Nested For Loops - understanding them

[Steve Jensen]

I've been trying to understand just how nested for loops work , so I thought i'd devise a simple one of my own, as in the code below:-

class numbers
{
int a = 0;
   public static void main (String [] args)
   {
    for ( int i = 0 ; i < 5 ; i++ )  // begginning of outermost loop no. of times whole thing repeats itself
    {
       for ( int k = 0 ; k < 1 ; k++ )  // after how many loops 'three appears'
        {
          for ( int j = 0 ; j < 2 ; j++ )  // no. of times 'one' appears
           {
               System.out.println(" one ");
           }
        System.out.println(" two ");
        }
        System.out.println(" three ");
    } // end of outermost loop
   }

}

The thing is, I think the comments i've inserted next to the loops are indicative of their function , but, for example, how can I change this code, so that the word 'two', appears twice, i.e., like
one
one
two
two
I suppose this all stems from my misunderstanding of the whole concept, right?
(Marilyn added code tags to preserve formatting)
[ December 01, 2002: Message edited by: Marilyn de Queiroz ]

[Marilyn de Queiroz]

class numbers
{
    
    public static void main( String [] args )
    {
        // beginning of outermost loop/number of times whole thing repeats itself
        // "three" is printed just before each time 'i' is incremented
        for ( int i = 0 ; i < 5 ; i++ )  
        {
            // "two" is printed each time just before 'k' is incremented
            for ( int k = 0 ; k < 1 ; k++ )  
            {
                // "one" is printed each time just before 'j' is incremented
                for ( int j = 0 ; j < 2 ; j++ )
                {
                    System.out.println(" one ");
                }
                System.out.println(" two ");
            }
            System.out.println(" three ");
        } // end of outermost loop
    }
    
}  

Code to print
one
one
two
two
would look like:

class numbers
{
    
    public static void main( String [] args )
    {
        // beginning of outermost loop/number of times whole thing repeats itself
        // "three" is printed just before each time 'i' is incremented
        for ( int i = 0 ; i < 5 ; i++ )  
        {
            // "one" is printed each time just before 'j' is incremented
            for ( int j = 0 ; j < 2 ; j++ )
            {
                System.out.println(" one ");
            }
            // "two" is printed each time just before 'k' is incremented
            for ( int k = 0 ; k < 2 ; k++ )  
            {
                System.out.println(" two ");
            }
            System.out.println(" three ");
        } // end of outermost loop
    }
    
}  

[ December 01, 2002: Message edited by: Marilyn de Queiroz ]

[Bert Bates]

Notice that Marilyn 'unnested' the inner-most for loop to get 'two' to print twice in a row. Think of the nested loops as wheels on an odometer. The outer loop is the most significant number (leftmost), and the inner-most loop is the least significant (in this case the tenths of a mile). The farther right the digit, the more often it spins before the leftmost (outer) loops will increment.