00:00

Help Us Improve

We're sorry this tutorial wasn't helpful. Please tell us what we can do better.

Java Program to Print Sandglass Star Pattern

Last updated:

In this program we print a sandglass (hourglass) of stars. The top half narrows from five stars to one, and the bottom half widens back out.

Like every pattern program, it is built from nested loops: the outer loop picks the row, and the inner loops print what goes on that row.

1. The Pattern

For 5 rows the program prints:

Pattern
* * * * *
 * * * *
  * * *
   * *
    *
    *
   * *
  * * *
 * * * *
* * * * *

2. How the Program Works

Here is what each printed line is made of when numberOfRows is 5:

LineLeading spacesPrinted after the spaces
10* * * * *
21* * * *
32* * *
43* *
54*
64*
73* *
82* * *
91* * * *
100* * * * *
  • Both parts print row - 1 spaces and then numberOfRows - row + 1 stars as "* ".
  • Step 1 counts row up from 1 to numberOfRows, so the rows get shorter.
  • Step 2 counts row back down from numberOfRows to 1, so the rows get longer again. Both parts print the one-star row, so it appears twice in the middle.
  • System.out.println() moves to the next line after each row.

3. Java Program

SandglassStarPattern.java 
public class SandglassStarPattern {
    public static void main(String[] args) {
        int numberOfRows = 5;

        // Step 1: top half, rows get shorter
        for (int row = 1; row <= numberOfRows; row++) {
            for (int column = 1; column < row; column++) {
                System.out.print(" ");
            }
            for (int column = row; column <= numberOfRows; column++) {
                System.out.print("* ");
            }
            System.out.println();
        }

        // Step 2: bottom half, rows get longer again
        for (int row = numberOfRows; row >= 1; row--) {
            for (int column = 1; column < row; column++) {
                System.out.print(" ");
            }
            for (int column = row; column <= numberOfRows; column++) {
                System.out.print("* ");
            }
            System.out.println();
        }
    }
}
Output
* * * * *
 * * * *
  * * *
   * *
    *
    *
   * *
  * * *
 * * * *
* * * * *

4. Print the Pattern for Any Number of Rows

To let the user choose the size of the pattern, read the number of rows with a Scanner. The loops stay the same.

SandglassStarPatternInput.java 
import java.util.Scanner;

public class SandglassStarPatternInput {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the number of rows: ");
        int numberOfRows = scanner.nextInt();
        scanner.close();

        // Step 1: top half, rows get shorter
        for (int row = 1; row <= numberOfRows; row++) {
            for (int column = 1; column < row; column++) {
                System.out.print(" ");
            }
            for (int column = row; column <= numberOfRows; column++) {
                System.out.print("* ");
            }
            System.out.println();
        }

        // Step 2: bottom half, rows get longer again
        for (int row = numberOfRows; row >= 1; row--) {
            for (int column = 1; column < row; column++) {
                System.out.print(" ");
            }
            for (int column = row; column <= numberOfRows; column++) {
                System.out.print("* ");
            }
            System.out.println();
        }
    }
}
Output (with sample input)
Enter the number of rows: 4
* * * *
 * * *
  * *
   *
   *
  * *
 * * *
* * * *

5. Summary

  • The outer loop picks the row; the inner loops print the spaces and the stars for that row.
  • Work out how many spaces and stars each row needs, then write one inner loop for each.
  • Keep numberOfRows in a variable, so the same program can print the pattern in any size.

Related Programs