Drawing a Diamond with User Input (not double of the user input)

So I've been trying to draw a Diamond shape in Java and I've got the top part of the diamond done but the bottom part is not printing as I want it to. Instead of decreasing towards the end, it stays the same or it increases as it go down.

import java.util.Scanner;

public class Q1_Diamond{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        System.out.print("How many lines? ");
        int lines = sc.nextInt();

        // Top half of Diamond
        for(int i = 0; i < lines/2; i++){
            for(int j = 0; j < (lines-1)-i; j++){
                System.out.print(" ");
            }

            for(int j = 0; j < i; j++){
                System.out.print("*");
            }

            for(int j = 0; j < i+1; j++){
                System.out.print("*");
            }
            System.out.println();
        }

        // Bottom half of Diamond
        // Even number of lines
        if(lines % 2 == 0){
            for(int k = 0; k < (lines/2); k++){

                for(int j = 0; j < (lines/2)+k; j++){
                    System.out.print(" ");
                }

                for(int j = 0; j < (lines/3 - 0.5f); j++){
                    System.out.print("*");
                }

                for(int j = 0; j < lines/2+1; j++){
                    System.out.print("*");
                }
                System.out.println();
            }
        }

        // Odd number of lines
        else{
            not done yet...
        }
    }
}

Solution

Remove the if condition (i.e. if(lines % 2 == 0)) for the lower half and simply repeat the same code as the upper half with the following loop declaration:

for (int i = lines % 2 == 0 ? lines / 2 - 1 : lines / 2; i >= 0; i--)

Complete code:

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("How many lines? ");
        int lines = sc.nextInt();

        // Top half of Diamond
        for (int i = 0; i < lines / 2; i++) {
            for (int j = 0; j < (lines - 1) - i; j++) {
                System.out.print(" ");
            }

            for (int j = 0; j < i; j++) {
                System.out.print("*");
            }

            for (int j = 0; j < i + 1; j++) {
                System.out.print("*");
            }
            System.out.println();
        }
        // Bottom half of Diamond
        for (int i = lines % 2 == 0 ? lines / 2 - 1 : lines / 2; i >= 0; i--)  {
            for (int j = 0; j < (lines - 1) - i; j++) {
                System.out.print(" ");
            }

            for (int j = 0; j < i; j++) {
                System.out.print("*");
            }

            for (int j = 0; j < i + 1; j++) {
                System.out.print("*");
            }
            System.out.println();
        }
    }
}

A sample run:

How many lines? 10
         *
        ***
       *****
      *******
     *********
     *********
      *******
       *****
        ***
         *

Another sample run:

How many lines? 11
          *
         ***
        *****
       *******
      *********
     ***********
      *********
       *******
        *****
         ***
          *

[Update]

You can extract the common code into a method e.g. printLine as shown below:

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("How many lines? ");
        int lines = sc.nextInt();

        // Top half of Diamond
        for (int i = 0; i < lines / 2; i++) {
            printLine(lines, i);
        }
        // Bottom half of Diamond
        for (int i = lines % 2 == 0 ? lines / 2 - 1 : lines / 2; i >= 0; i--) {
            printLine(lines, i);
        }
    }

    static void printLine(int lines, int i) {
        for (int j = 0; j < (lines - 1) - i; j++) {
            System.out.print(" ");
        }

        for (int j = 0; j < i; j++) {
            System.out.print("*");
        }

        for (int j = 0; j < i + 1; j++) {
            System.out.print("*");
        }
        System.out.println();
    }
}