How do I compute this weird pattern? Java nested loop exercise

I'm computing a star pattern with the variable num_star. This num_star (greater than 2) determines the maximum number of characters.

No need for complications, just simple logic and for-loop as I'm learning.

My logic: Odd number prints 1 star first. Even number prints 2 stars first.

Example: num_star = 3

 *
***
***
 *

num_star = 4

 **
****
****
 **

num_star = 5

  *
*****
 ***
*****
  *

num_star = 6

  **
******
 ****
******
  **

num_star = 7

   *
  ***
*******
 *****
*******
  ***
   *

num_star = 8

   **
  ****
********
 ******
********
  ****
   **

num_star = 9

    *
   ***
*********
 *******
  *****
 *******
*********
   ***
    *

I've tried the Triangle method on Google but I have no idea on how to compute/logic those in the middle..

My code:

int num_star = 3;

    if (num_star%2==1) {
        for(int i = 1; i< num_star; i++){

            for(int j = i; j< num_star; j++){
                System.out.print(" ");
            }
            for(int k = 1; k<(2*i); k++){
                System.out.print("*");
            }
        System.out.println();
    }

        for (int i = num_star-1; i > 0; i--){

            for (int j = num_star; j > i; j--){
                System.out.print(" ");
            }
            for (int k = (2*i); k > 1; k--){
                System.out.print("*");
            }

        System.out.println();
    }
}