Printing a Diamond Star/Rhombus Dynamically in Java

import java.io.BufferedReader;
import java.io.InputStreamReader;
public class DiamondStar {
    //import java.io.*;

    static int e;
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Enter a  number");
        String q = br.readLine();
        int z = Integer.parseInt(q);

        String j = " ";
        String k = "                                ";
        int g = z / 2;
        int p = g - 1;
        int r = 0;
        String s = "**";
        String m = "*";
        for (int i = 1; i < z; i++) {

            if (i <= g) {
                j = k.substring(0, (z - g) - i) + j.trim() + s;
                //j=j+s;
                System.out.println(j.substring(0, j.length() - 1));
                e = j.length();
            } else {

                String w = k.substring(0, r + 1) + j.substring(0, z - i) + j.substring(0, z - i - 1);
                System.out.println(w);
                e--;
                r++;
            }
        }
    }
}