {
        // Create input file
        try (PrintWriter pw = new PrintWriter("students.csv")) {
            pw.println("Arjun,85,92,78");
            pw.println("Sneha,35,28,42");
            pw.println("Vikram,91,88,95");
        } catch (FileNotFoundException e) {
            return;
        }

        try (
            BufferedReader br = new BufferedReader(new FileReader("students.csv"));
            PrintWriter pw = new PrintWriter(new FileWriter("results.csv"))
        ) {
            String line;
            while ((line = br.readLine()) != null) {
                String[] parts = line.split(",");
                String name = parts[0];
                try {
                    int m1 = Integer.parseInt(parts[1]);
                    int m2 = Integer.parseInt(parts[2]);
                    int m3 = Integer.parseInt(parts[3]);
                    double avg = (m1 + m2 + m3) / 3.0;
                    String status = avg >= 40 ? "PASS" : "FAIL";
                    pw.printf("%s,%d,%d,%d,%.1f,%s%n", name, m1, m2, m3, avg, status);
                } catch (NumberFormatException e) {
                    System.out.println("Invalid data for: " + name);
                }
            }
            System.out.println("Results written to results.csv");
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

import java.io.*;

public class FileSearch {
    public static void main(String[] args) {
        try (PrintWriter pw = new PrintWriter("article.txt")) {
            pw.println("Programming is fun.");
            pw.println("Java is a popular language.");
            pw.println("Python is also widely used.");
            pw.println("Many companies use both.");
            pw.println("Java supports OOP and multithreading.");
        } catch (FileNotFoundException e) {
            return;
        }

        String keyword = "Java";
        int lineCount = 0, totalOccurrences = 0;
        try (BufferedReader br = new BufferedReader(new FileReader("article.txt"))) {
            String line;
            int lineNum = 0;
            while ((line = br.readLine()) != null) {
                lineNum++;
                String lowerLine = line.toLowerCase();
                String lowerKey = keyword.toLowerCase();
                int index = 0;
                int count = 0;
                while ((index = lowerLine.indexOf(lowerKey, index)) != -1) {
                    count++;
                    index += lowerKey.length();
                }
                if (count > 0) {
                    lineCount++;
                    totalOccurrences += count;
                    System.out.println("Line " + lineNum + ": " + line);
                }
            }
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
            return;
        }
        System.out.println("Found " + totalOccurrences + " occurrences in " + lineCount + " lines.");
    }
}

import java.nio.file.*;
import java.io.IOException;
import java.util.*;
import java.util.stream.*;

public class FileMerger {
    public static void main(String[] args) throws IOException {
        Path file1 = Paths.get("file1.txt");
        Path file2 = Paths.get("file2.txt");
        Path merged = Paths.get("merged.txt");

        Files.write(file1, List.of("Hello", "World"));
        Files.write(file2, List.of("Java", "Rocks"));

        List<String> mergedLines = new ArrayList<>();

        try (Stream<String> lines = Files.lines(file1)) {
            lines.map(line -> "[file1.txt] " + line)
                 .forEach(mergedLines::add);
        }
        try (Stream<String> lines = Files.lines(file2)) {
            lines.map(line -> "[file2.txt] " + line)
                 .forEach(mergedLines::add);
        }

        Files.write(merged, mergedLines);

        System.out.println("Merged file contents:");
        Files.readAllLines(merged).forEach(System.out::println);

        Files.deleteIfExists(file1);
        Files.deleteIfExists(file2);
        Files.deleteIfExists(merged);
    }
}

import java.io.*;
import java.util.*;

public class LogAnalyzer {
    public static void main(String[] args) {
        try (PrintWriter pw = new PrintWriter("app.log")) {
            pw.println("INFO: Server started");
            pw.println("WARN: Low memory detected");
            pw.println("ERROR: NullPointerException in UserService");
            pw.println("INFO: Request processed successfully");
            pw.println("ERROR: Connection timeout to database");
            pw.println("INFO: Scheduled task completed");
            pw.println("WARN: Deprecated API usage");
        } catch (FileNotFoundException e) {
            return;
        }

        Map<String, Integer> counts = new LinkedHashMap<>();
        counts.put("INFO", 0);
        counts.put("WARN", 0);
        counts.put("ERROR", 0);
        List<String> errors = new ArrayList<>();

        try (BufferedReader br = new BufferedReader(new FileReader("app.log"))) {
            String line;
            while ((line = br.readLine()) != null) {
                int colonIndex = line.indexOf(':');
                if (colonIndex == -1) continue;
                String level = line.substring(0, colonIndex).trim();
                String message = line.substring(colonIndex + 1).trim();
                counts.merge(level, 1, Integer::sum);
                if ("ERROR".equals(level)) {
                    errors.add(message);
                }
            }
        } catch (IOException e) {
            System.out.println("Read error: " + e.getMessage());
            return;
        }

        try (PrintWriter pw = new PrintWriter("report.txt")) {
            pw.println("=== Log Analysis Report ===");
            pw.println();
            for (Map.Entry<String, Integer> entry : counts.entrySet()) {
                pw.printf("%-8s: %d%n", entry.getKey(), entry.getValue());
            }
            pw.println();
            pw.println("Error Details:");
            for (int i = 0; i < errors.size(); i++) {
                pw.printf("  %d. %s%n", i + 1, errors.get(i));
            }
            System.out.println("Report written to report.txt");
        } catch (FileNotFoundException e) {
            System.out.println("Write error: " + e.getMessage());
        }
    }
}