One major difference between developing a NetBeans Platform application and a monolithic Java application is that there's no main method. This sometimes leaves developers wondering where they can insert their own code. This article describes some places where this is possible.

Although a bit drastic for most cases, you can replace the main class used to start NetBeans with your own class and then delegate back to NetBeans normal main class. This offers you a hook early in the startup sequence without having to modify the launchers or shell scripts.

Any module may provide a ModuleInstall class. The validate method will be called before your module is even loaded, so it's the first module-level hook typically available in the startup sequence. Note that many services and classes offered by the platform are unlikely to be initialized at this point.

A short time afterwards, the restored() method will be called on each ModuleInstall class. More services and classes will be initialized at this point than with the validate() method, but the GUI will probably not yet be realized. You can post some code to be executed when the UI is fully loaded like this:

    @Override
    public void restored() {
        WindowManager.getDefault().invokeWhenUIReady(
           new Runnable() {
              public void run() {
                 // any code here will be run with the UI is available
                 SomeTopComponent.findInstance().open();
              }
        });
    }

Note that providing a ModuleInstall class will degrade overall startup time somewhat, but as long as you don't overuse ModuleInstall classes and take care to execute any long-running tasks from its methods in a background thread, you should be OK.

Another major class in platform development is the TopComponent class. It offers several method which allow you to hook into its lifecycle.

Here is the sequence of events you can hook into for when a TopComponent is opened:

1. JComponent.addNotify
2. TopComponent.componentOpened
3. TopComponent.componentShowing
4. TopComponent.componentActivated

When you set focus on a TopComponent, the componentActivated method is called. Likewise, the componentDeactivated method is called when focus is moved away from that TopComponent.

Here is the sequence of events you can hook into for when a TopComponent is closed:

1. TopComponent.canClose
2. JComponent.removeNotify
3. TopComponent.componentHidden
4. TopComponent.componentDeactivated
5. TopComponent.componentClosed

Note that you can return false from TopComponent.canClose to prevent the TopComponent from being closed at all.

The ModuleInstall class offers two methods which let you plug into the exit sequence. The closing method is called first and requires that you return a boolean value. If true, then your module agrees to be closed, but if false, then you will prevent the exit sequence from continuing. The close method is called after all ModuleInstall classes return true from the closing method and is the final hook in which modules can participate in the application's lifecycle.

From http://wiki.netbeans.org/NetBeansDeveloperFAQ