I read this and thought "I've never used a JTree before, I wonder how
hard that might be"

...

import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.SwingUtilities;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreePath;

public class TreeTest extends JPanel {

    JTree tree;

    TreeTest() {
        Person ceo = new Person("Steve Gates", "123-456-789");
        DefaultMutableTreeNode root = new DefaultMutableTreeNode(ceo);

        Person fd = new Person("Bill Jobs", "013-453-263");
        DefaultMutableTreeNode child1 = new DefaultMutableTreeNode(fd);
        root.add(child1);

        Person hrd = new Person("Darl Torvalds", "987-765-324");
        DefaultMutableTreeNode child2 = new DefaultMutableTreeNode(hrd);
        root.add(child2);

        final JTree tree = new JTree(root);
        add(new JScrollPane(tree));

        MouseListener ml = new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                int selRow = tree.getRowForLocation(e.getX(), e.getY());
                TreePath selPath = tree.getPathForLocation(
                        e.getX(), e.getY());
                DefaultMutableTreeNode node =
                        (DefaultMutableTreeNode)
                         selPath.getLastPathComponent();
                Person x = (Person)node.getUserObject();
                if (selRow != -1) {
                    if (e.getClickCount() == 2) {
                        JOptionPane.showMessageDialog(
                                null, x.allAboutMe());
                    }
                }
            }
        };
        tree.addMouseListener(ml);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JFrame f = new JFrame("Tree Test");
                f.add(new TreeTest());
                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                f.pack();
                f.setVisible(true);
            }
        });
    }
}

class Person {
    String name;

    String ssn;

    Person(String name, String ssn) {
        this.name = name;
        this.ssn = ssn;
    }

    public String allAboutMe() {
        return "Name: " + name + ", SSN: " + ssn;
    }

    public String toString() {
        return name;
    }
}

Doubtless the above can be improved enormously. I just quickly cut &
pasted the examples in the Javadocs and looked for suitable methods to
get objects out. If I was to use a JTree for real I'd try to use
generics to get rid of the type casts and maybe look for other types of
listeners that could be used (node selected?)