Module java.desktop
Package javax.swing.event

# Interface TreeWillExpandListener

All Superinterfaces:
  `EventListener`

public interface TreeWillExpandListener extends EventListener
The listener that's notified when a tree expands or collapses a node. For further information and examples see How to Write a Tree-Will-Expand Listener, a section in The Java Tutorial.

## Method Summary

Modifier and Type
Method
Description
`void`
`treeWillCollapse(TreeExpansionEvent event)`
Invoked whenever a node in the tree is about to be collapsed.
`void`
`treeWillExpand(TreeExpansionEvent event)`
Invoked whenever a node in the tree is about to be expanded.

## Method Details

### treeWillExpand

void treeWillExpand(TreeExpansionEvent event) throws ExpandVetoException
Invoked whenever a node in the tree is about to be expanded.

Parameters:
  `event` - a `TreeExpansionEvent` containing a `TreePath` object for the node
Throws:
  `ExpandVetoException` - to signify expansion has been canceled

### treeWillCollapse

void treeWillCollapse(TreeExpansionEvent event) throws ExpandVetoException
Invoked whenever a node in the tree is about to be collapsed.

Parameters:
  `event` - a `TreeExpansionEvent` containing a `TreePath` object for the node
Throws:
  `ExpandVetoException` - to signify collapse has been canceled