1import java.nio.file.*;
2import java.io.IOException;
3import java.util.List;
4 
5public class ShoppingFile {
6    public static void main(String[] args) throws IOException {
7        Path p = Path.of("shopping.txt");
8        Files.write(p, List.of("Atta 10kg", "Mustard oil", "Tomatoes 2kg", "Tea pack"));
9        List<String> items = Files.readAllLines(p);
10        for (int i = 0; i < items.size(); i++) System.out.println((i + 1) + ") " + items.get(i));
11        System.out.println("File size: " + Files.size(p) + " bytes");
12    }
13}

1import java.time.*;
2import java.time.temporal.ChronoUnit;
3 
4public class Countdown {
5    public static void main(String[] args) {
6        LocalDate today = LocalDate.of(2026, 10, 26);
7        String[] names = {"Chhath Puja", "Christmas", "Republic Day"};
8        LocalDate[] dates = {LocalDate.of(2026, 11, 15), LocalDate.of(2026, 12, 25), LocalDate.of(2027, 1, 26)};
9        for (int i = 0; i < names.length; i++) {
10            System.out.printf("%-13s %s (%s) in %d days%n", names[i], dates[i], dates[i].getDayOfWeek(), ChronoUnit.DAYS.between(today, dates[i]));
11        }
12    }
13}

1import java.time.*;
2 
3public class AgeCheck {
4    public static void main(String[] args) {
5        LocalDate on = LocalDate.of(2026, 10, 26);
6        String[] n = {"Priya", "Kunal", "Meera"};
7        LocalDate[] born = {LocalDate.of(2008, 10, 26), LocalDate.of(2008, 10, 27), LocalDate.of(1995, 2, 14)};
8        for (int i = 0; i < n.length; i++) {
9            Period p = Period.between(born[i], on);
10            System.out.printf("%-6s %2d y %2d m %2d d -> %s%n", n[i], p.getYears(), p.getMonths(), p.getDays(), p.getYears() >= 18 ? "eligible" : "not eligible");
11        }
12    }
13}

1import java.nio.file.*;
2import java.io.IOException;
3import java.util.*;
4 
5public class AttendanceLog {
6    public static void main(String[] args) throws IOException {
7        Path p = Path.of("attendance.txt");
8        Files.deleteIfExists(p);
9        String[][] days = {{"2026-10-20", "Aman,Riya,Sana"}, {"2026-10-21", "Aman,Sana"}, {"2026-10-22", "Aman,Riya,Imran"}};
10        for (String[] d : days) {
11            Files.writeString(p, d[0] + ":" + d[1] + "\n", StandardOpenOption.CREATE, StandardOpenOption.APPEND);
12        }
13        Map<String, Integer> present = new TreeMap<>();
14        for (String line : Files.readAllLines(p)) {
15            for (String name : line.split(":")[1].split(",")) present.merge(name, 1, Integer::sum);
16        }
17        System.out.println(present);
18    }
19}

1import java.time.*;
2import java.time.format.DateTimeFormatter;
3 
4public class FeeDue {
5    static LocalDate due(LocalDate month) {
6        LocalDate d = month.withDayOfMonth(10);
7        return d.getDayOfWeek() == DayOfWeek.SUNDAY ? d.plusDays(1) : d;
8    }
9    public static void main(String[] args) {
10        DateTimeFormatter f = DateTimeFormatter.ofPattern("dd MMM yyyy EEE");
11        LocalDate m = LocalDate.of(2026, 11, 1);
12        LocalDate[] paid = {LocalDate.of(2026, 11, 9), LocalDate.of(2026, 12, 12), LocalDate.of(2027, 1, 11), LocalDate.of(2027, 2, 10)};
13        for (int i = 0; i < 4; i++) {
14            LocalDate d = due(m.plusMonths(i));
15            boolean late = paid[i].isAfter(d);
16            System.out.println("Due " + d.format(f) + " | paid " + paid[i].format(f) + (late ? " | late fee Rs 50" : " | on time"));
17        }
18    }
19}

1import java.nio.file.*;
2import java.io.IOException;
3import java.util.*;
4 
5public class ReportWriter {
6    public static void main(String[] args) throws IOException {
7        List<String> lines = Files.readAllLines(Path.of("marks.csv"));
8        StringBuilder out = new StringBuilder(String.format("%-8s %5s %6s %s%n", "Name", "Total", "Pct", "Grade"));
9        int count = 0;
10        for (String line : lines.subList(1, lines.size())) {
11            String[] f = line.split(",");
12            int t = 0;
13            for (int i = 1; i < f.length; i++) t += Integer.parseInt(f[i].trim());
14            double pct = t / 3.0;
15            String g = pct >= 90 ? "A+" : pct >= 75 ? "A" : pct >= 60 ? "B" : "C";
16            out.append(String.format("%-8s %5d %5.1f%% %s%n", f[0], t, pct, g));
17            count++;
18        }
19        Files.writeString(Path.of("report.txt"), out);
20        System.out.println("Report written for " + count + " students");
21    }
22}

1import java.nio.file.*;
2import java.io.IOException;
3import java.time.*;
4import java.time.format.DateTimeFormatter;
5 
6public class EmiSchedule {
7    public static void main(String[] args) throws IOException {
8        double p = 85000, r = 10.5 / 12 / 100; int n = 6;
9        double emi = p * r * Math.pow(1 + r, n) / (Math.pow(1 + r, n) - 1);
10        DateTimeFormatter f = DateTimeFormatter.ofPattern("dd-MM-yyyy");
11        StringBuilder csv = new StringBuilder("date,emi,interest,principal,balance\n");
12        LocalDate d = LocalDate.of(2026, 11, 5);
13        double bal = p;
14        for (int i = 0; i < n; i++, d = d.plusMonths(1)) {
15            double in = bal * r, pr = emi - in;
16            bal -= pr;
17            System.out.printf("%s EMI %.0f int %6.0f prin %7.0f bal %7.0f%n", d.format(f), emi, in, pr, Math.abs(bal));
18            csv.append(String.format("%s,%.2f,%.2f,%.2f,%.2f%n", d.format(f), emi, in, pr, Math.abs(bal)));
19        }
20        Files.writeString(Path.of("emi.csv"), csv);
21    }
22}

1import java.io.*;
2import java.nio.file.*;
3import java.time.LocalDateTime;
4import java.time.format.DateTimeFormatter;
5import java.util.*;
6 
7public class LogAnalyser {
8    public static void main(String[] args) throws IOException {
9        DateTimeFormatter f = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
10        Map<String, Integer> levels = new TreeMap<>();
11        Map<Integer, Integer> perHour = new TreeMap<>();
12        List<String> errors = new ArrayList<>();
13        try (BufferedReader r = Files.newBufferedReader(Path.of("server.log"))) {
14            String line;
15            while ((line = r.readLine()) != null) {
16                LocalDateTime t = LocalDateTime.parse(line.substring(0, 16), f);
17                String level = line.split(" ")[2];
18                levels.merge(level, 1, Integer::sum);
19                perHour.merge(t.getHour(), 1, Integer::sum);
20                if (level.equals("ERROR")) errors.add(t.toLocalTime() + " " + line.substring(23));
21            }
22        }
23        System.out.println("Levels: " + levels);
24        int busy = Collections.max(perHour.entrySet(), Map.Entry.comparingByValue()).getKey();
25        System.out.println("Busiest hour: " + busy + ":00 (" + perHour.get(busy) + " lines)");
26        errors.forEach(e -> System.out.println("ERROR at " + e));
27    }
28}

1import java.nio.file.*;
2import java.io.IOException;
3import java.time.*;
4import java.time.format.DateTimeFormatter;
5import java.time.temporal.ChronoUnit;
6import java.util.*;
7 
8record Issue(String member, String book, LocalDate issued) {
9    LocalDate due() { return issued.plusDays(14); }
10}
11 
12public class DueTracker {
13    public static void main(String[] args) throws IOException {
14        DateTimeFormatter f = DateTimeFormatter.ofPattern("dd-MM-yyyy");
15        LocalDate today = LocalDate.of(2026, 10, 26);
16        List<Issue> issues = new ArrayList<>();
17        for (String l : Files.readAllLines(Path.of("issued.csv"))) {
18            String[] p = l.split(",");
19            issues.add(new Issue(p[0], p[1], LocalDate.parse(p[2], f)));
20        }
21        StringBuilder out = new StringBuilder("member,book,due,daysLate,fine\n");
22        int totalFine = 0;
23        for (Issue i : issues) {
24            long late = ChronoUnit.DAYS.between(i.due(), today);
25            if (late > 0) {
26                int fine = (int) Math.min(late * 2, 60);
27                totalFine += fine;
28                out.append(String.join(",", i.member(), i.book(), i.due().format(f), String.valueOf(late), String.valueOf(fine))).append("\n");
29                System.out.printf("%-6s %-16s due %s, %2d days late, fine Rs %d%n", i.member(), i.book(), i.due().format(f), late, fine);
30            }
31        }
32        Files.writeString(Path.of("overdue.csv"), out);
33        System.out.println("Total fines: Rs " + totalFine);
34    }
35}

1import java.nio.file.*;
2import java.io.IOException;
3import java.time.*;
4import java.util.*;
5 
6public class OpenHours {
7    static Set<LocalDate> holidays = new HashSet<>();
8    static boolean between(LocalTime t, String a, String b) { return !t.isBefore(LocalTime.parse(a)) && t.isBefore(LocalTime.parse(b)); }
9    static String status(LocalDateTime dt) {
10        if (holidays.contains(dt.toLocalDate())) return "closed (holiday)";
11        if (dt.getDayOfWeek() == DayOfWeek.TUESDAY) return "closed (weekly off)";
12        LocalTime t = dt.toLocalTime();
13        if (between(t, "09:00", "13:00") || between(t, "14:00", "20:30")) return "OPEN";
14        return between(t, "13:00", "14:00") ? "lunch break" : "closed (outside hours)";
15    }
16    public static void main(String[] args) throws IOException {
17        for (String s : Files.readAllLines(Path.of("holidays.txt"))) holidays.add(LocalDate.parse(s.trim()));
18        String[] orders = {"2026-10-26T10:15", "2026-10-26T13:20", "2026-10-27T11:00", "2026-11-08T12:00", "2026-10-29T20:45", "2026-10-30T19:59"};
19        for (String o : orders) {
20            LocalDateTime dt = LocalDateTime.parse(o);
21            System.out.printf("%s %-9s -> %s%n", o.replace('T', ' '), dt.getDayOfWeek(), status(dt));
22        }
23    }
24}

1public class TwoThreads {
2    public static void main(String[] args) throws InterruptedException {
3        Runnable r = () -> {
4            for (int i = 1; i <= 3; i++) {
5                System.out.println(Thread.currentThread().getName() + " -> " + i);
6                try { Thread.sleep(50); } catch (InterruptedException e) { }
7            }
8        };
9        Thread a = new Thread(r, "Alpha"), b = new Thread(r, "Beta");
10        a.start(); b.start();
11        a.join(); b.join();
12        System.out.println("Both threads done");
13    }
14}

1public class Countdown {
2    public static void main(String[] args) throws InterruptedException {
3        Thread timer = new Thread(() -> {
4            for (int s = 5; s >= 1; s--) {
5                System.out.println("  timer: " + s);
6                try { Thread.sleep(120); } catch (InterruptedException e) { return; }
7            }
8        });
9        timer.start();
10        Thread.sleep(30);
11        System.out.println("main: loading questions...");
12        timer.join();
13        System.out.println("Start the exam!");
14    }
15}

1class Account {
2    private int balance = 0;
3    synchronized void deposit(int amt) { balance += amt; }
4    int getBalance() { return balance; }
5}
6 
7public class SharedAccount {
8    public static void main(String[] args) throws InterruptedException {
9        Account acc = new Account();
10        Runnable atm = () -> { for (int i = 0; i < 10000; i++) acc.deposit(1); };
11        Thread a = new Thread(atm), b = new Thread(atm);
12        a.start(); b.start();
13        a.join(); b.join();
14        System.out.println("Final balance: " + acc.getBalance());
15    }
16}