Overview

This project is a compact Java Swing paint application that demonstrates interactive GUI programming, basic drawing, and event handling in Java. The program provides a simple canvas where the user can draw freehand by dragging the mouse, choose between preset colors, and clear the drawing. It is implemented in a single source file (PaintApp.java) to keep the example focused and easy to study.

The primary goals are:

• provide a minimal, runnable example of custom painting with Swing/AWT
• illustrate handling mouse events and drawing to an off-screen image
• show a straightforward way to structure a small GUI app for learning and experimentation

Demo video: Software Demo Video

Features

• Freehand drawing with the mouse (click-and-drag)
• Three color choices: Black, Red, Blue
• Clear canvas button to reset the drawing
• Uses an off-screen image to preserve drawing between repaints

Additional implemented features:

• Undo: remove the last stroke
• Export PNG: export the current canvas as a .png image
• Load PNG as background: open a PNG and use it as the drawing background (clears strokes)
• Internal design: strokes are stored as nested ArrayList<List<LineSegment>> (demonstrates Java Collections)
• Demonstrates abstract inheritance (ShapeStorage) and a simple storage implementation

How to Run

Make sure you have a Java JDK installed (Java SE 8 or later recommended). From the project directory run:

javac PaintApp.java
java PaintApp

The application opens a window with a small toolbar on top and a white drawing canvas.

Save / Export / Load usage:

• Export as PNG image: Click Save → choose a filename (the app will append .png if you omit an extension). The saved PNG contains the current canvas and strokes.
• Load a PNG: Click Load → open a .png file to use as the canvas background (this clears any existing strokes).

Development Environment

• Language: Java (Swing / AWT)
• Minimum: JDK 8; tested with JDK 11+
• Build tools: javac and java (no external build system required)
• Recommended IDEs: IntelliJ IDEA, Eclipse, or VS Code with the Java extension pack

The app uses only standard Java libraries (no external dependencies). All UI and drawing code is contained within PaintApp.java.

Useful Websites

• Oracle Java Tutorials — Swing: https://docs.oracle.com/javase/tutorial/uiswing/
• Oracle Java SE Documentation: https://docs.oracle.com/en/java/
• ZetCode Swing Tutorial (concise examples): https://zetcode.com/java/
• Stack Overflow — for troubleshooting specific API usage questions

Project Structure

• PaintApp.java — main application and GUI implementation

Future Work

Ideas and improvements to make this program more feature-complete:

• Add more colors and a color picker dialog
• Add brush size selection and custom stroke styles
• Add simple shape tools (lines, rectangles, ovals)
• Improve layout and accessibility of the UI

Remaining / suggested next steps:

• Add a dedicated "Export PNG" button to make exporting explicit and simpler for users (the Save dialog supports PNG already).
• Add brush-size UI and keyboard shortcuts for better UX.
• Implement a full undo/redo stack (currently Undo removes only the last stroke).
• Create a runnable JAR and native installers using jpackage for easy distribution to non-technical users.
• Replace Java object serialization for project files with a human-readable format (JSON) if desired.