The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
When enabling drop on a component, such as a list, you need to decide how you want the drop location to be interpreted.
For example, do you want to restrict the user to replacing existing entries? Do you want to only allow adding or inserting new entries? Do you want to allow both? To configure this behavior, the
JList
class provides the
setDropMode
method which supports the following drop modes.
JList
is DropMode.USE_SELECTION
. When dragging in this mode, the selected item in the list moves to echo the potential drop point. On a drop the selected item shifts to the drop location. This mode is provided for backwards compatibility but is otherwise not recommended.DropMode.ON
, the selected item in the list moves to echo the potential drop point, but the selected item is not affected on the drop. This mode can be used to drop on top of existing list items.DropMode.INSERT
, the user is restricted to selecting the space between existing list items, or before the first item or after the last item in the list. Selecting existing list items is not allowed.DropMode.ON_OR_INSERT
is a combination of the ON
and INSERT
modes.The JTree
class provides the same set of
drop modes and the JTable
class has
several more specific to adding rows or columns.
To obtain the location of the drop, the TransferSupport
class provides the
getDropLocation
method that returns the precise point where the drop has occurred. But for a list component, the index of the drop is more useful than a pixel location, so JList
provides a special subclass, called
JList.DropLocation
. This class provides the
getIndex
and
isInsert
methods, which handle the math for you.
The table, tree, and text components each provide an implementation of DropLocation
with methods that make the most sense for each component. The
JTable.setDropMode
method has the most choices. The following table shows the methods for all four classes:
JList.DropLocation |
JTree.DropLocation |
JTable.DropLocation |
JTextComponent.DropLocation |
---|---|---|---|
isInsert |
getChildIndex |
isInsertRow |
getIndex |
getIndex |
getPath |
isInsertColumn |
getBias |
getRow |
|||
getColumn |
Next is a demo that implements a custom transfer handler for a list component so that it fully participates in drag and drop.