Java Swing - Creating JTree from a Hashtable and listening to selections

Following is a basic Jtree example. We will create our JTree from Hashtable. We will also add TreeSelectionListener for listening to node selections.

Creating JTree

public class TreeExampleMain {
    public static void main(String[] args) {
        Hashtable<?, ?> projectHierarchy =
                TradingProjectDataService.instance.getProjectHierarchy();
        JTree tree = new JTree(projectHierarchy);
        tree.addTreeSelectionListener(createTreeSelectionListener());
        JFrame frame = createFrame();
        frame.add(new JScrollPane(tree));
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private static TreeSelectionListener createTreeSelectionListener() {
        return treeSelectionEvent -> {
            TreePath path = treeSelectionEvent.getPath();
            System.out.println("Path: " + path);
            Object c = path.getLastPathComponent();
            DefaultMutableTreeNode node = (DefaultMutableTreeNode) c;
            System.out.println("User Object: " + node.getUserObject());
            System.out.println("---");
        };
    }

    private static JFrame createFrame() {
        JFrame frame = new JFrame("JTree basic example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(new Dimension(500, 400));
        return frame;
    }
}

Creating Hashtable

public enum TradingProjectDataService {
    instance;
    private final String ROLES[] =
            {"Project Manager", "Tech Lead", "Developer", "Scrum Master", "Business Analyst"};
    private Hashtable<Object, Object> modules = new Hashtable<>();

    TradingProjectDataService() {
        addModule("Trading", "Real Time Trading", "Order System");
        addModule("Future/Option", "Option Analyzer", "Market Scanning System");
        addModule("Fixed Income", "Bond Tool", "Price/Yield Calculator",
                "Strategy Evaluator");
    }

    private void addModule(String module, String... projects) {
        for (String project : projects) {
            modules.put(module, getProject(module, project));
        }
    }

    private Object getProject(String module, String project) {
        Hashtable<Object, Object> projectMap = new Hashtable<>();
        projectMap.put(project, getEmployeesForProject(module, project));
        return projectMap;
    }

    private Object getEmployeesForProject(String module, String project) {
        //random example employees, in real app we will get it from backend
        String[] employees = new String[ROLES.length];
        for (int i = 0; i < ROLES.length; i++) {
            employees[i] = RandomUtil.getFullName() + " [" + ROLES[i] + "]";
        }
        return employees;
    }

    public Hashtable<?, ?> getProjectHierarchy() {
        return modules;
    }
}

Output

On node selection, following output is printed on the console:

Path: [root, Future/Option, Market Scanning System, Claudie Martindale [Developer]]
User Object: Claudie Martindale [Developer]
---
Path: [root, Future/Option, Market Scanning System, Dorinda Hein [Scrum Master]]
User Object: Dorinda Hein [Scrum Master]
---

Example Project

Dependencies and Technologies Used:

• JDK 1.8
• Maven 3.3.9