Module java.desktop

# Package java.awt.dnd

package java.awt.dnd
Drag and Drop is a direct manipulation gesture found in many Graphical User Interface systems that provides a mechanism to transfer information between two entities logically associated with presentation elements in the GUI. Normally driven by a physical gesture of a human user using an appropriate input device, Drag and Drop provides both a mechanism to enable continuous feedback regarding the possible outcome of any subsequent data transfer to the user during navigation over the presentation elements in the GUI, and the facilities to provide for any subsequent data negotiation and transfer.

This package defines the classes and interfaces necessary to perform Drag and Drop operations in Java. It defines classes for the drag-source and the drop-target, as well as events for transferring the data being dragged. This package also provides a means for giving visual feedback to the user throughout the duration of the Drag and Drop operation.

A typical Drag and Drop operation can be decomposed into the following states (not entirely sequentially):

- A `DragSource` comes into existence, associated with some presentation element (`Component`) in the GUI, to initiate a Drag and Drop of some potentially `Transferable` data.
- 1 or more `DropTarget`(s) come into/go out of existence, associated with presentation elements in the GUI (Components), potentially capable of consuming `Transferable` data types.
- A `DragGestureRecognizer` is obtained from the `DragSource` and is associated with a `Component` in order to track and identify any Drag initiating gesture by the user over the `Component`.
- A user makes a Drag gesture over the `Component`, which the registered `DragGestureRecognizer` detects, and notifies its `DragGestureListener` of.

  Note: Although this API consistently refers to the stimulus for a drag and drop operation being a physical gesture by a human user, this does not preclude a programmatically driven DnD operation given the appropriate implementation of a `DragSource`. This package contains the abstract class `MouseDragGestureRecognizer` for recognizing mouse device gestures. Other abstract subclasses may be provided by the platform to support other input devices or particular `Component` class semantics.

- The `DragGestureListener` causes the `DragSource` to initiate the Drag and Drop operation on behalf of the user, perhaps animating the GUI Cursor and/or rendering an `Image` of the item(s) that are the subject of the operation.
- As the user gestures navigate over `Component`(s) in the GUI with associated `DropTarget`(s), the `DragSource` receives notifications in order to provide "Drag Over" feedback effects, and the `DropTarget`(s) receive notifications in order to provide "Drag Under" feedback effects based upon the operation(s) supported and the data type(s) involved.

The gesture itself moves a logical cursor across the GUI hierarchy, intersecting the geometry of GUI Component(s), possibly resulting in the logical "Drag" cursor entering, crossing, and subsequently leaving `Component`(s) and associated `DropTarget`(s).

The `DragSource` object manifests "Drag Over" feedback to the user, in the typical case by animating the GUI `Cursor` associated with the logical cursor.

`DropTarget` objects manifest "Drag Under" feedback to the user, in the typical case, by rendering animations into their associated GUI `Component`(s) under the GUI Cursor.

The determination of the feedback effects, and the ultimate success or failure of the data transfer, should one occur, is parameterized as follows:

- By the transfer "operation" selected by the user, and supported by both the `DragSource` and `DropTarget`: Copy, Move or Reference(link).
- By the intersection of the set of data types provided by the `DragSource` and the set of data types comprehensible by the `DropTarget`.
- When the user terminates the drag operation, normally resulting in a successful Drop, both the `DragSource` and `DropTarget` receive notifications that include, and result in the type negotiation and transfer of, the information associated with the `DragSource` via a `Transferable` object.

Since:
  1.2

- Related Packages
  Package
  Description
  java.awt
  Contains all of the classes for creating user interfaces and for painting graphics and images.
- Class
  Description
  Autoscroll
  During DnD operations it is possible that a user may wish to drop the subject of the operation on a region of a scrollable GUI control that is not currently visible to the user.
  DnDConstants
  This class contains constant values representing the type of action(s) to be performed by a Drag and Drop operation.
  DragGestureEvent
  A `DragGestureEvent` is passed to `DragGestureListener`'s dragGestureRecognized() method when a particular `DragGestureRecognizer` detects that a platform dependent drag initiating gesture has occurred on the `Component` that it is tracking.
  DragGestureListener
  The listener interface for receiving drag gesture events.
  DragGestureRecognizer
  The `DragGestureRecognizer` is an abstract base class for the specification of a platform-dependent listener that can be associated with a particular `Component` in order to identify platform-dependent drag initiating gestures.
  DragSource
  The `DragSource` is the entity responsible for the initiation of the Drag and Drop operation, and may be used in a number of scenarios: 1 default instance per JVM for the lifetime of that JVM.
  DragSourceAdapter
  An abstract adapter class for receiving drag source events.
  DragSourceContext
  The `DragSourceContext` class is responsible for managing the initiator side of the Drag and Drop protocol.
  DragSourceDragEvent
  The `DragSourceDragEvent` is delivered from the `DragSourceContextPeer`, via the `DragSourceContext`, to the `DragSourceListener` registered with that `DragSourceContext` and with its associated `DragSource`.
  DragSourceDropEvent
  The `DragSourceDropEvent` is delivered from the `DragSourceContextPeer`, via the `DragSourceContext`, to the `dragDropEnd` method of `DragSourceListener`s registered with that `DragSourceContext` and with its associated `DragSource`.
  DragSourceEvent
  This class is the base class for `DragSourceDragEvent` and `DragSourceDropEvent`.
  DragSourceListener
  The `DragSourceListener` defines the event interface for originators of Drag and Drop operations to track the state of the user's gesture, and to provide appropriate "drag over" feedback to the user throughout the Drag and Drop operation.
  DragSourceMotionListener
  A listener interface for receiving mouse motion events during a drag operation.
  DropTarget
  The `DropTarget` is associated with a `Component` when that `Component` wishes to accept drops during Drag and Drop operations.
  DropTarget.DropTargetAutoScroller
  this protected nested class implements autoscrolling
  DropTargetAdapter
  An abstract adapter class for receiving drop target events.
  DropTargetContext
  A `DropTargetContext` is created whenever the logical cursor associated with a Drag and Drop operation coincides with the visible geometry of a `Component` associated with a `DropTarget`.
  DropTargetDragEvent
  The `DropTargetDragEvent` is delivered to a `DropTargetListener` via its dragEnter() and dragOver() methods.
  DropTargetDropEvent
  The `DropTargetDropEvent` is delivered via the `DropTargetListener` drop() method.
  DropTargetEvent
  The `DropTargetEvent` is the base class for both the `DropTargetDragEvent` and the `DropTargetDropEvent`.
  DropTargetListener
  The `DropTargetListener` interface is the callback interface used by the `DropTarget` class to provide notification of DnD operations that involve the subject `DropTarget`.
  InvalidDnDOperationException
  This exception is thrown by various methods in the java.awt.dnd package.
  MouseDragGestureRecognizer
  This abstract subclass of `DragGestureRecognizer` defines a `DragGestureRecognizer` for mouse-based gestures.