DragSource (Java SE 17 & JDK 17)
Description: declaration: module: java.desktop, package: java.awt.dnd, class: DragSource
Keywords: java.awt.dnd.DragSource class

Module java.desktop
Package java.awt.dnd

# Class DragSource

java.lang.Object
java.awt.dnd.DragSource

All Implemented Interfaces:
  `Serializable`

public class DragSource extends Object implements Serializable
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.
- 1 instance per class of potential Drag Initiator object (e.g TextField). [implementation dependent]
- 1 per instance of a particular `Component`, or application specific object associated with a `Component` instance in the GUI. [implementation dependent]
- Some other arbitrary association. [implementation dependent]

Once the `DragSource` is obtained, a `DragGestureRecognizer` should also be obtained to associate the `DragSource` with a particular `Component`.

The initial interpretation of the user's gesture, and the subsequent starting of the drag operation are the responsibility of the implementing `Component`, which is usually implemented by a `DragGestureRecognizer`.

When a drag gesture occurs, the `DragSource`'s startDrag() method shall be invoked in order to cause processing of the user's navigational gestures and delivery of Drag and Drop protocol notifications. A `DragSource` shall only permit a single Drag and Drop operation to be current at any one time, and shall reject any further startDrag() requests by throwing an `IllegalDnDOperationException` until such time as the extant operation is complete.

The startDrag() method invokes the createDragSourceContext() method to instantiate an appropriate `DragSourceContext` and associate the `DragSourceContextPeer` with that.

If the Drag and Drop System is unable to initiate a drag operation for some reason, the startDrag() method throws a `java.awt.dnd.InvalidDnDOperationException` to signal such a condition. Typically this exception is thrown when the underlying platform system is either not in a state to initiate a drag, or the parameters specified are invalid.

Note that during the drag, the set of operations exposed by the source at the start of the drag operation may not change until the operation is complete. The operation(s) are constant for the duration of the operation with respect to the `DragSource`.

Since:
  1.2
See Also:
  - Serialized Form

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final Cursor`
  `DefaultCopyDrop`
  The default `Cursor` to use with a copy operation indicating that a drop is currently allowed.
  `static final Cursor`
  `DefaultCopyNoDrop`
  The default `Cursor` to use with a copy operation indicating that a drop is currently not allowed.
  `static final Cursor`
  `DefaultLinkDrop`
  The default `Cursor` to use with a link operation indicating that a drop is currently allowed.
  `static final Cursor`
  `DefaultLinkNoDrop`
  The default `Cursor` to use with a link operation indicating that a drop is currently not allowed.
  `static final Cursor`
  `DefaultMoveDrop`
  The default `Cursor` to use with a move operation indicating that a drop is currently allowed.
  `static final Cursor`
  `DefaultMoveNoDrop`
  The default `Cursor` to use with a move operation indicating that a drop is currently not allowed.

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `DragSource()`
  Creates a new `DragSource`.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `addDragSourceListener(DragSourceListener dsl)`
  Adds the specified `DragSourceListener` to this `DragSource` to receive drag source events during drag operations initiated with this `DragSource`.
  `void`
  `addDragSourceMotionListener(DragSourceMotionListener dsml)`
  Adds the specified `DragSourceMotionListener` to this `DragSource` to receive drag motion events during drag operations initiated with this `DragSource`.
  `DragGestureRecognizer`
  `createDefaultDragGestureRecognizer(Component c, int actions, DragGestureListener dgl)`
  Creates a new `DragGestureRecognizer` that implements the default abstract subclass of `DragGestureRecognizer` for this `DragSource`, and sets the specified `Component` and `DragGestureListener` on the newly created object.
  `<T extends DragGestureRecognizer>
  T`
  `createDragGestureRecognizer(Class<T> recognizerAbstractClass, Component c, int actions, DragGestureListener dgl)`
  Creates a new `DragGestureRecognizer` that implements the specified abstract subclass of `DragGestureRecognizer`, and sets the specified `Component` and `DragGestureListener` on the newly created object.
  `protected DragSourceContext`
  `createDragSourceContext(DragGestureEvent dgl, Cursor dragCursor, Image dragImage, Point imageOffset, Transferable t, DragSourceListener dsl)`
  Creates the `DragSourceContext` to handle the current drag operation.
  `static DragSource`
  `getDefaultDragSource()`
  Gets the `DragSource` object associated with the underlying platform.
  `DragSourceListener[]`
  `getDragSourceListeners()`
  Gets all the `DragSourceListener`s registered with this `DragSource`.
  `DragSourceMotionListener[]`
  `getDragSourceMotionListeners()`
  Gets all of the `DragSourceMotionListener`s registered with this `DragSource`.
  `static int`
  `getDragThreshold()`
  Returns the drag gesture motion threshold.
  `FlavorMap`
  `getFlavorMap()`
  This method returns the `FlavorMap` for this `DragSource`.
  `<T extends EventListener>
  T[]`
  `getListeners(Class<T> listenerType)`
  Gets all the objects currently registered as `FooListener`s upon this `DragSource`.
  `static boolean`
  `isDragImageSupported()`
  Reports whether or not drag `Image` support is available on the underlying platform.
  `void`
  `removeDragSourceListener(DragSourceListener dsl)`
  Removes the specified `DragSourceListener` from this `DragSource`.
  `void`
  `removeDragSourceMotionListener(DragSourceMotionListener dsml)`
  Removes the specified `DragSourceMotionListener` from this `DragSource`.
  `void`
  `startDrag(DragGestureEvent trigger, Cursor dragCursor, Transferable transferable, DragSourceListener dsl)`
  Start a drag, given the `DragGestureEvent` that initiated the drag, the initial `Cursor` to use, the `Transferable` subject data of the drag, and the `DragSourceListener`.
  `void`
  `startDrag(DragGestureEvent trigger, Cursor dragCursor, Transferable transferable, DragSourceListener dsl, FlavorMap flavorMap)`
  Start a drag, given the `DragGestureEvent` that initiated the drag, the initial `Cursor` to use, the `Transferable` subject data of the drag, the `DragSourceListener`, and the `FlavorMap`.
  `void`
  `startDrag(DragGestureEvent trigger, Cursor dragCursor, Image dragImage, Point dragOffset, Transferable transferable, DragSourceListener dsl)`
  Start a drag, given the `DragGestureEvent` that initiated the drag, the initial `Cursor` to use, the `Image` to drag, the offset of the `Image` origin from the hotspot of the `Cursor` at the instant of the trigger, the subject data of the drag, and the `DragSourceListener`.
  `void`
  `startDrag(DragGestureEvent trigger, Cursor dragCursor, Image dragImage, Point imageOffset, Transferable transferable, DragSourceListener dsl, FlavorMap flavorMap)`
  Start a drag, given the `DragGestureEvent` that initiated the drag, the initial `Cursor` to use, the `Image` to drag, the offset of the `Image` origin from the hotspot of the `Cursor` at the instant of the trigger, the `Transferable` subject data of the drag, the `DragSourceListener`, and the `FlavorMap`.

  ### Methods declared in class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Field Details

  - ### DefaultCopyDrop

    public static final Cursor DefaultCopyDrop
    The default `Cursor` to use with a copy operation indicating that a drop is currently allowed. `null` if `GraphicsEnvironment.isHeadless()` returns `true`.
    See Also:
      - `GraphicsEnvironment.isHeadless()`

  - ### DefaultMoveDrop

    public static final Cursor DefaultMoveDrop
    The default `Cursor` to use with a move operation indicating that a drop is currently allowed. `null` if `GraphicsEnvironment.isHeadless()` returns `true`.
    See Also:
      - `GraphicsEnvironment.isHeadless()`

  - ### DefaultLinkDrop

    public static final Cursor DefaultLinkDrop
    The default `Cursor` to use with a link operation indicating that a drop is currently allowed. `null` if `GraphicsEnvironment.isHeadless()` returns `true`.
    See Also:
      - `GraphicsEnvironment.isHeadless()`

  - ### DefaultCopyNoDrop

    public static final Cursor DefaultCopyNoDrop
    The default `Cursor` to use with a copy operation indicating that a drop is currently not allowed. `null` if `GraphicsEnvironment.isHeadless()` returns `true`.
    See Also:
      - `GraphicsEnvironment.isHeadless()`

  - ### DefaultMoveNoDrop

    public static final Cursor DefaultMoveNoDrop
    The default `Cursor` to use with a move operation indicating that a drop is currently not allowed. `null` if `GraphicsEnvironment.isHeadless()` returns `true`.
    See Also:
      - `GraphicsEnvironment.isHeadless()`

  - ### DefaultLinkNoDrop

    public static final Cursor DefaultLinkNoDrop
    The default `Cursor` to use with a link operation indicating that a drop is currently not allowed. `null` if `GraphicsEnvironment.isHeadless()` returns `true`.
    See Also:
      - `GraphicsEnvironment.isHeadless()`

- ## Constructor Details

  - ### DragSource

    public DragSource() throws HeadlessException
    Creates a new `DragSource`.
    Throws:
      `HeadlessException` - if GraphicsEnvironment.isHeadless() returns true
    See Also:
      - `GraphicsEnvironment.isHeadless()`

- ## Method Details

  - ### getDefaultDragSource

    public static DragSource getDefaultDragSource()
    Gets the `DragSource` object associated with the underlying platform.
    Returns:
      the platform DragSource
    Throws:
      `HeadlessException` - if GraphicsEnvironment.isHeadless() returns true
    See Also:
      - `GraphicsEnvironment.isHeadless()`

  - ### isDragImageSupported

    public static boolean isDragImageSupported()
    Reports whether or not drag `Image` support is available on the underlying platform.
    Returns:
      if the Drag Image support is available on this platform

  - ### startDrag

    public void startDrag(DragGestureEvent trigger, Cursor dragCursor, Image dragImage, Point imageOffset, Transferable transferable, DragSourceListener dsl, FlavorMap flavorMap) throws InvalidDnDOperationException
    Start a drag, given the `DragGestureEvent` that initiated the drag, the initial `Cursor` to use, the `Image` to drag, the offset of the `Image` origin from the hotspot of the `Cursor` at the instant of the trigger, the `Transferable` subject data of the drag, the `DragSourceListener`, and the `FlavorMap`.
    Parameters:
      `trigger` - the `DragGestureEvent` that initiated the drag
      `dragCursor` - the initial `Cursor` for this drag operation or `null` for the default cursor handling; see DragSourceContext for more details on the cursor handling mechanism during drag and drop
      `dragImage` - the image to drag or `null`
      `imageOffset` - the offset of the `Image` origin from the hotspot of the `Cursor` at the instant of the trigger
      `transferable` - the subject data of the drag
      `dsl` - the `DragSourceListener`
      `flavorMap` - the `FlavorMap` to use, or `null`
    Throws:
      `InvalidDnDOperationException` - if the Drag and Drop system is unable to initiate a drag operation, or if the user attempts to start a drag while an existing drag operation is still executing

  - ### startDrag

    public void startDrag(DragGestureEvent trigger, Cursor dragCursor, Transferable transferable, DragSourceListener dsl, FlavorMap flavorMap) throws InvalidDnDOperationException
    Start a drag, given the `DragGestureEvent` that initiated the drag, the initial `Cursor` to use, the `Transferable` subject data of the drag, the `DragSourceListener`, and the `FlavorMap`.
    Parameters:
      `trigger` - the `DragGestureEvent` that initiated the drag
      `dragCursor` - the initial `Cursor` for this drag operation or `null` for the default cursor handling; see DragSourceContext for more details on the cursor handling mechanism during drag and drop
      `transferable` - the subject data of the drag
      `dsl` - the `DragSourceListener`
      `flavorMap` - the `FlavorMap` to use or `null`
    Throws:
      `InvalidDnDOperationException` - if the Drag and Drop system is unable to initiate a drag operation, or if the user attempts to start a drag while an existing drag operation is still executing

  - ### startDrag

    public void startDrag(DragGestureEvent trigger, Cursor dragCursor, Image dragImage, Point dragOffset, Transferable transferable, DragSourceListener dsl) throws InvalidDnDOperationException
    Start a drag, given the `DragGestureEvent` that initiated the drag, the initial `Cursor` to use, the `Image` to drag, the offset of the `Image` origin from the hotspot of the `Cursor` at the instant of the trigger, the subject data of the drag, and the `DragSourceListener`.
    Parameters:
      `trigger` - the `DragGestureEvent` that initiated the drag
      `dragCursor` - the initial `Cursor` for this drag operation or `null` for the default cursor handling; see DragSourceContext for more details on the cursor handling mechanism during drag and drop
      `dragImage` - the `Image` to drag or `null`
      `dragOffset` - the offset of the `Image` origin from the hotspot of the `Cursor` at the instant of the trigger
      `transferable` - the subject data of the drag
      `dsl` - the `DragSourceListener`
    Throws:
      `InvalidDnDOperationException` - if the Drag and Drop system is unable to initiate a drag operation, or if the user attempts to start a drag while an existing drag operation is still executing

  - ### startDrag

    public void startDrag(DragGestureEvent trigger, Cursor dragCursor, Transferable transferable, DragSourceListener dsl) throws InvalidDnDOperationException
    Start a drag, given the `DragGestureEvent` that initiated the drag, the initial `Cursor` to use, the `Transferable` subject data of the drag, and the `DragSourceListener`.
    Parameters:
      `trigger` - the `DragGestureEvent` that initiated the drag
      `dragCursor` - the initial `Cursor` for this drag operation or `null` for the default cursor handling; see DragSourceContext class for more details on the cursor handling mechanism during drag and drop
      `transferable` - the subject data of the drag
      `dsl` - the `DragSourceListener`
    Throws:
      `InvalidDnDOperationException` - if the Drag and Drop system is unable to initiate a drag operation, or if the user attempts to start a drag while an existing drag operation is still executing

  - ### createDragSourceContext

    protected DragSourceContext createDragSourceContext(DragGestureEvent dgl, Cursor dragCursor, Image dragImage, Point imageOffset, Transferable t, DragSourceListener dsl)
    Creates the `DragSourceContext` to handle the current drag operation.

    To incorporate a new `DragSourceContext` subclass, subclass `DragSource` and override this method.

    If `dragImage` is `null`, no image is used to represent the drag over feedback for this drag operation, but `NullPointerException` is not thrown.

    If `dsl` is `null`, no drag source listener is registered with the created `DragSourceContext`, but `NullPointerException` is not thrown.

    Parameters:
      `dgl` - The `DragGestureEvent` that triggered the drag
      `dragCursor` - The initial `Cursor` for this drag operation or `null` for the default cursor handling; see DragSourceContext class for more details on the cursor handling mechanism during drag and drop
      `dragImage` - The `Image` to drag or `null`
      `imageOffset` - The offset of the `Image` origin from the hotspot of the cursor at the instant of the trigger
      `t` - The subject data of the drag
      `dsl` - The `DragSourceListener`
    Returns:
      the `DragSourceContext`
    Throws:
      `NullPointerException` - if `dscp` is `null`
      `NullPointerException` - if `dgl` is `null`
      `NullPointerException` - if `dragImage` is not `null` and `imageOffset` is `null`
      `NullPointerException` - if `t` is `null`
      `IllegalArgumentException` - if the `Component` associated with the trigger event is `null`.
      `IllegalArgumentException` - if the `DragSource` for the trigger event is `null`.
      `IllegalArgumentException` - if the drag action for the trigger event is `DnDConstants.ACTION_NONE`.
      `IllegalArgumentException` - if the source actions for the `DragGestureRecognizer` associated with the trigger event are equal to `DnDConstants.ACTION_NONE`.

  - ### getFlavorMap

    public FlavorMap getFlavorMap()
    This method returns the `FlavorMap` for this `DragSource`.
    Returns:
      the `FlavorMap` for this `DragSource`

  - ### createDragGestureRecognizer

    public <T extends DragGestureRecognizer> T createDragGestureRecognizer(Class<T> recognizerAbstractClass, Component c, int actions, DragGestureListener dgl)
    Creates a new `DragGestureRecognizer` that implements the specified abstract subclass of `DragGestureRecognizer`, and sets the specified `Component` and `DragGestureListener` on the newly created object.
    Type Parameters:
      `T` - the type of `DragGestureRecognizer` to create
    Parameters:
      `recognizerAbstractClass` - the requested abstract type
      `actions` - the permitted source drag actions
      `c` - the `Component` target
      `dgl` - the `DragGestureListener` to notify
    Returns:
      the new `DragGestureRecognizer` or `null` if the `Toolkit.createDragGestureRecognizer` method has no implementation available for the requested `DragGestureRecognizer` subclass and returns `null`

  - ### createDefaultDragGestureRecognizer

    public DragGestureRecognizer createDefaultDragGestureRecognizer(Component c, int actions, DragGestureListener dgl)
    Creates a new `DragGestureRecognizer` that implements the default abstract subclass of `DragGestureRecognizer` for this `DragSource`, and sets the specified `Component` and `DragGestureListener` on the newly created object. For this `DragSource` the default is `MouseDragGestureRecognizer`.
    Parameters:
      `c` - the `Component` target for the recognizer
      `actions` - the permitted source actions
      `dgl` - the `DragGestureListener` to notify
    Returns:
      the new `DragGestureRecognizer` or `null` if the `Toolkit.createDragGestureRecognizer` method has no implementation available for the requested `DragGestureRecognizer` subclass and returns `null`

  - ### addDragSourceListener

    public void addDragSourceListener(DragSourceListener dsl)
    Adds the specified `DragSourceListener` to this `DragSource` to receive drag source events during drag operations initiated with this `DragSource`. If a `null` listener is specified, no action is taken and no exception is thrown.
    Parameters:
      `dsl` - the `DragSourceListener` to add
    Since:
      1.4
    See Also:
      - `removeDragSourceListener(java.awt.dnd.DragSourceListener)`
      - `getDragSourceListeners()`

  - ### removeDragSourceListener

    public void removeDragSourceListener(DragSourceListener dsl)
    Removes the specified `DragSourceListener` from this `DragSource`. If a `null` listener is specified, no action is taken and no exception is thrown. If the listener specified by the argument was not previously added to this `DragSource`, no action is taken and no exception is thrown.
    Parameters:
      `dsl` - the `DragSourceListener` to remove
    Since:
      1.4
    See Also:
      - `addDragSourceListener(java.awt.dnd.DragSourceListener)`
      - `getDragSourceListeners()`

  - ### getDragSourceListeners

    public DragSourceListener[] getDragSourceListeners()
    Gets all the `DragSourceListener`s registered with this `DragSource`.
    Returns:
      all of this `DragSource`'s `DragSourceListener`s or an empty array if no such listeners are currently registered
    Since:
      1.4
    See Also:
      - `addDragSourceListener(java.awt.dnd.DragSourceListener)`
      - `removeDragSourceListener(java.awt.dnd.DragSourceListener)`

  - ### addDragSourceMotionListener

    public void addDragSourceMotionListener(DragSourceMotionListener dsml)
    Adds the specified `DragSourceMotionListener` to this `DragSource` to receive drag motion events during drag operations initiated with this `DragSource`. If a `null` listener is specified, no action is taken and no exception is thrown.
    Parameters:
      `dsml` - the `DragSourceMotionListener` to add
    Since:
      1.4
    See Also:
      - `removeDragSourceMotionListener(java.awt.dnd.DragSourceMotionListener)`
      - `getDragSourceMotionListeners()`

  - ### removeDragSourceMotionListener

    public void removeDragSourceMotionListener(DragSourceMotionListener dsml)
    Removes the specified `DragSourceMotionListener` from this `DragSource`. If a `null` listener is specified, no action is taken and no exception is thrown. If the listener specified by the argument was not previously added to this `DragSource`, no action is taken and no exception is thrown.
    Parameters:
      `dsml` - the `DragSourceMotionListener` to remove
    Since:
      1.4
    See Also:
      - `addDragSourceMotionListener(java.awt.dnd.DragSourceMotionListener)`
      - `getDragSourceMotionListeners()`

  - ### getDragSourceMotionListeners

    public DragSourceMotionListener[] getDragSourceMotionListeners()
    Gets all of the `DragSourceMotionListener`s registered with this `DragSource`.
    Returns:
      all of this `DragSource`'s `DragSourceMotionListener`s or an empty array if no such listeners are currently registered
    Since:
      1.4
    See Also:
      - `addDragSourceMotionListener(java.awt.dnd.DragSourceMotionListener)`
      - `removeDragSourceMotionListener(java.awt.dnd.DragSourceMotionListener)`

  - ### getListeners

    public <T extends EventListener> T[] getListeners(Class<T> listenerType)
    Gets all the objects currently registered as `FooListener`s upon this `DragSource`. `FooListener`s are registered using the `addFooListener` method.
    Type Parameters:
      `T` - the type of listener objects
    Parameters:
      `listenerType` - the type of listeners requested; this parameter should specify an interface that descends from `java.util.EventListener`
    Returns:
      an array of all objects registered as `FooListener`s on this `DragSource`, or an empty array if no such listeners have been added
    Throws:
      `ClassCastException` - if `listenerType` doesn't specify a class or interface that implements `java.util.EventListener`
    Since:
      1.4
    See Also:
      - `getDragSourceListeners()`
      - `getDragSourceMotionListeners()`

  - ### getDragThreshold

    public static int getDragThreshold()
    Returns the drag gesture motion threshold. The drag gesture motion threshold defines the recommended behavior for `MouseDragGestureRecognizer`s.

    If the system property `awt.dnd.drag.threshold` is set to a positive integer, this method returns the value of the system property; otherwise if a pertinent desktop property is available and supported by the implementation of the Java platform, this method returns the value of that property; otherwise this method returns some default value. The pertinent desktop property can be queried using `java.awt.Toolkit.getDesktopProperty("DnD.gestureMotionThreshold")`.

    Returns:
      the drag gesture motion threshold
    Since:
      1.5
    See Also:
      - `MouseDragGestureRecognizer`