Print Pyramid Star Pattern in Java

Topic

In this program, we are required to print a pyramid-shaped pattern using stars (*) in Java. A pyramid pattern is one where each row has an increasing number of stars centered horizontally, forming a triangle. This is a classic pattern printing program asked in Java interviews to test understanding of loops and logic building.

Examples

Input: 4

Output:
   *
  ***
 *****
*******

Input: 1

Output:
*

Input: 0

Output:
(no output)

Explanation:

• Each row contains increasing odd numbers of stars: 1, 3, 5, ...
• Spaces are used on the left side to align the stars in a centered pyramid.

Interviewer Expectations

The interviewer wants to assess your understanding of:

• Nested loops (outer loop for rows, inner loops for spaces and stars)
• Loop conditions and counters
• Control flow and formatting console output

Approach

We need to print N rows. For each row:

1. Print (N - row) spaces to shift stars to the right.
2. Print (2 * row - 1) stars to form the pyramid structure.

This means for row 1: 3 spaces + 1 star, row 2: 2 spaces + 3 stars, etc.

Dry Run (N = 4)

Row 1: spaces = 3, stars = 1 → "   *"
Row 2: spaces = 2, stars = 3 → "  ***"
Row 3: spaces = 1, stars = 5 → " *****"
Row 4: spaces = 0, stars = 7 → "*******"

Java Program

public class PyramidPattern {
  public static void main(String[] args) {
    int rows = 4;

    for (int i = 1; i <= rows; i++) {
      // print spaces
      for (int j = 1; j <= rows - i; j++) {
        System.out.print(" ");
      }

      // print stars
      for (int k = 1; k <= 2 * i - 1; k++) {
        System.out.print("*");
      }

      // move to next line
      System.out.println();
    }
  }
}

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

Practice Pyramid Pattern

Possible Followup Questions with Answers

1. How to make the pyramid pattern upside down?

You can reverse the loop — start from the max row down to 1 and adjust space and star counts accordingly.

for (int i = rows; i >= 1; i--) {
  // spaces
  for (int j = 1; j <= rows - i; j++) {
    System.out.print(" ");
  }
  // stars
  for (int k = 1; k <= 2 * i - 1; k++) {
    System.out.print("*");
  }
  System.out.println();
}

2. How to print a half pyramid (right-angled triangle)?

Remove space printing, and print stars only for the current row:

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

3. How to take input from the user instead of hardcoding?

Scanner sc = new Scanner(System.in);
int rows = sc.nextInt();

Then use the same loop structure with the user-defined value.