Full Case Studies

06 — Extended Portfolio

A full rundown of what each project actually does — the mechanics, the data handling, and the details that don't fit on the homepage cards.

Featured / 001

Java Battle Game

A two-player turn-based battle game with attack, defend, and heal mechanics, a coin betting pot, and randomized critical hits. Each action triggers its own sound effect, played on a background thread so the game never stalls.

Java OOP Multithreading Game Logic

⚙️ Key Features

Interactive two-player turn-based combat driven entirely by user input
Attack deals randomized damage with a 20% chance of a critical hit (2× damage)
Defend halves incoming damage for one turn, then resets
Heal restores HP up to the max, capped at 3 uses per player
A coin betting pot is settled once a winner is decided
Every action — attack, heal, invalid input, victory — triggers its own sound effect on a background thread

📚 What I Learned

Managing player state (HP, defending flag, heal count) with parallel arrays
Structuring a game loop with while and switch-case for player actions
Using static final constants for fixed values like MAX_HP and MAX_HEAL
Running sound playback on a separate thread so it never blocks the game loop
Integrating an external library (JLayer) for MP3 playback

Project1.java

import java.io.FileInputStream;
import java.util.Random;
import java.util.Scanner;

import javazoom.jl.player.Player;

public class Project1 {

    static final int MAX_HP = 100;
    static final int MAX_HEAL = 3;

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Random r = new Random();

        int[] hp = { MAX_HP, MAX_HP };
        boolean[] defending = { false, false };
        int[] healcount = { 0, 0 };
        String[] p = new String[2];

        int current = 0;

        System.out.print("Enter Player 1 Name: ");
        p[0] = sc.nextLine();
        playSound("rizz-sound-effect.mp3");

        System.out.print("Enter Player 2 Name: ");
        p[1] = sc.nextLine();
        playSound("rizz-sound-effect.mp3");

        int total = getBet(sc, p[0]) + getBet(sc, p[1]);

        while (hp[0] > 0 && hp[1] > 0) {
            int opponent = 1 - current;

            displayStatus(p, hp, defending, healcount);

            System.out.println("\n" + p[current] + "'s Turn");
            System.out.println("1. Attack  2. Defend  3. Heal");

            int choice = sc.nextInt();

            switch (choice) {
            case 1:
                attack(r, p, hp, defending, current, opponent);
                break;

            case 2:
                defending[current] = true;
                System.out.println(p[current] + " is defending!");
                break;

            case 3:
                heal(r, p, hp, healcount, current);
                break;

            default:
                System.out.println("Invalid choice!");
                playSound("vine-boom.mp3");
                continue;
            }

            if (hp[opponent] <= 0)
                break;

            current = opponent;
        }

        System.out.println("\n===== GAME OVER =====");
        if (hp[0] <= 0) {
            System.out.println(p[1] + " Wins!");
        } else {
            System.out.println(p[0] + " Wins!");
        }
        playSound("rizz-sound-effect.mp3");
        System.out.println("CONGRALUTIONS YOU WIN ￥" + total);

    }

    static void attack(Random r, String[] p, int[] hp, boolean[] defending, int current, int opponent) {
        int damage = r.nextInt(11) + 10;
        if ((r.nextInt(2) == 0)) {
            playSound("重いキック1.mp3");
        } else {
            playSound("punch-gaming-sound-effect-hd_RzlG1GE.mp3");
        }

        if (r.nextInt(100) < 20) {
            damage *= 2;
            System.out.println("🔥 CRITICAL HIT!");
            playSound("bone-crack.mp3");
        }

        if (defending[opponent]) {
            damage /= 2;
            defending[opponent] = false;
            playSound("rizz-sound-effect.mp3");
        }

        hp[opponent] -= damage;
        System.out.println(p[current] + " attacked for " + damage + " damage!");
    }

    static void heal(Random r, String[] p, int[] hp, int[] healcount, int current) {
        if (healcount[current] >= MAX_HEAL) {
            System.out.println("❌ No heals left!");
            playSound("fahhhhhhhhhhhhhh.mp3");
            return;
        }

        int heal = r.nextInt(20) + 5;
        hp[current] = Math.min(MAX_HP, hp[current] + heal);
        healcount[current]++;

        playSound("anime-wow-sound-effect.mp3");
        System.out.println(p[current] + " healed " + heal + " HP!");
    }

    static int getBet(Scanner sc, String player) {
        System.out.print(player + ", enter your bet: ");
        int bet = sc.nextInt();

        if (bet < 1000) {
            playSound("999-social-credit-siren.mp3");
        } else {
            playSound("anime-wow-sound-effect.mp3");
        }

        return bet;
    }

    static void displayStatus(String[] p, int[] hp, boolean[] defending, int[] healcount) {
        for (int i = 0; i < 2; i++) {
            System.out.println(p[i] + " HP: " + hp[i] +
                    (defending[i] ? " (Defending)" : "") +
                    " | Heals left: " + (MAX_HEAL - healcount[i]));
        }
    }

    static void playSound(String fileName) {
        new Thread(() -> {
            try {
                FileInputStream file = new FileInputStream(fileName);
                Player sound = new Player(file);
                sound.play();
            } catch (Exception e) {
                System.out.println("⚠ Sound error: " + fileName);
            }
        }).start();
    }
}

011

Expense Tracker

A console-based personal finance tool for logging daily spending. Add, delete, and search expenses by year, month, or category, with every record persisted to a CSV file and totals calculated on demand.

Java File I/O CSV ArrayList

⚙️ Key Features

Add an expense with amount, category, date, and note — IDs auto-increment from existing records
View every expense as an aligned table in the console
Delete an expense by ID, rewriting the CSV without that row
Search expenses by year, month, or category
Calculate and display the running total across all expenses
Data survives between sessions in a plain CSV file (Expensesdb.csv)

📚 What I Learned

Splitting responsibilities across Manager, Database, and Model classes
Reading and writing structured data to a CSV file with BufferedReader/FileWriter
Rebuilding a file's contents in place to support deletion by ID
Filtering an ArrayList of objects by year, month, or category

Project2.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.ArrayList;
import java.util.Scanner;

public class Project2 {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        ViewScreen view = new ViewScreen();
        ExpensesManager em = new ExpensesManager();

        while (true) {
            System.out.println("\n1.Add New Expenses");
            System.out.println("2.Show All Expenses");
            System.out.println("3.Delete Expense");
            System.out.println("4.Search");
            System.out.println("5.Show Total Amount");
            System.out.println("6.Exit");
            System.out.println("Enter the number: ");

            int menu = sc.nextInt();
            sc.nextLine();

            if (menu == 1) {

                System.out.println("Enter the Amount");
                double amount = sc.nextDouble();
                sc.nextLine();

                System.out.println("Enter the category");
                String category = sc.nextLine();

                System.out.println("Enter the date (yyyy-MM-dd)");
                String date = sc.nextLine();

                System.out.println("Enter the note");
                String note = sc.nextLine();

                String[] parts = date.split("-");
                int year = Integer.parseInt(parts[0]);
                int month = Integer.parseInt(parts[1]);

                ArrayList<Expenses> list = em.getAllExpenses();
                int id = 1;
                for (Expenses exp : list) {
                    if (exp.getId() >= id) {
                        id = exp.getId() + 1;
                    }
                }

                Expenses e = new Expenses();
                e.setId(id);
                e.setAmount(amount);
                e.setCategory(category);
                e.setDate(date);
                e.setNote(note);
                e.setMonth(month);
                e.setYear(year);

                em.addExpense(e);

                System.out.println("Expense Added!");

            } else if (menu == 2) {

                view.itemList(em.getAllExpenses());

            } else if (menu == 3) {

                System.out.println("Enter ID to delete:");
                int id = sc.nextInt();
                em.delete(id);

            } else if (menu == 4) {

                System.out.println("Search by:");
                System.out.println("1.By Year");
                System.out.println("2.By Month");
                System.out.println("3.By Category");

                int smenu = sc.nextInt();
                sc.nextLine();

                if (smenu == 1) {
                    System.out.println("Enter the Year:");
                    int year = sc.nextInt();
                    view.itemList(em.searchByYear(year));

                } else if (smenu == 2) {
                    System.out.println("Enter the Month:");
                    int month = sc.nextInt();
                    view.itemList(em.searchByMonth(month));

                } else if (smenu == 3) {
                    System.out.println("Enter the Category:");
                    String category = sc.nextLine();
                    view.itemList(em.searchByCategory(category));
                }

            } else if (menu == 5) {

                view.showTotal();

            } else {
                System.out.println("Exiting...");
                break;
            }
        }
    }
}

class ViewScreen {

    ExpensesManager em = new ExpensesManager();

    public void showTotal() {
        System.out.println("Total Expenses : " + em.getTotal());
    }

    public void itemList(ArrayList<Expenses> expense) {

        if (expense.isEmpty()) {
            System.out.println("No data found.");
            return;
        }

        System.out.printf("%-5s %-10s %-15s %-12s %-20s\n",
                "ID", "Amount", "Category", "Date", "Note");
        System.out.println("---------------------------------------------------------------");

        for (Expenses e : expense) {
            System.out.printf("%-5d %-10.2f %-15s %-12s %-20s\n",
                    e.getId(),
                    e.getAmount(),
                    e.getCategory(),
                    e.getDate(),
                    e.getNote());
        }
    }
}

class ExpensesManager {

    private ExpensesDatabase ed = new ExpensesDatabase();

    public void addExpense(Expenses e) {
        ed.insertExpense(e);
    }

    public ArrayList<Expenses> getAllExpenses() {
        return ed.getExpenses();
    }

    public ArrayList<Expenses> searchByYear(int year) {
        return ed.filterByYear(ed.getExpenses(), year);
    }

    public ArrayList<Expenses> searchByMonth(int month) {
        return ed.filterByMonth(ed.getExpenses(), month);
    }

    public ArrayList<Expenses> searchByCategory(String category) {
        return ed.filterByCategory(ed.getExpenses(), category);
    }

    public double getTotal() {
        return ed.calTotal(ed.getExpenses());
    }

    public void delete(int id) {
        ed.deleteExpenses(id);
    }
}

class ExpensesDatabase {

    public double calTotal(ArrayList<Expenses> expense) {
        double total = 0;
        for (Expenses e : expense) {
            total += e.getAmount();
        }
        return total;
    }

    public ArrayList<Expenses> filterByYear(ArrayList<Expenses> expense, int year) {
        ArrayList<Expenses> result = new ArrayList<>();
        for (Expenses e : expense) {
            if (e.getYear() == year)
                result.add(e);
        }
        return result;
    }

    public ArrayList<Expenses> filterByMonth(ArrayList<Expenses> expense, int month) {
        ArrayList<Expenses> result = new ArrayList<>();
        for (Expenses e : expense) {
            if (e.getMonth() == month)
                result.add(e);
        }
        return result;
    }

    public ArrayList<Expenses> filterByCategory(ArrayList<Expenses> expense, String category) {
        ArrayList<Expenses> result = new ArrayList<>();
        for (Expenses e : expense) {
            if (e.getCategory().equalsIgnoreCase(category)) {
                result.add(e);
            }
        }
        return result;
    }

    public void insertExpense(Expenses e) {
        try {
            FileWriter fw = new FileWriter("Expensesdb.csv", true);

            fw.write("\n" +
                    e.getId() + "," +
                    e.getAmount() + "," +
                    e.getCategory() + "," +
                    e.getDate() + "," +
                    e.getNote() + "," +
                    e.getMonth() + "," +
                    e.getYear() + "\n");

            fw.close();

        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    public void deleteExpenses(int id) {
        try {
            BufferedReader br = new BufferedReader(new FileReader("Expensesdb.csv"));
            ArrayList<String> lines = new ArrayList<>();
            String line;

            while ((line = br.readLine()) != null) {
                String[] data = line.split(",");
                if (Integer.parseInt(data[0]) != id) {
                    lines.add(line);
                }
            }
            br.close();

            FileWriter fw = new FileWriter("Expensesdb.csv");
            for (String l : lines) {
                fw.write(l + "\n");
            }
            fw.close();

            System.out.println("Deleted successfully!");

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public ArrayList<Expenses> getExpenses() {
        ArrayList<Expenses> list = new ArrayList<>();

        try {
            BufferedReader br = new BufferedReader(new FileReader("Expensesdb.csv"));
            String line;

            while ((line = br.readLine()) != null) {
                String[] d = line.split(",");
                if (d.length < 7)
                    continue;

                Expenses e = new Expenses();
                e.setId(Integer.parseInt(d[0]));
                e.setAmount(Double.parseDouble(d[1]));
                e.setCategory(d[2]);
                e.setDate(d[3]);
                e.setNote(d[4]);
                e.setMonth(Integer.parseInt(d[5]));
                e.setYear(Integer.parseInt(d[6]));

                list.add(e);
            }

            br.close();

        } catch (Exception e) {
            e.printStackTrace();
        }

        return list;
    }
}

class Expenses {

    private int id;
    private double amount;
    private String category;
    private String date;
    private String note;
    private int month;
    private int year;

    public int getId() { return id; }
    public void setId(int id) { this.id = id; }
    public double getAmount() { return amount; }
    public void setAmount(double amount) { this.amount = amount; }
    public String getCategory() { return category; }
    public void setCategory(String category) { this.category = category; }
    public String getDate() { return date; }
    public void setDate(String date) { this.date = date; }
    public String getNote() { return note; }
    public void setNote(String note) { this.note = note; }
    public int getMonth() { return month; }
    public void setMonth(int month) { this.month = month; }
    public int getYear() { return year; }
    public void setYear(int year) { this.year = year; }
}

003

Cafe Ordering System

A console cafe simulation with a browsable menu, multi-item orders via a running cart, automatic bill calculation, and a printed receipt — fully localized in Japanese.

Java OOP HashMap Console

⚙️ Key Features

Browsable menu of 10 items, each with a name, price, star rating, and description
Separate list view and detail view for individual menu items
Multi-item ordering with quantities tracked in a HashMap keyed by item number
A balance check that blocks checkout if the customer can't cover the total
A printed receipt breaking down each item, quantity, and subtotal

📚 What I Learned

Modeling real-world roles (Customer, Waiter, Menu, Bill) as separate classes
Using a HashMap to track order quantities keyed by menu item number
Validating a purchase against available balance before charging

PracofCafe.java

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Scanner;

public class PracofCafe {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        Customer c = new Customer();
        Waiter w = new Waiter();

        System.out.println("━━━☕ Caffeine Lab ☕━━━");

        w.sayGreet();
        int members = c.tellMembers();
        w.confirmMembers(members);

        CafeDatabase db = new CafeDatabase();
        ArrayList<Menu> menu = db.getMenu();

        w.giveMenu(menu);

        CafeView view = new CafeView();

        while (true) {
            System.out.println("\n1️⃣ 一覧  2️⃣ 詳細  3️⃣ 注文へ");
            System.out.print("👉 選択: ");
            int choice = sc.nextInt();

            if (choice == 1) {
                view.showList(menu);
            } else if (choice == 2) {
                System.out.print("👉 商品番号: ");
                int no = sc.nextInt();
                if (no > 0 && no <= menu.size()) {
                    view.showDetails(menu.get(no - 1));
                }
            } else if (choice == 3) {
                break;
            } else {
                System.out.println("❌ 無効な選択");
            }
        }

        w.takeOrder();
        HashMap<Integer, Integer> orders = c.sayOrder(menu);

        int total = w.confirmOrder(orders, menu);

        if (c.getMoney() < total) {
            System.out.println("❌ お金が足りません！");
            return;
        }

        Bill b = new Bill();
        b.showBill(orders, menu, total);

        c.askBill();
        c.paybill(total);

        w.sayThanks();
    }
}

class Bill {

    public void showBill(HashMap<Integer, Integer> orders, ArrayList<Menu> menu, int total) {

        System.out.println("\n━━━━━━━━━━━━━━━━━━━━");
        System.out.println("🧾 レシート");
        System.out.println("━━━━━━━━━━━━━━━━━━━━");

        for (int key : orders.keySet()) {
            Menu m = menu.get(key - 1);
            int qty = orders.get(key);

            System.out.println("🍽️ " + m.getName() + " × " + qty + " = " + (m.getPrice() * qty) + "円");
        }

        System.out.println("━━━━━━━━━━━━━━━━━━━━");
        System.out.println("💰 合計: " + total + "円");
        System.out.println("━━━━━━━━━━━━━━━━━━━━");
    }
}

class CafeDatabase {

    public ArrayList<Menu> getMenu() {

        ArrayList<Menu> menu = new ArrayList<>();

        menu.add(new Menu("Cappuccino", 450, 4.5, "Espresso with milk foam"));
        menu.add(new Menu("Latte", 500, 4.6, "Smooth coffee with milk"));
        menu.add(new Menu("Espresso", 350, 4.3, "Strong black coffee"));
        menu.add(new Menu("Mocha", 550, 4.7, "Chocolate coffee"));
        menu.add(new Menu("Iced Coffee", 400, 4.2, "Cold coffee"));
        menu.add(new Menu("Cheesecake", 600, 4.8, "Creamy cake"));
        menu.add(new Menu("Chocolate Cake", 580, 4.7, "Rich chocolate"));
        menu.add(new Menu("Croissant", 300, 4.1, "Buttery pastry"));
        menu.add(new Menu("Sandwich", 500, 4.3, "Fresh sandwich"));
        menu.add(new Menu("Pancakes", 650, 4.6, "Soft pancakes"));

        return menu;
    }
}

class CafeView {

    public void showList(ArrayList<Menu> menu) {

        for (int i = 0; i < menu.size(); i++) {
            Menu m = menu.get(i);

            System.out.println("━━━━━━━━━━━━━━━━━━━━");
            System.out.println("🍽️ No." + (i + 1));
            System.out.println("📌 " + m.getName());
            System.out.println("💰 " + m.getPrice() + "円");
        }
    }

    public void showDetails(Menu m) {

        System.out.println("━━━━━━━━━━━━━━━━━━━━");
        System.out.println("🍽️ " + m.getName());
        System.out.println("💰 " + m.getPrice() + "円");

        System.out.print("⭐ " + m.getRating() + " ");
        for (int i = 0; i < (int) m.getRating(); i++) {
            System.out.print("★");
        }
        System.out.println();

        System.out.println("📝 " + m.getDetail());
        System.out.println("━━━━━━━━━━━━━━━━━━━━");
    }
}

class Menu {
    private String name;
    private int price;
    private double rating;
    private String detail;

    public Menu(String name, int price, double rating, String detail) {
        this.name = name;
        this.price = price;
        this.rating = rating;
        this.detail = detail;
    }

    public String getName() { return name; }
    public int getPrice() { return price; }
    public double getRating() { return rating; }
    public String getDetail() { return detail; }
}

class Customer {

    private int money = 2000;
    Scanner sc = new Scanner(System.in);

    public int getMoney() {
        return money;
    }

    public int tellMembers() {
        System.out.print("👉 何名様ですか？: ");
        return sc.nextInt();
    }

    public HashMap<Integer, Integer> sayOrder(ArrayList<Menu> menu) {

        HashMap<Integer, Integer> orders = new HashMap<>();

        while (true) {
            System.out.println("\n1️⃣ 注文する  2️⃣ 終了");
            System.out.print("👉 選択: ");
            int choice = sc.nextInt();

            if (choice == 1) {
                System.out.print("👉 商品番号: ");
                int item = sc.nextInt();

                if (item < 1 || item > menu.size()) {
                    System.out.println("❌ 無効");
                    continue;
                }

                System.out.print("👉 数量: ");
                int qty = sc.nextInt();

                orders.put(item, orders.getOrDefault(item, 0) + qty);
                System.out.println("✅ 追加しました！");

            } else if (choice == 2) {
                break;
            }
        }
        return orders;
    }

    public void askBill() {
        System.out.println("🧑‍💼 お会計お願いします。");
    }

    public void paybill(int total) {
        System.out.println("💳 支払い中...");
        money -= total;
        System.out.println("💸 残高: " + money + "円");
    }
}

class Waiter {

    public void sayGreet() {
        System.out.println("👨‍🍳 いらっしゃいませ！");
    }

    public void confirmMembers(int members) {
        System.out.println("👨‍🍳 " + members + "名様ですね。お席へご案内します。");
    }

    public void giveMenu(ArrayList<Menu> menu) {
        System.out.println("📖 メニューになります。");
    }

    public void takeOrder() {
        System.out.println("👨‍🍳 ご注文をお伺いします。");
    }

    public int confirmOrder(HashMap<Integer, Integer> orders, ArrayList<Menu> menu) {

        int total = 0;

        System.out.println("\n━━━━━━━━━━━━━━━━━━━━");
        System.out.println("✅ ご注文確認");

        for (int key : orders.keySet()) {
            Menu m = menu.get(key - 1);
            int qty = orders.get(key);

            System.out.println("🍽️ 「" + m.getName() + "」× " + qty);
            total += m.getPrice() * qty;
        }

        System.out.println("━━━━━━━━━━━━━━━━━━━━");
        return total;
    }

    public void sayThanks() {
        System.out.println("🙏 ありがとうございました！またお越しください！");
    }
}

004

Student Management System

A console app for managing student records — add new students, list everyone on file, or search by name or country — with all data persisted to a CSV file between sessions.

Java File I/O ArrayList

⚙️ Key Features

Add a student with student number, name, age, and country
List every registered student
Search students by a partial, case-insensitive match on name or country
Data persists across runs via a CSV file (Students.csv)

📚 What I Learned

Separating concerns into Screen (view), StudentDatabase (persistence), and Student (model)
Appending to and reading from a CSV file with try-with-resources
Handling a missing data file gracefully on first run

School.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.ArrayList;
import java.util.Scanner;

public class School {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        StudentDatabase sd = new StudentDatabase();
        Screen view = new Screen();

        while (true) {
            System.out.println("\n1. Student List  2. Student Details  3. Add Student  0. End");
            int menu = sc.nextInt();
            sc.nextLine();

            if (menu == 1) {
                ArrayList<Student> students = sd.getStudents();
                view.displayList(students);

            } else if (menu == 2) {
                ArrayList<Student> students = sd.getStudents();
                System.out.println("Enter Name or Country:");
                String word = sc.nextLine();
                view.displayDetails(students, word);

            } else if (menu == 3) {

                Student s = new Student();
                System.out.println("Enter the Student NO:");
                String studentNo = sc.nextLine();

                System.out.println("Enter the name:");
                String name = sc.nextLine();

                System.out.println("Enter the age:");
                int age = sc.nextInt();
                sc.nextLine();

                System.out.println("Enter the country:");
                String country = sc.nextLine();

                s.setStudentNo(studentNo);
                s.setName(name);
                s.setAge(age);
                s.setCountry(country);

                sd.insertData(s);

                System.out.println("✅ Student Added Successfully!");

            } else if (menu == 0) {
                System.out.println("Exiting...");
                break;

            } else {
                System.out.println("❌ Invalid Choice");
            }
        }

    }
}

class Screen {

    public void displayDetails(ArrayList<Student> students, String word) {
        boolean found = false;

        for (Student s : students) {
            if (s.getName().toLowerCase().contains(word.toLowerCase())
                    || s.getCountry().toLowerCase().contains(word.toLowerCase())) {

                System.out.println("[StudentNO] " + s.getStudentNo());
                System.out.println("[Name] " + s.getName());
                System.out.println("[Age] " + s.getAge());
                System.out.println("[Country] " + s.getCountry());
                System.out.println("--------------------------");

                found = true;
            }
        }

        if (!found) {
            System.out.println("No matching student found.");
        }
    }

    public void displayList(ArrayList<Student> students) {
        if (students.isEmpty()) {
            System.out.println("No students found.");
            return;
        }

        for (Student s : students) {
            System.out.println("[StudentNO] " + s.getStudentNo());
            System.out.println("[Name] " + s.getName());
            System.out.println("---------------------");
        }
    }
}

class StudentDatabase {

    public void insertData(Student s) {
        try (FileWriter fw = new FileWriter("Students.csv", true)) {

            fw.write(s.getStudentNo() + "," +
                    s.getName() + "," +
                    s.getAge() + "," +
                    s.getCountry() + "\n");

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public ArrayList<Student> getStudents() {

        ArrayList<Student> students = new ArrayList<>();

        try (BufferedReader br = new BufferedReader(new FileReader("Students.csv"))) {

            String line;

            while ((line = br.readLine()) != null) {
                String[] arr = line.split(",");

                if (arr.length < 4)
                    continue;

                Student s = new Student();

                s.setStudentNo(arr[0]);
                s.setName(arr[1]);
                s.setAge(Integer.parseInt(arr[2]));
                s.setCountry(arr[3]);

                students.add(s);
            }

        } catch (Exception e) {
            System.out.println("No data file found yet.");
        }

        return students;
    }
}

class Student {

    private String studentNo;
    private String name;
    private int age;
    private String country;

    public String getStudentNo() { return studentNo; }
    public void setStudentNo(String studentNo) { this.studentNo = studentNo; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }
    public String getCountry() { return country; }
    public void setCountry(String country) { this.country = country; }
}

005

Osaka Tourism Website

A multi-page site introducing Osaka's culture, food, and top attractions, complete with a live embedded weather widget and a quick-facts table covering population and highlights.

HTML CSS Weather Widget

⚙️ Key Features

Hero section with a full-width image and overlaid intro text
Sections covering Osaka's culture, access by shinkansen, must-see spots, and basic facts
A live weather widget embedded via external JavaScript
In-page navigation to related pages (food culture, attractions) with hover effects

📚 What I Learned

Structuring a multi-page site with consistent navigation
Layering styled text over a background image with absolute positioning
Embedding a third-party JavaScript widget into a static page

osaka.html (snippet)

<div style="position: relative;">
  <img src="osaka.jpg" width="100%">
  <p style="position:absolute;
    top:20px; left:20px;">
    Osaka is a charming, relaxed city...
  </p>
</div>

View Page

006

Ramen Menu Website

A restaurant-style ramen menu page inspired by Ippudo, featuring hover-animated dish cards with images, prices, and short descriptions for each bowl.

HTML CSS UI Design

⚙️ Key Features

Menu items displayed as image-and-text cards for each ramen dish
Flexbox layout placing dish photos beside name, tagline, and description
A hover animation that lifts each card slightly on mouseover
Ippudo-inspired branding and typography

📚 What I Learned

Building card-based layouts with Flexbox
Using CSS transitions and transform for hover interactions
Combining imagery and typography to evoke a restaurant brand

ramenp.css (snippet)

.menu-item {
  display: flex;
  gap: 20px;
  transition: 0.3s;
}
.menu-item:hover {
  transform: translateY(-5px);
}

View Page

007

Slot Machine Game

A console-based slot machine game where players bet coins and spin random symbols to win rewards.

Java Random Console

⚙️ Key Features

Starts with a 1000-coin balance
Player chooses a bet amount before each spin
Three random animal symbols are generated per spin
Matching all three pays out bet × 100; a non-match subtracts the bet
A short delay between symbol reveals for spin-style pacing

📚 What I Learned

Generating and comparing random values across an array
Using Thread.sleep() to pace output and simulate a spinning reel
Validating bets against the current balance

Test14.java

import java.util.Random;
import java.util.Scanner;

public class Test14 {

    public static void main(String[] args) throws Exception {
        Random r = new Random();
        Scanner sc = new Scanner(System.in);

        System.out.println("ASE GAMBLE！！！！");

        String[] animals = { "😺", "🐶", "🦁", "🐎", };
        int[] result = new int[3];

        int money = 1000;

        while (true) {

            System.out.println("BALANCE : " + money);
            System.out.println("YOU CAN CHOOSE AMOUNT PER SPIN");
            int spin = sc.nextInt();
            if (spin > money) {
                System.out.println("INSUFFICIENT BALANCE");
                System.out.println("DO YOU WANNA CONTINUE. 1.YES  2.NO");
                int ans = sc.nextInt();
                if (ans == 2) {
                    System.out.println("THANK YOU FOR PLAYING");
                    break;
                }
                System.out.println("YOU CAN CHOOSE AMOUNT PER SPIN");
                spin = sc.nextInt();
            }
            for (int i = 0; i < 3; i++) {
                int n = r.nextInt(animals.length);
                new Thread().sleep(1000);
                System.out.print(animals[n]);
                result[i] = n;
            }
            System.out.println();

            if (result[0] == result[1] && result[1] == result[2]) {

                System.out.println("YOU WON");
                money = spin * 100;

            } else {
                System.out.println("TRY AGAIN!!");
                money -= spin;
            }
            System.out.println("DO YOU WANNA CONTINUE. 1.YES  2.NO");
            int ans = sc.nextInt();
            if (ans == 2) {
                System.out.println("THANK YOU FOR PLAYING");
                break;
            }
        }

    }
}

008

Rock-Paper-Scissors Betting Game

A betting game where players compete against the computer and gain or lose coins based on results.

Java Game Logic Random

⚙️ Key Features

Starts with a 1000-yen balance and tracks win/loss counts
Player bets an amount, then picks rock, paper, or scissors
The computer's move is chosen at random
Win pays triple the bet, loss forfeits the bet, draw leaves the balance unchanged
A short 'thinking' animation plays before the result

📚 What I Learned

Implementing full win/lose/draw logic with chained conditionals
Tracking cumulative stats (wins, losses) across a game loop
Adding small delays and emoji to improve the console UX

Test29.java

import java.util.Random;
import java.util.Scanner;

public class Test29 {

    public static void main(String[] args) throws Exception {

        Random r = new Random();
        Scanner sc = new Scanner(System.in);

        System.out.println("✊🖐️✌️ゲーム");

        int money = 1000;
        int win = 0;
        int lose = 0;

        System.out.println("BALANCE:￥" + money);

        while (true) {
            if (money == 0) {
                System.out.println("お金が無くなりました");
                break;
            }

            System.out.println("いっかいいくら賭けますか？");
            int bet = sc.nextInt();

            if (bet > money) {
                System.out.println("お金足りません");
            }

            System.out.println("1:✊グー 2:✌️チョキ 3:🖐️パー");
            int a = sc.nextInt();

            for (int i = 1; i <= 5; i++) {
                System.out.print("🤔");
                new Thread().sleep(500);
            }
            System.out.println();

            int b = r.nextInt(3);

            if (a == 1 && b == 0) {
                System.out.println("DRAW　RESULT あなたは✊グー　PCも✊グー");
            } else if (a == 1 && b == 1) {
                System.out.println("WIN　RESULT あなたは✊グー　PCは✌️チョキ");
                money += bet * 3;
                win++;
            } else if (a == 1 && b == 2) {
                System.out.println("LOSE　RESULT あなたは✊グー　PCも🖐️パー");
                money -= bet;
                lose++;
            } else if (a == 2 && b == 1) {
                System.out.println("DRAW　RESULT あなたは✌️チョキー　PCも✌️チョキー");
            } else if (a == 2 && b == 2) {
                System.out.println("WIN　RESULT あなたは✌️チョキ　PCは🖐️パー");
                money += bet * 3;
                win++;
            } else if (a == 2 && b == 0) {
                System.out.println("LOSE　RESULT あなたは✌️チョキ　PCは✊グー");
                money -= bet;
                lose++;
            } else if (a == 3 && b == 2) {
                System.out.println("DRAW　RESULT あなたは🖐️パー　PCも🖐️パー");
            } else if (a == 3 && b == 0) {
                System.out.println("WIN　RESULT あなたは🖐️パー　PCは✊グー");
                money += bet * 3;
                win++;
            } else if (a == 3 && b == 1) {
                System.out.println("LOSE　RESULT あなたは🖐️パー　PCは✌️チョキー");
                money -= bet;
                lose++;
            }
            System.out.println("お金:￥" + money);

            System.out.println("1:もう一回する 2:終わる");
            int p = sc.nextInt();
            if (p == 2) {
                System.out.println("YOU HAVE ￥" + money);
                System.out.println(win + "回勝ちました");
                System.out.println(lose + "回負けました");
                break;

            }

        }

    }

}

008

ASE Shop

A team-built e-commerce app. The Java backend reads a product catalog from SQLite and generates a live storefront across 12 categories, while an embedded HTTP server handles cart actions, stock validation, and checkout directly in the browser — including delivery date estimates and per-item subtotals.

Java SQLite/JDBC MVC HTTP Server

⚙️ Key Features

Products loaded from a SQLite database and rendered into a browsable HTML storefront across 12 categories
An embedded HTTP server (com.sun.net.httpserver) serves the cart, add/remove/decrease actions, and checkout as live web routes
Cart state is a synchronized list, checked against live stock before an item can be added or purchased
Checkout decrements stock per item, rolls back items that fail, and shows a total plus a randomized delivery date
Star ratings and review counts are generated deterministically per product as sample data

📚 What I Learned

Standing up a lightweight HTTP server in plain Java without a framework
Coordinating shared mutable state (the cart) safely across concurrent requests with synchronized blocks
Separating business logic (CartService) from the web layer (CartServer) so the console app and the browser share the same rules
Working as a team on a shared MVC codebase split across entity, model, view, controller, and web packages

CartService.java

public class CartService {

    private final ProductModel model;
    private final List<CartItem> cart;

    public String addToCart(int productId, int quantity) {
        synchronized (cart) {
            Product product = model.findById(productId);
            if (product == null) {
                return "該当する商品が見つかりませんでした。";
            }

            CartItem existing = findInCart(product.getProductid());
            int alreadyInCart = (existing != null) ? existing.getQuantity() : 0;
            int available = product.getStock() - alreadyInCart;

            if (quantity <= 0 || quantity > available) {
                return "在庫が足りません。追加できる数量: " + available;
            }

            if (existing != null) {
                existing.setQuantity(existing.getQuantity() + quantity);
            } else {
                cart.add(new CartItem(product, quantity));
            }

            return product.getName() + "をカートに追加しました。";
        }
    }

    public CheckoutResult checkout() {
        synchronized (cart) {
            if (cart.isEmpty()) {
                return new CheckoutResult(false, 0, "カートが空です。商品を追加してください。", null);
            }

            List<CartItem> purchased = new ArrayList<CartItem>();
            StringBuilder failures = new StringBuilder();

            for (CartItem item : cart) {
                boolean ok = model.decreaseStock(item.getProduct().getProductid(), item.getQuantity());
                if (ok) {
                    purchased.add(item);
                } else {
                    failures.append(item.getProduct().getName())
                            .append("は在庫不足のため注文できませんでした。カートに残しています。 ");
                }
            }

            int total = 0;
            for (CartItem item : purchased) {
                total += item.getSubtotal();
            }

            cart.removeAll(purchased);

            String message = failures.length() > 0 ? failures.toString().trim() : null;
            return new CheckoutResult(true, total, message, purchased);
        }
    }
}

009

Employee Management System

A console-based employee database app with full CRUD — list, keyword search, ID lookup, add, update, and delete — all backed by a real SQLite database accessed through JDBC with parameterized queries.

Java JDBC SQLite CRUD

⚙️ Key Features

Full CRUD menu: list all, keyword search, ID lookup, add, update, and delete employee records
Every query uses a PreparedStatement with bound parameters, avoiding SQL injection
Keyword search runs a LIKE query so a partial name match still finds the employee
Insert retrieves the auto-generated employee ID back from SQLite after the row is created
Update pre-fills each prompt with the employee's current value so nothing has to be retyped from scratch

📚 What I Learned

Writing parameterized SQL with JDBC instead of concatenating strings
Reading auto-generated keys back from an INSERT with Statement.RETURN_GENERATED_KEYS
Keeping the model layer (SQL) fully separate from the controller (menu flow) and view (console output)

EmployeeModel.java

public class EmployeeModel {

    public ArrayList<Employee> findByKeyword(String word) {

        ArrayList<Employee> employees = new ArrayList<Employee>();

        try {
            Class.forName("org.sqlite.JDBC");
            Connection conn = DriverManager.getConnection("jdbc:sqlite:sample.db");

            String sql = "select * from employees where employeename like ?";
            PreparedStatement stmt = conn.prepareStatement(sql);
            stmt.setString(1, "%" + word + "%");

            ResultSet rs = stmt.executeQuery();
            while (rs.next()) {
                employees.add(mapRow(rs));
            }

            conn.close();

        } catch (Exception e) {
            e.printStackTrace();
        }

        return employees;
    }

    public boolean insert(Employee employee) {

        try {
            Class.forName("org.sqlite.JDBC");
            Connection conn = DriverManager.getConnection("jdbc:sqlite:sample.db");

            String sql = "insert into employees "
                    + "(employeename, height, email, weight, hirefiscalyear, birthday, bloodtype) "
                    + "values (?, ?, ?, ?, ?, ?, ?)";

            PreparedStatement stmt = conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);
            stmt.setString(1, employee.getEmployeeName());
            stmt.setDouble(2, employee.getHeight());
            stmt.setString(3, employee.getMail());
            stmt.setDouble(4, employee.getWeight());
            stmt.setInt(5, employee.getHiredfiscalyear());
            stmt.setString(6, employee.getDOB());
            stmt.setString(7, employee.getBloodType());

            int count = stmt.executeUpdate();

            if (count > 0) {
                ResultSet keys = stmt.getGeneratedKeys();
                if (keys.next()) {
                    employee.setEmployeeId(keys.getInt(1));
                }
            }

            conn.close();
            return count > 0;

        } catch (Exception e) {
            e.printStackTrace();
        }

        return false;
    }
}

010

Robocode AI Combat Bot

An AI-controlled combat robot for the Robocode battle simulator. Duels run on a segmented GuessFactor targeting gun with a hit-rate-based linear-targeting fallback, paired with wave-surfing movement that kinematically simulates its own dodge options in real time. Free-for-all melee rounds switch to separate nearest/weakest-target logic and risk-scored waypoint movement around a home corner.

Java Robocode API AI/Targeting Simulation

⚙️ Key Features

Segmented GuessFactor gun tracking hit outcomes across 9 distance/velocity buckets, with older data decayed each update so the bot keeps adapting if an opponent changes pattern mid-match
A linear-targeting fallback gun chosen per-segment whenever its live hit rate beats the GuessFactor gun's, with hysteresis so a few noisy shots don't flip the aim angle every turn
Wave-surfing movement that kinematically simulates its own forward motion to predict danger from every incoming bullet wave in flight, then orbits in whichever direction scores safer
Melee mode scores targets by distance plus energy to prefer finishing off weak nearby enemies, and roams a risk-scored pocket around a fixed home corner instead of pure potential-field movement
Collision recovery that breaks toward the battlefield center after repeated stalls instead of endlessly retrying the same stuck move

📚 What I Learned

Turning a segmented GuessFactor targeting approach into working Java state kept per distance/velocity bucket
Running a kinematic forward simulation to predict my own future position instead of reacting only to the robot's current state
Designing hysteresis thresholds so a gun or target choice doesn't thrash on noisy, small-sample data
Structuring one robot class to cleanly branch between two very different game modes — 1v1 duels and free-for-all melee

B0347.java

int segment = segmentIndex(enemyDistance, Math.abs(enemyVelocity));

double gfRate = gfShotsFired[segment] < 5
        ? 1.0 : (double) gfHits[segment] / gfShotsFired[segment];
double linearRate = linearShotsFired[segment] < 5
        ? 1.0 : (double) linearHits[segment] / linearShotsFired[segment];

boolean useGf = currentGunIsGf[segment];
if (useGf && linearRate > gfRate + 0.1) {
    useGf = false;
} else if (!useGf && gfRate > linearRate + 0.1) {
    useGf = true;
}
currentGunIsGf[segment] = useGf;

double aimAngle;
if (useGf) {
    int bestIndex = indexOfMaxOrMiddle(gunStats[segment]);
    double guessFactor = (bestIndex - MID) / MID;
    aimAngle = absBearingNow + enemyLatDirection * guessFactor * maxEscapeAngle;
} else {
    aimAngle = linearAimAngle(myX, myY, enemyLocation.x, enemyLocation.y,
            enemyVelocity, enemyHeading, bulletVelocity);
}

012

Things To Do Together

An interactive date-activity planner servlet. Search 23 seeded activities by name, filter by budget tier, select multiple to total up the cost, and add new activities through a form — all rendered as a dynamic HTML page generated on the fly, no database involved.

Java Servlet HTML Forms Filtering

⚙️ Key Features

23 seeded activities (name, budget in yen, category, duration, photo) held in an in-memory list shared across requests
Accent-insensitive search by name, normalizing text like "café" and "cafe" to the same match via Unicode decomposition
Budget filter pills — All / Free / Under ¥1,000 / Under ¥3,000 — combined with the search term through query parameters
Checkbox-select across the filtered list, then "Calculate Total Budget" sums the selected activities' cost
A form posts new activities (name, price, image URL, category, duration) straight into the shared list, visible on the next page load

📚 What I Learned

Building a GET/POST servlet that renders and mutates state through plain query parameters and form fields, with no framework involved
Writing accent-insensitive search with Unicode NFD normalization instead of a naive substring match
Escaping user-supplied values before writing them into generated HTML so form input can't break the markup
Round-tripping filter state (search text, budget tier) through hidden form fields across both the search form and the select/calculate form

Test03Controller.java

private static String normalize(String s) {
    String decomposed = Normalizer.normalize(s, Normalizer.Form.NFD);
    return decomposed.replaceAll("\\p{M}", "").toLowerCase(Locale.ROOT);
}

List<Activity> filtered = new ArrayList<>();
for (Activity a : activities) {
    boolean matchesSearch = q.isEmpty() || normalize(a.name).contains(normalize(q));
    boolean matchesBudget;
    switch (budgetFilter) {
        case "free": matchesBudget = a.budget == 0; break;
        case "under1000": matchesBudget = a.budget < 1000; break;
        case "under3000": matchesBudget = a.budget < 3000; break;
        default: matchesBudget = true;
    }
    if (matchesSearch && matchesBudget) filtered.add(a);
}

013

Omikuji Fortune Draw

An animated Japanese fortune-slip (omikuji) web app rendered entirely from a Java servlet. Click the wooden box to shake and draw one of seven weighted fortune tiers, each revealed through a card-unfold animation, with dark mode and a full reduced-motion fallback for accessibility.

Java Servlet CSS Animation Accessibility

⚙️ Key Features

Seven fortune tiers, from 大吉 (best) down to 大凶 (worst), each with a kanji rank, romaji reading, name, and description, picked by a weighted random roll (best/worst tiers are deliberately rarer)
The whole page — HTML, CSS, and inline JS — is rendered server-side from a single Java text-block template, with the chosen fortune's fields substituted in before the response is written
Click-to-shake animation sequence — box shake, then stick emergence, then fortune card unfold — with an ARIA live region announcing the result for screen readers
Dark mode via prefers-color-scheme, plus a full prefers-reduced-motion fallback that skips straight to the revealed state
"Draw again" reloads the page for a fresh server-side roll rather than re-randomizing on the client

📚 What I Learned

Using Java text blocks to template a full HTML/CSS/JS page server-side with simple string substitution, instead of a view engine
Weighting a random roll across unequal-probability outcomes, since the best and worst fortune tiers are intentionally rarer than the middle ones
Writing CSS keyframe animations that respect prefers-reduced-motion, not just prefers-color-scheme
Wiring an aria-live region so a purely visual reveal animation still announces its result to screen reader users

Test05Controller.java

Random r = new Random();
int num = r.nextInt(100);

String tier, kanji, romaji, name, desc;
if (num < 5) {
    tier = "best"; kanji = "大吉"; romaji = "Daikichi"; name = "最高の運";
    desc = "最高の運勢です。物事はうまくいくでしょう。";
} else if (num < 25) {
    tier = "good"; kanji = "吉"; romaji = "Kichi"; name = "良い運";
    desc = "良いことが起こりそうな、前向きな運勢です。";
} else if (num < 45) {
    tier = "good"; kanji = "中吉"; romaji = "Chūkichi"; name = "なかなか良い運";
    desc = "物事は順調に進みそうですが、少し辛抱が必要かもしれません。";
} // ...small/mid tiers omitted...
} else {
    tier = "worst"; kanji = "大凶"; romaji = "Daikyō"; name = "非常に良くない運";
    desc = "非常に良くない兆しです。断定ではなく、立ち止まって考えるきっかけと捉えましょう。";
}

String html = PAGE_TEMPLATE
        .replace("{{TIER}}", tier)
        .replace("{{KANJI}}", kanji)
        .replace("{{ROMAJI}}", romaji)
        .replace("{{NAME}}", name)
        .replace("{{DESC}}", desc);

Practice & Experiments

Smaller coding-test solutions and one-off exercises — not full projects, but useful snapshots of problem-solving in practice.

Paiza · C166

Coin Change Counter

Breaks a yen amount into the fewest coins possible with a greedy pass over denominations from ¥500 down to ¥1.

C166.java

int[] coins = { 500, 100, 50, 10, 5, 1 };
int count = 0;
for (int coin : coins) {
    count += a / coin;
    a %= coin;
}
System.out.println(count);

Paiza · C183

Board Game Score Simulator

Simulates a sugoroku-style board: a token advances by dice rolls and accumulates each square's score until it runs off the board.

C183.java

int pos = 1;
int total = A[1];
for (int i = 0; i < M; i++) {
    int dice = sc.nextInt();
    pos += dice;
    if (pos > N) break;
    total += A[pos];
}
System.out.println(total);

Paiza · C181

String Length Range Finder

Reads N lines and tracks the running max and min string length, printing the gap between the longest and shortest.

C181.java

int max = 0;
int min = Integer.MAX_VALUE;
for (int i = 0; i < a; i++) {
    String s = sc.nextLine();
    int l = s.length();
    if (l > max) max = l;
    if (l < min) min = l;
}
System.out.println(max - min);

Paiza · C155

Keyword Match Checker

Checks a batch of candidate strings against a target keyword, printing Yes/No for whether each one contains it.

C155.java

String s = sc.nextLine();
int n = Integer.parseInt(sc.nextLine());

for (int i = 0; i < n; i++) {
    String ans = sc.nextLine();
    if (ans.contains(s)) {
        System.out.println("Yes");
    } else {
        System.out.println("No");
    }
}

Paiza · D051

Word Count Validator

Splits a space-separated string into tokens, counts how many equal a target word, and passes/fails against a minimum threshold.

D051.java

String[] ar = str.split(" ");
int count = 0;

for (int i = 0; i < ar.length; i++) {
    if (ar[i].equals("W")) {
        count++;
    }
}
System.out.println(count >= 5 ? "OK" : "NG");

Paiza · D023

Character Counter

Counts how many times a given character appears in a string by scanning it as a char array.

D023.java

char[] ar = s.toCharArray();
int count = 0;

for (int i = 0; i < ar.length; i++) {
    if (ar[i] == 'A') {
        count++;
    }
}
System.out.println(count);

Paiza · C097

FizzBuzz-Style Divisor Classifier

A FizzBuzz-style classifier: loops from 1 to N and prints AB, A, B, or N depending on which of two divisors each number is a multiple of.

C097.java

for (int i = 1; i <= n; i++) {
    if (i % a == 0 && i % b == 0) {
        System.out.println("AB");
    } else if (i % a == 0) {
        System.out.println("A");
    } else if (i % b == 0) {
        System.out.println("B");
    } else {
        System.out.println("N");
    }
}

webapp01 · Test04

Random Greeting Generator

A servlet that renders a random greeting — in Japanese, Burmese, Vietnamese, Sinhala, Hindi, or English — picked fresh on every page load.

Test04Controller.java

Random r = new Random();
int num = r.nextInt(5);

if (num == 0) {
    pw.write("<h1>こんにちは</h1>");
} else if (num == 1) {
    pw.write("<h1>မင်္ဂလာပါ</h1>");
} else if (num == 2) {
    pw.write("<h1>Xin chào</h1>");
} // ...Sinhala, Hindi, and English cases follow the same pattern...

Lesson05 · Myapp02

Kanji Reading Quiz

A multiple-choice quiz testing kanji readings (努力, 労働者, 時間, 季節, 誕生日), tallying a running score as each answer is checked against the correct reading.

Myapp02.java

System.out.println("Q.1 努力");
System.out.println("1.どりょく　2．どうりょく　３．どおりょく");
int ans1 = sci.nextInt();
if (ans1 == 2 || ans1 == 3) {
    System.out.println("WRONG ANSWER");
} else {
    System.out.println("CORRECT");
    score++;
}
// ...remaining questions follow the same check-and-score pattern...

← Back to Main Projects