Method

Here is the definition, again:

• if N is 1, stop
• if N is even, replace it with N/2
• if N is odd, replace it with 3*N + 1

And here is a method:

  static void hail( long N )
  {
    System.out.print( N + ", ");
    
    if (  )
      return;
      
    else if (  )
    
      hail(  );
      
    else
      hail(  );
  }

The method prints out the current N, then advances to the next by calling itself. When it hits one, it returns to its caller, which returns to its caller, and so on up the chain until the first activation.