How to make a splash screen for GUI?

Hi there I'm new to GUIs in Java and was trying to make a splash screen or an image appear for 3 seconds. Then after that it it will go onto my main program. Does anyone have an ideas how to do this or can link me to any tutorials?

So far I have done this but not sure where to go from here.

public static void main(String[] args)
{
    splashInit();           // initialize splash overlay drawing parameters
    appInit();              // simulate what an application would do 
}