Receiving startup events in single instance mode

## Receiving startup events in single instance mode |

| If you have enabled the single instance mode for your executable, the application can only be started once. For a GUI application, the existing application window is brought to front when a user executes the launcher another time. However, you might want to receive notifications about multiple startups together with the command line parameters. If you have associated you executable with a file extension, you will likely want to handle multiple invocations in the same instance of your application. Alternatively, you might want to perform some action when another startup occurs.

| With the exe4j launcher API you can write a class that implements the `com.exe4j.Controller.StartupListener` interface and register it with `com.exe4j.Controller.registerStartupListener(StartupListener startupListener)`. Your implementation of `startupPerformed(String parameters)` of the `StartupListener` interface will then be notified if another startup occurs. The launcher API of exe4j is contained in `exe4jlib.jar` which can be found in the top level directory of your exe4j installation. Note: you do not have to add it to the classpath of your application and distribute it along with it, since that file is always contained in the executable.