Java Programming Projects for Beginners to Build Portfolio

import java.util.HashMap;
import java.util.Map;

class InsufficientFundsException extends Exception {
    InsufficientFundsException(String msg) { super(msg); }
}

class Account {
    private final String id;
    private double balance;
    Account(String id) { this.id = id; }
    void deposit(double amt) { if (amt > 0) balance += amt; }
    void withdraw(double amt) throws InsufficientFundsException {
        if (amt > balance) throw new InsufficientFundsException("Not enough balance in " + id);
        balance -= amt;
    }
    double getBalance() { return balance; }
}

public class Bank {
    private final Map<String, Account> accounts = new HashMap<>();

    void open(String id) { accounts.putIfAbsent(id, new Account(id)); }

    void transfer(String from, String to, double amt) throws InsufficientFundsException {
        accounts.get(from).withdraw(amt);
        accounts.get(to).deposit(amt);
    }

    public static void main(String[] args) {
        Bank bank = new Bank();
        bank.open("A1"); bank.open("B1");
        bank.accounts.get("A1").deposit(500);
        try {
            bank.transfer("A1", "B1", 700);
        } catch (InsufficientFundsException e) {
            System.out.println("Failed: " + e.getMessage());
        }
    }
}

import java.util.*;

record Student(String name, double avg) {}

public class Rankings {
    public static void main(String[] args) {
        List<Student> list = new ArrayList<>(List.of(
            new Student("Aman", 78.5),
            new Student("Neha", 91.0),
            new Student("Ravi", 84.2)));

        list.sort(Comparator.comparingDouble(Student::avg).reversed());

        int rank = 1;
        for (Student s : list) {
            System.out.printf("%d. %s - %.1f%n", rank++, s.name(), s.avg());
        }
    }
}
// 'record' needs Java 16 or newer

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class ProductDao {
    private final String url = "jdbc:mysql://localhost:3306/inventory";
    private final String user = System.getenv("DB_USER");
    private final String pass = System.getenv("DB_PASS");

    public void add(String name, int qty) throws SQLException {
        String sql = "INSERT INTO products (name, qty) VALUES (?, ?)";
        try (Connection c = DriverManager.getConnection(url, user, pass);
             PreparedStatement ps = c.prepareStatement(sql)) {
            ps.setString(1, name);
            ps.setInt(2, qty);
            ps.executeUpdate();
        }
    }

    public List<String> lowStock(int limit) throws SQLException {
        String sql = "SELECT name FROM products WHERE qty < ? ORDER BY qty";
        List<String> names = new ArrayList<>();
        try (Connection c = DriverManager.getConnection(url, user, pass);
             PreparedStatement ps = c.prepareStatement(sql)) {
            ps.setInt(1, limit);
            try (ResultSet rs = ps.executeQuery()) {
                while (rs.next()) names.add(rs.getString("name"));
            }
        }
        return names;
    }
}

-- MySQL schema for the inventory project
CREATE DATABASE IF NOT EXISTS inventory;
USE inventory;

CREATE TABLE products (
  id    INT AUTO_INCREMENT PRIMARY KEY,
  name  VARCHAR(100) NOT NULL UNIQUE,
  qty   INT NOT NULL DEFAULT 0 CHECK (qty >= 0)
);

INSERT INTO products (name, qty) VALUES
  ('Notebook', 40), ('Pen', 8), ('Stapler', 3);

SELECT name, qty FROM products WHERE qty < 10 ORDER BY qty;

// Task.java
import jakarta.persistence.*;

@Entity
public class Task {
    @Id @GeneratedValue
    private Long id;
    private String title;
    private boolean done;

    public Long getId() { return id; }
    public String getTitle() { return title; }
    public void setTitle(String title) { this.title = title; }
    public boolean isDone() { return done; }
    public void setDone(boolean done) { this.done = done; }
}

// TaskRepository.java
import org.springframework.data.jpa.repository.JpaRepository;

public interface TaskRepository extends JpaRepository<Task, Long> {}

import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import java.util.List;

@RestController
@RequestMapping("/tasks")
public class TaskController {
    private final TaskRepository repo;
    public TaskController(TaskRepository repo) { this.repo = repo; }

    @GetMapping
    public List<Task> all() { return repo.findAll(); }

    @PostMapping
    public ResponseEntity<Task> create(@RequestBody Task task) {
        if (task.getTitle() == null || task.getTitle().isBlank()) {
            return ResponseEntity.badRequest().build();
        }
        return ResponseEntity.status(201).body(repo.save(task));
    }

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> delete(@PathVariable Long id) {
        if (!repo.existsById(id)) return ResponseEntity.notFound().build();
        repo.deleteById(id);
        return ResponseEntity.noContent().build();
    }
}

# Inventory Manager (Java + JDBC + MySQL)

A console app to track products and stock levels.

## Features
- Add, update and remove products
- Low-stock report
- Input validation and custom exceptions

## Tech
Java 17, JDBC, MySQL, JUnit 5, Maven

## Run
1. Create the database using schema.sql
2. Set DB_USER and DB_PASS environment variables
3. mvn package && java -jar target/inventory.jar

## Design
- DAO pattern separates SQL from business logic
- PreparedStatement used for all queries

## What I learned

inventory-manager/
  README.md
  pom.xml
  schema.sql
  src/main/java/com/example/inventory/
      App.java
      model/Product.java
      dao/ProductDao.java
      service/InventoryService.java
  src/test/java/com/example/inventory/
      InventoryServiceTest.java
  .gitignore

90-second project pitch

1. What: "An inventory manager for a small shop"
2. Why: "To practise JDBC and clean layering"
3. How: "DAO layer, service layer, console UI"
4. Challenge: "Preventing negative stock; solved with a
   CHECK constraint and validation in the service"
5. Proof: "Tests cover add, remove and low stock"
6. Next: "Turn it into a Spring Boot REST API"