Cajero Automático

Console-based ATM simulator with authentication, balance inquiry, withdrawals, deposits, and transfers. Academic project for the Diseño de Interfaces course.

Stack

Layer	Technology
Language	Java 26
Database	SQLite (JDBC)
Auth	PIN hashing with SHA-256 + salt
IDE	IntelliJ IDEA

Requirements

• JDK >= 26
• sqlite-jdbc driver JAR in classpath

Setup & Running

# 1. Clone the repository
git clone <repo-url>
cd cajero

# 2. Compile
javac -cp ".:path/to/sqlite-jdbc.jar" -d out src/**/*.java

# 3. Run
java -cp "out:path/to/sqlite-jdbc.jar" Main

Or open the project folder in IntelliJ IDEA — add sqlite-jdbc.jar to the project dependencies and run Main.java.

The database file banco.db is created automatically in the working directory on first run.

Seed Credentials

Field	Value
User ID	111111111
Name	Juan Perez
PIN	1234
Account Number	999999999
Initial Balance	5,420 CUP

Project Structure

src/
├── Main.java                 # Entry point
├── dao/
│   ├── DatabaseManager.java  # SQLite connection & schema init
│   ├── UsuarioDAO.java       # Users CRUD
│   ├── CuentaDAO.java        # Accounts CRUD
│   └── TransaccionDAO.java   # Transactions CRUD
├── model/
│   ├── Usuario.java          # User entity
│   ├── Cuenta.java           # Account entity
│   └── Transaccion.java      # Transaction entity (enum Tipo)
├── service/
│   ├── AuthService.java      # Login, PIN validation
│   ├── CuentaService.java    # Balance, history
│   └── TransaccionService.java # Withdraw, deposit, transfer
├── ui/
│   └── Menu.java             # Console UI (menus, prompts)
└── util/
    ├── Formatter.java        # Currency & date formatting
    ├── InputHelper.java      # User input (Scanner + Console)
    └── PinHasher.java        # SHA-256 PIN hashing

Layered Architecture

Main
  └── Menu (UI)
        └── Services (business logic)
              └── DAOs (data access)
                    └── DatabaseManager (SQLite)

• model/ — Plain entities (Usuario, Cuenta, Transaccion)
• dao/ — Data access layer with raw SQL via JDBC
• service/ — Business logic orchestration
• ui/ — Console interface (Menu)
• util/ — Helpers (hashing, formatting, input)

Features

Feature	Description
Login	Authenticate with numeric ID + 4-digit PIN (3 attempts max)
Balance Inquiry	Display current balance in CUP
Withdrawal	Predefined amounts (5–2,000 CUP) or custom amount
Deposit	Add funds to the account
Transfer	Send money to another account with atomic commit/rollback
Transaction History	Last 10 movements with type, amount (+/-), and date

Business Rules

• Login attempts: after 3 failed PIN attempts, the session is blocked (program restarts).
• PIN security: PINs are hashed with SHA-256 + salt (CAJERO_APP_2025_). Never stored in plain text.
• Positive amounts: withdrawals, deposits, and transfers require a positive amount.
• Sufficient balance: transfers and withdrawals check that the source account has enough funds.
• Transfer atomicity: transfers use SQL transactions (setAutoCommit(false) + commit/rollback) — both debit and credit execute or neither does.
• Target validation: the destination account must exist; the recipient's name is shown for confirmation before executing.
• History scope: only the last 10 transactions for the authenticated account are shown.

Database Schema

CREATE TABLE usuarios (
    id TEXT PRIMARY KEY,
    nombre TEXT NOT NULL,
    pin_hash TEXT NOT NULL,
    created_at TEXT DEFAULT CURRENT_TIMESTAMP
);

CREATE TABLE cuentas (
    numero TEXT PRIMARY KEY,
    usuario_id TEXT NOT NULL,
    saldo REAL DEFAULT 0.0,
    created_at TEXT DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (usuario_id) REFERENCES usuarios(id)
);

CREATE TABLE transacciones (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    cuenta_origen TEXT NOT NULL,
    tipo TEXT NOT NULL CHECK(tipo IN ('RETIRO','DEPOSITO','TRANSFERENCIA')),
    monto REAL NOT NULL,
    cuenta_destino TEXT,
    descripcion TEXT,
    fecha TEXT DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (cuenta_origen) REFERENCES cuentas(numero)
);