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ATM System – Wiki Documentation

Welcome to the ATM System Wiki.
This project is a Java-based ATM application with a Swing GUI that simulates banking operations such as balance inquiry, withdrawal, deposit, and loan calculation.

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📌 Table of Contents

• Overview
• System Structure
• User Interface
• PIN Authentication
• ATM Functions
• Loan Calculator
• Input Validation
• Receipt Generation
• Key Concepts
• Execution Flow
• Advantages

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Overview

• Language: Java
• Framework: Swing (GUI)
• Type: Desktop Application

This system demonstrates essential banking features in a secure and modular manner.

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System Structure

Main Class

public class ATMS extends javax.swing.JFrame

• Extends JFrame to create the main application window.

• Handles GUI initialization and event-driven logic.

Core Variables

private double currentBalance = 1000.0;
private int pinAttempts = 0;
private static final int MAX_PIN_ATTEMPTS = 3;

• currentBalance → tracks account balance.

• pinAttempts → tracks failed PIN entries.

• MAX_PIN_ATTEMPTS → maximum retry attempts allowed.

User Interface

The GUI layout is divided into panels:

• Panel 1: Balance & Withdraw controls.

• Panel 2: Central display (PIN entry, status).

• Panel 4: Numeric keypad.

• Panel 5: Loan calculator.

• Panel 6: Loan & Deposit controls.

Example button creation:

jbtnBalance = new javax.swing.JButton();
jbtn1 = new javax.swing.JButton();

Each button is mapped to an event handler.

PIN Authentication

private void jbtnEnterActionPerformed(java.awt.event.ActionEvent evt) {
    int pin = Integer.parseInt(jlblDisplay.getText());
    if (pin == 1234) {
        jbtnBalance.setEnabled(true);
        jlblPinStatus.setText("Access Granted");
    } else {
        pinAttempts++;
        if (pinAttempts >= MAX_PIN_ATTEMPTS) {
            disableAllButtons();
        }
    }
}

• Compares input against stored PIN.

• Locks application after 3 failed attempts.

ATM Functions

Balance Inquiry

private void jbtnBalanceActionPerformed(java.awt.event.ActionEvent evt) {
    jlblDisplay.setText("£" + String.format("%.2f", currentBalance));
}
Displays account balance formatted with 2 decimal places.

Withdrawal
java
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private void jbtnWithdrawActionPerformed(java.awt.event.ActionEvent evt) {
    String input = JOptionPane.showInputDialog(this, "Enter amount to withdraw:");
    double amount = Double.parseDouble(input);
    
    if (amount <= currentBalance) {
        currentBalance -= amount;
    } else {
        JOptionPane.showMessageDialog(this, "Insufficient funds");
    }
}

Checks available funds before allowing withdrawal.

Deposit

(Similar implementation, adds value to balance instead of subtracting.)

Loan Calculator

Interest Rate Assignment

private void updateInterestRate() {
    double loanAmount = Double.parseDouble(jtxtEnteloanamount.getText());
    double interestRate;
    
    if (loanAmount >= 100000) {
        interestRate = 6.0;
    } else if (loanAmount >= 20000) {
        interestRate = 5.5;
    } else {
        interestRate = 5.0;
    }
    
    jtxtInterestRate.setText(String.format("%.1f%%", interestRate));
}

Applies rate based on loan amount:

• ≥ £100,000 → 6%

• £20,000–£99,999 → 5.5%

• < £20,000 → 5%

Loan Payment Formula

double monthlyPayment = loanAmount * monthlyInterestRate / 
    (1 - Math.pow(1 + monthlyInterestRate, -totalMonths));

Standard amortization formula to compute monthly payments.

Input Validation

private void jtxtEnteloanamountKeyTyped(java.awt.event.KeyEvent evt) {
    char character = evt.getKeyChar();
    if (!(Character.isDigit(character) || character == '.' || character == KeyEvent.VK_BACK_SPACE)) {
        evt.consume();
    }
}

Ensures only numeric input (0–9), decimal points, and backspace are allowed.

Receipt Generation

jtxtReceipt.append("\t\tLoan Management System\n");
jtxtReceipt.append("Reference:\t\t\t" + refs + "\n");
jtxtReceipt.append("Amount of Loan:\t\t\t£" + loanAmount + "\n");

Generates a structured receipt containing:

• System header

• Reference number

• Loan amount

• Date and time

Key Concepts

• Event-Driven Programming → Each button triggers a specific action.

• Object-Oriented Design → Components encapsulated as objects.

• Exception Handling → Prevents runtime crashes due to invalid inputs.

• Data Validation → Ensures input consistency.

Execution Flow

• Application initializes GUI.

• User enters PIN → authentication occurs.

• ATM operations enabled (Balance, Withdraw, Deposit, Loan).

• Loan calculator evaluates interest and repayment.

• System generates receipts.

Advantages

Modular: Each feature encapsulated in separate methods.

Secure: PIN authentication with retry limits.

Professional Output: Financial formatting and receipts.

Extendable: Future enhancements (e.g., database connectivity).