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How to Write a Tree Selection Listener

import javax.swing.JFrame; import javax.swing.JScrollPane; import javax.swing.JTree; import javax.swing.event.TreeSelectionEvent; import javax.swing.event.TreeSelectionListener; import javax.swing.tree.DefaultMutableTreeNode; import javax.swing.tree.TreeSelectionModel; public class UsingTreeSelectionListener {   public static void main(String[] a) {     JFrame frame = new JFrame();     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);     JTree tree = new JTree();     tree.getSelectionModel().setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION);     tree.addTreeSelectionListener(new SelectionListener());     frame.add(new JScrollPane(tree));     frame.setSize(300, 200);     frame.setVisible(true);   } } class SelectionListener implements TreeSelectionListener {   public void valueChanged(TreeSelectionEvent se) {     JTree tree = (JTree) se.getSource();     DefaultMutableTreeNode selectedNode = (DefaultMutableTreeNode) tree         .getLastSelectedPathComponent();     String selectedNodeName = selectedNode.toString();     if (selectedNode.isLeaf()) {       System.out.println(selectedNodeName);     }   } }