TreeWillExpandListener (Java SE 11 & JDK 11 )

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