In the com.mycompany.mavenselectionsuite package, create a new Java class named Event.

Modify the class to declare the following fields and getters:

package com.mycompany.mavenselectionsuite;

import java.util.Date;

public final class Event {

   private final Date date = new Date();
   private static int count = 0;
   private final int index;

   public Event() {
      index = count++;
   }

   public Date getDate() {
      return date;
   }

   public int getIndex() {
      return index;
   }

   public String toString() {
       return index + " - " + date;
   }
}

Right-click the MyAPI project node and choose Properties to open the Properties window.

Select the com.mycompany.mavenselectionsuite package in the Public Packages category:

Figure 5. Public packages selection

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>nbm-maven-plugin</artifactId>
    <extensions>true</extensions>
    <configuration>
        <publicPackages>
            <publicPackage>com.mycompany.mavenselectionsuite</publicPackage>
        </publicPackages>
    </configuration>
</plugin>

Right-click the project and choose Build. When you build the project, the nbm-maven-plugin will generate a manifest header in the MANIFEST.MF of the JAR, to specify the public package:

Manifest-Version: 1.0
OpenIDE-Module-Localizing-Bundle: com/mycompany/mavenselectionsuite/Bu
 ndle.properties
OpenIDE-Module-Specification-Version: 1.0
OpenIDE-Module-Implementation-Version: 1.0-20251013
OpenIDE-Module-Build-Version: 202510130007
OpenIDE-Module: com.mycompany.MyAPI
OpenIDE-Module-Public-Packages: com.mycompany.mavenselectionsuite.*
OpenIDE-Module-Requires: org.openide.modules.ModuleFormat1
OpenIDE-Module-Display-Category: com.mycompany
OpenIDE-Module-Name: MyAPI
OpenIDE-Module-Short-Description: <undefined>
OpenIDE-Module-Long-Description: <undefined>
OpenIDE-Module-Module-Dependencies: org.netbeans.api.annotations.commo
 n/1 > 1.57

Choose File > New Project from the main menu (Ctrl-Shift-N). Select NetBeans Module from the Maven category:

Figure 7. Selecting Netbeans Module as project type

Type MyViewer as the Project Name. Make sure to set the Project Location to the MavenSelectionSuite directory:

Figure 8. New Module parameters 1/2

Click Next. Select the NetBeans API version you’d like to use:

Figure 9. New Module parameters 2/2

The new module is created within the parent project, which is a Maven reactor. Therefore, it becomes part of the reactor build. However, the new module is not yet part of the app project. Right-click the Dependencies node in the app project and choose Add Dependency:

Figure 10. Adding Module to the application

Select the MyViewer module in the Open Projects tab:

Figure 11. Finding new module in Open Projects

When you click Add above, the IDE adds the MyViewer module to the list of dependencies of the app project. You can see the new dependency in the POM of the app project module and displayed as a new node under the Dependencies node of the app project:

Figure 12. Result of adding the dependency

The module is going to use the API module, therefore we need to set a dependency in the viewer module on the API module. Right-click the Dependencies node in the MyViewer project and choose Add Dependency:

Figure 13. Adding MyAPI dependency

Select the MyAPI module in the Open Projects tab:

Figure 14. Finding MyAPI in Open Projects

When you click Add above, the IDE adds the API module to the list of dependencies of the MyViewer module. You can see the new dependency in the POM of the MyViewer module and displayed as a new node under the Dependencies node of the MyViewer module:

Figure 15. Result of adding the dependency

Right-click the MyViewer project and choose New > Window. Select explorer and check Open on Application Start:

Figure 16. New Window creation

Type MyViewer as the Class Name Prefix:

Figure 17. New Window parameters

Figure 18. Window class in source tree

Drag two Labels from the Palette into the window component:

Figure 19. Adding labels to the window

You are now going to listen to the global context, provided by the NetBeans Lookup, for Event objects. Right now, no Event objects will be present in the global context. However, in the next section, we will create a new module that will publish Event objects.

public class MyViewerTopComponent extends TopComponent implements LookupListener {

private Lookup.Result<Event> result = null;

@Override
public void resultChanged(LookupEvent le) {
    if (!result.allInstances().isEmpty()) {
        for (Event event : result.allInstances()) {
            jLabel1.setText(Integer.toString(event.getIndex()));
            jLabel2.setText(event.getDate().toString());
        }
    } else {
        jLabel1.setText("[no selection]");
        jLabel2.setText("");
    }
}

@Override
public void componentOpened() {
    result = Utilities.actionsGlobalContext().lookupResult(Event.class);
    result.addLookupListener(this);
}

@Override
public void componentClosed() {
    result.removeLookupListener (this);
}

As you did in the previous section, create a new module in the parent folder. Type MyEditor as the Project Name.

As you did in the previous section, you need to add the MyEditor module as a dependency of the app project, so that it will be deployed when you run the application.

As you did in the previous section, you need to add a dependency on the API module, so that you can use its public packages.

As you did in the previous section, create a new window in the MyEditor module. Set its position to "editor". Type MyEditor as the Class Name Prefix.

Check that the result of the steps you have taken so far match the screenshot below:

Figure 20. Source tree with new Window class

Use the Palette to drag and drop a Text Field onto the window:

Figure 21. Adding a text field to the window

Switch to the Source tab. At the end of the constructor in the window, include the following code:

Event obj = new Event();
associateLookup(Lookups.singleton(obj));

jTextField1.setText("Event #" + obj.getIndex() + " created at " + obj.getDate());

setDisplayName("MyEditor " + obj.getIndex());

Change the @TopComponent.OpenActionRegistration so that no preferredId is defined, as shown below, which means that a new Editor window will open whenever you choose Window | Editor in the menubar:

@TopComponent.OpenActionRegistration(displayName = "#CTL_MyEditorAction")

Right-click app project and choose Run. The application starts up, consisting of the NetBeans Platform, together with the custom modules you created.

The MyViewer window opens when the application starts and displays the two labels. You can now choose MyEditor from the Window menu, multiple times, to open multiple MyEditor components in the editor area. The MyViewer window will display the details of the currently selected MyEditor component.

Figure 22. Final result: running the application