TreeWillExpandListener (Java SE 11 & JDK 11 )
Keywords: javax.swing.event.TreeWillExpandListener interface

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

    All Methods Instance Methods Abstract Methods
    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 Detail

    - #### 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