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.
The tree-will-expand listener prevents a tree node from expanding or collapsing. To be notified just after an expansion or collapse occurs, you should use a tree expansion listener instead.
This demo adds a tree-will-expand listener to the TreeExpandEventDemo
example discussed in How to Write a Tree Expansion Listener. The code added here demonstrates that tree-will-expand listeners prevent node expansions and collapses: The listener will prompt you for confirmation each time you try to expand a node.
treeWillCollapse
method lets the collapse occur, uncontested.The following snippet shows the code that this program adds to TreeExpandEventDemo
. The bold line prevents the tree expansion from happening. You can find all the demo's source code in
TreeExpandEventDemo2.java
.
public class TreeExpandEventDemo2 ... { ... class DemoArea ... implements ... TreeWillExpandListener { ... public DemoArea() { ... tree.addTreeWillExpandListener(this); ... } ... //Required by TreeWillExpandListener interface. public void treeWillExpand(TreeExpansionEvent e) throws ExpandVetoException { saySomething("Tree-will-expand event detected", e); //...show a dialog... if (/* user said to cancel the expansion */) { //Cancel expansion. saySomething("Tree expansion cancelled", e); throw new ExpandVetoException(e); } } //Required by TreeWillExpandListener interface. public void treeWillCollapse(TreeExpansionEvent e) { saySomething("Tree-will-collapse event detected", e); } ... } }
The TreeWillExpandListener Interface
TreeWillExpandListener
has no adapter class.
Method | Purpose |
---|---|
treeWillCollapse(TreeExpansionEvent) | Called just before a tree node collapses. To prevent the collapse from occurring, your implementation of this method should throw a
ExpandVetoException event. |
treeWillExpand(TreeExpansionEvent) | Called just before a tree node expands. To prevent the expansion from occurring, your implementation of this method should throw a
ExpandVetoException event. |
See The Tree Expansion Event API for information about the
TreeExpansionEvent
argument for the preceding methods.
TreeExpandEventDemo2
, featured in this section, is our only example that uses a tree-will-expand listener.