ATM Simulation (Cajero Real)

Desktop ATM simulator built with Java Swing — supports withdrawals, deposits, transfers between accounts, transaction history, and PIN changes. Data is persisted in SQLite.

Screenshots

Add screenshots here once you have them. Drop image files into a screenshots/ folder and reference them like:

![Login Screen](screenshots/login.png)
![Menu](screenshots/menu.png)

Stack

• Language: Java 26
• UI: Swing + FlatLaf 3.6 (IntelliJ theme)
• Build: Gradle 9.5 (Kotlin DSL, wrapper included)
• Database: SQLite 3.49 via JDBI 3 3.47 (lightweight SQL mapper)
• Persistence: JDBI BeanMapper — no ORM, no bytecode enhancement

Requirements

• JDK >= 26 (verify with java -version)
• Git (optional, for cloning)

Setup & Running

# 1. Clone or navigate to the project
cd Cajero_Real

# 2. Build and run (Gradle wrapper auto-downloads Gradle)
./gradlew run

On Wayland (e.g., niri, Hyprland, Sway), the window may appear blank. Run with:

_JAVA_AWT_WM_NONREPARENTING=1 ./gradlew run

From IntelliJ: open the Cajero_Real folder, then run CajeroApp.main() or the Gradle application > run task.

For IntelliJ on Wayland, add _JAVA_AWT_WM_NONREPARENTING=1 to the Run Configuration's environment variables.

Seed Cards

Card Number	PIN	Holder	Balance
4821	1234	Carlos Rodriguez	$15,000.00
9734	5678	Maria Garcia	$25,000.00

Both accounts are created automatically on first run. Delete cajero_real.db to reset.

Screens

Login → Menu → Withdraw / Deposit / Transfer / History / Change PIN

Screen	Description
Login	Teal screen, enter 4-digit PIN. 3 attempts before the card is locked.
Menu	Welcome message with balance. Six action buttons.
Withdraw	Preset amounts ($100, $200, $500, $1000) or custom. Confirmation dialog before processing.
Deposit	Enter amount, updates balance immediately.
Transfer	Destination account (16-digit number) and amount. Validates balance.
History	Scrollable log of all operations for the current session.
Change PIN	Enter current PIN, new PIN, confirm. Validates length, digits, and mismatch.

Payment cards are hardcoded as "4821" — the login screen does not ask for a card number. This is a simplified demo.

Architecture

com.cajero
├── CajeroApp.java               Entry point — FlatLaf setup, DB init, launches UI
├── config/
│   └── DatabaseManager.java     JDBI + SQLite connection, table creation, seed data
├── model/
│   ├── Cuenta.java              Account POJO
│   ├── Transaccion.java         Transaction POJO
│   └── TipoTransaccion.java     Enum: WITHDRAW, DEPOSIT, TRANSFER
├── service/
│   ├── AuthService.java         PIN validation, attempt counter
│   ├── CuentaService.java       Account CRUD (JDBI queries)
│   └── TransaccionService.java  Transaction registry + history
├── controller/
│   ├── LoginController.java
│   ├── MenuController.java
│   ├── RetiroController.java
│   ├── DepositoController.java
│   ├── TransferenciaController.java
│   ├── HistorialController.java
│   └── CambioPinController.java
└── ui/
    ├── MainFrame.java           JFrame + CardLayout (7 screens)
    ├── component/
    │   └── PanelAnimator.java   Fade utility (currently instant)
    └── panel/
        ├── LoginPanel.java
        ├── MenuPanel.java
        ├── RetiroPanel.java
        ├── DepositoPanel.java
        ├── TransferenciaPanel.java
        ├── HistorialPanel.java
        └── CambioPinPanel.java

Layers

Layer	Responsibility
Model	Plain Java objects (POJOs) with getters/setters
Service	Business logic + database access via JDBI
Controller	Mediates between panels and services
UI	Swing panels with null layout (absolute positioning)

Business Rules

• Login limit: 3 failed PIN attempts → card blocked → app exits after 3 seconds.
• Withdraw: amount must be positive, must not exceed available balance.
• Transfer: destination must be exactly 16 numeric digits, amount must be positive and not exceed balance.
• Deposit: only validates positivity.
• PIN change: requires current PIN, then new PIN must be 4 digits, numeric, and different from the current one. Both entries must match.
• Persistence: every operation writes to SQLite immediately. Balance updates and transactions are written in the same service call.

Database Schema

CREATE TABLE cuentas (
    id        INTEGER PRIMARY KEY AUTOINCREMENT,
    titular   TEXT    NOT NULL,
    tarjeta   TEXT    NOT NULL UNIQUE,
    pin_hash  TEXT    NOT NULL,
    saldo     REAL    NOT NULL DEFAULT 0.0
);

CREATE TABLE transacciones (
    id              INTEGER PRIMARY KEY AUTOINCREMENT,
    tipo            TEXT    NOT NULL,  -- RETIRO, DEPOSITO, TRANSFERENCIA
    monto           REAL    NOT NULL,
    fecha           TEXT    NOT NULL,  -- ISO-8601
    cuenta_id       INTEGER NOT NULL,
    cuenta_destino  TEXT,
    saldo_posterior REAL    NOT NULL
);

PINs are stored as Integer.toHexString(pin.hashCode()) — simple hashing, not cryptographic. Adequate for a school project.

Scripts

./gradlew build           # Assemble JAR
./gradlew compileJava     # Compile only
./gradlew run             # Build + run
./gradlew clean           # Clean build artifacts (keeps DB)

Troubleshooting

Problem	Solution
Blank/white window on Linux	Your WM is Wayland. See "Setup & Running" for the environment variable fix.
DB corruption or wants fresh data	Delete cajero_real.db and re-run — seed data is inserted automatically.
Port conflicts	None — this is a desktop app, no server ports.
Slow UI or stutter	Run with _JAVA_AWT_WM_NONREPARENTING=1. The alpha compositing animation was removed for Wayland compatibility.

Project Status

All core features are implemented and compile cleanly. The UI uses absolute positioning (null layout) — functional but does not resize. Contributions welcome for:

• Layout migration to GridBagLayout or MigLayout
• Adding a card number input to the login screen
• Withdrawal receipt simulation
• Dark theme toggle
• i18n (Spanish/English)