Swing uses TransferHandlers to implement drag and drop. Write a custom TransferHandler and attach it to the JComponent you want to be dnd-enabled.

However, there are a few catches you should be aware of:

• A JComponent you want to be dnd-enabled needs to be on top of everything else to receive clicks. Usually this isn't a problem, but whenever you use a CellRenderer, or other flyweight, it can become an issue.
• A JComponent that has both a TransferHandler and a MouseMotionListener attached will never run the MouseMotionListener code. This is apparently a bug Swing acknowledges with the Windows implementation of dnd, but they have no plans to fix it.
• Drag and Drop is only enabled by default for certain JComponents: List of DnD enabled JComponents

General Information

Purpose: Swing TransferHandlers are intended to make Drag and Drop operations easier to implement by using the Swing framework.

Javadoc Link: http://download.oracle.com/javase/6/docs/api/javax/swing/TransferHandler.html

Swing Drag and Drop Tutorial: http://download.oracle.com/javase/tutorial/uiswing/dnd/intro.html

Overview of TransferHandlers used in SE II

We've implemented several subclasses of TransferHandler to deal with the drag and drop needs of our interface:

• SETreeTransferHandler deals with the dragging and dropping of rows into and out of the main tree.
• BindingTransferHandler deals with the dragging and dropping of bindings between binding slots within tree rows.
• BindingTransferHandlerExportOnly deals with beginning a drag operation from the Custom picker for pinball.
• DefaultPickerTransferHandlerExportOnly deals with beginning a drag operation from the default game object picker.
• LibraryTransferHandler deals with importing of tree rows into the Library pane (promoting them to patterns) and exporting them into Stories.
• StartItTransferHandler deals with dragging and dropping of Causes onto an Encounter.

How to Write TransferHandlers

1. Create a new class and make it extend TransferHandler.
2. Override any of the linked methods to change the drag and drop behaviour: method list

Special Considerations

The Windows implementation of Swing drag and drop conflicts horribly with several MouseMotionListener methods. If you have a TransferHandler registered on a JComponent, and you try to add a MouseMotionListener (say because you want to draw a transparent ghost of the JComponent alongside the mouse pointer as it's dragged, or something else equally reasonable and sane), the MouseMotionListener methods will never fire because the event is consumed by the drag and drop implementation. Also, you can't modify the Swing drag and drop implementation because everything is private and references private classes, so we're stuck misusing the mouseClicked method to begin a drag and drop operation. Thanks, Swing!