Java Swing, 2nd Edition

Rearranging Trees

The JTree class is a ripe candidate for the DnD system. Adding nodes to a tree, moving nodes from one tree to another, or even just rearranging the nodes within a single tree can all be accomplished quite easily with DnD gestures. Unfortunately, JTree does not have any built-in support for these actions. The next few examples take a look at extending JTree to include such features.

A TransferHandler Example

At the beginning of the chapter we mentioned that 1.4 made several parts of the DnD API obsolete—at least for simple tasks. That point is worth reiterating. If you have a simple drop target or a simple drag source that requires custom handling, you can use the TransferHandler class and the transferHandler property of JComponent to do most of your work.

One common feature of graphical trees is the ability to add nodes by dropping them into an existing tree. While the TransferHandler approach cannot handle all of the intricacies of adding and rearranging trees, it can make basic imports very straightforward.

Here’s an example of a tree that can accept incoming lists of files from the native windowing system. You can drag icons from your desktop or file manager and drop them into the tree. They are appended to the root folder.

/* * FSTree.java * A sample component for dragging & dropping a collection of files * into a tree. */ import javax.swing.*; import javax.swing.tree.*; import java.awt.dnd.*; import java.awt.datatransfer.*; import java.util.List; import java.util.Iterator; ...