QR Code Encoder/Decoder

A QR code encoder and decoder built from scratch in Java without external libraries.

Features

• Encode text strings into QR codes
• Decode QR codes back to text
• Multiple encoding modes:
  • Numeric (0-9)
  • Alphanumeric (A-Z, 0-9, and special characters)
  • Byte (UTF-8 text)
  • Kanji (planned)
• Configurable error correction levels:
  • L - Low (~7% recovery)
  • M - Medium (~15% recovery)
  • Q - Quartile (~25% recovery)
  • H - High (~30% recovery)

Requirements

• Java 17 or higher
• Maven 3.x

Build

mvn clean install

Run

mvn exec:java

The interactive CLI will prompt you to:

1. Choose between encoding or decoding
2. Enter the input string
3. Select an error correction level (for encoding)

Project Structure

src/main/java/com/
├── qr/
│   ├── QR.java           # Main entry point
│   └── utils/
│       └── QRUtils.java  # Encoding/decoding utilities
└── constants/
    ├── Constants.java    # Alphanumeric character set
    ├── ErrorCorrection.java  # Error correction levels enum
    └── Modes.java        # Encoding modes enum

Usage Example

QR Code Encoder/Decoder
Enter 'encode' to encode a string or 'decode' to decode a QR code:
encode
Enter the string to encode:
HELLO WORLD
Choose the error correction level (L, M, Q, H):
M
Encoded QR Code: Encoded(HELLO WORLD)

License

MIT