Building Custom Diagram Editors Using JHotDraw

JFrame frame = new JFrame(“Simple JHotDraw Editor”);Drawing drawing = new DefaultDrawing();DrawingView view = new DefaultDrawingView();view.setDrawing(drawing); // ToolsTool creationTool = new RectangleCreationTool(); // creates RectangleFiguresTool selectionTool = new SelectionTool(); // Editor / ToolbarJToolBar toolbar = new JToolBar();toolbar.add(makeButton(“Select”, selectionTool));toolbar.add(makeButton(“Rectangle”, creationTool)); frame.add(toolbar, BorderLayout.NORTH);frame.add(view.getComponent(), BorderLayout.CENTER);frame.setSize(800,600);frame.setVisible(true);

Note: Use JHotDraw’s built-in Tool implementations (or subclass AbstractTool) and Figure implementations (e.g., RectangleFigure).

Typical workflow when extending JHotDraw

1. Define custom Figure subclasses for domain-specific shapes (override drawing, connectors, and handles).
2. Implement custom Tools if interactions differ (e.g., constrained resizing, snapping).
3. Register Actions for persistence and editing (undo/redo, saving).
4. Wire up copy/paste, keyboard shortcuts, and context menus.
5. Add serialization (XML or JSON) using JHotDraw’s Storable framework or your own I/O.

Tips and best practices

• Follow the MVC separation: keep model (Drawing/Figures) decoupled from view logic.
• Prefer composition over inheritance: reuse existing Figure components and decorate when possible.
• Implement Handles for consistent resizing and transformation behavior.
• Use JHotDraw’s undo/redo support by wrapping state changes in Commands.
• Start with a small set of tools and figures, then iterate.

Debugging and testing

• Log tool events and figure lifecycle methods to trace interaction flow.
• Test saving/loading early to avoid breaking persistence later.
• Use smaller drawings to validate performance before scaling.

Where to go next

• Add connectors and multi-figure alignment features.
• Implement snap-to-grid, zoom, and export to SVG.
• Explore JHotDraw examples and study its source to learn idiomatic patterns.

This guide gives the essential steps to get a basic JHotDraw editor running and the path to extend it into a fuller application.