By qualifying the outer class you gain access to its static members, e.g.
public class Outer
{
public static void hi()
{
System.out.printf("hi from Outer\n");
}
public static class Inner
{
public static void hello()
{
System.out.printf("hello from Inner and ");
Outer.hi();
}
}
public static void main(String [] arg)
{
Inner.hello();
}
}