To get an instance of your plugin you can do it like this:
PluginHandle handle = this.bridge.getPlugin("MyPlugin");
if (handle == null) {
return;
}
MyPlugin myPlugin = (MyPlugin) handle.getInstance();
myPlugin.doSomething();
Also, from MainActivity.java you can use the bridge object to fire javascript events with this.bridge.triggerDocumentJSEvent, this.bridge.triggerWindowJSEvent and this.bridge.triggerJSEvent methods without a plugin.