Java Foundation Classes in a Nutshell

CHAPTER 12

Thejava.awt.dnd Package

The java.awt.dnd package contains classes and interfaces that support data transfer

thr ough the drag-and-drop metaphor; the package is new in Java 1.2. This

functionality is built upon the data transfer framework of the java.awt.datatransfer

package.

A DragSource object is a proxy for an object that initiates a drag, while a DropTarget

object is a proxy for an object that wishes to accept drops. All inter-object commu-

nication during the drag process is done through the various event classes defined

by this package. Figure 12-1 shows the class hierarchy of this package. See Chap-

ter 6, Data Transfer, for more details on drag-and-drop.

Autoscroll Ja va 1.2

java.awt.dnd

This interface allows a scrollable component to scroll itself as part of the drag-and-drop

pr ocess, so that a user can drop an object anywhere within the component’s scrollable

content. Consider, for example, the problem of cutting a paragraph of text from the top

of a long document and dragging it down to the bottom of the same document. While

the drag-and-drop operation is in progr ess, the user obviously cannot operate the

scr ollbar, since the mouse is already in use. So some other technique is necessary to

enable scrolling during a drag-and-drop operation.

The Autoscroll inter face enables this specialized form of scr olling. When an object is first

dragged over a component that implements