Java Program to Print Pyramid Pattern

You can print a pyramid pattern in Java using nested for loops where the outer loop controls the rows and the inner loops print spaces and stars, like for (int i = 1; i <= n; i++) { for (int j = n; j > i; j--) System.out.print(" "); for (int k = 1; k <= 2*i-1; k++) System.out.print("*"); System.out.println(); }.

Examples

Inputn = 3

Output * *** *****

Inputn = 5

Output * *** ***** ******* *********

Inputn = 1

Output*

How to Think About It

To print a pyramid pattern, think of each row having spaces first, then stars. The number of spaces decreases as you go down, and the number of stars increases by two each row. Use one loop for rows, one loop for spaces, and one loop for stars.

Algorithm

1

Get the number of rows (n) as input.

2

For each row from 1 to n:

3

Print (n - current row) spaces.

4

Print (2 * current row - 1) stars.

5

Move to the next line.

Code

java

public class PyramidPattern {
    public static void main(String[] args) {
        int n = 5; // number of rows
        for (int i = 1; i <= n; i++) {
            for (int j = n; j > i; j--) {
                System.out.print(" ");
            }
            for (int k = 1; k <= 2 * i - 1; k++) {
                System.out.print("*");
            }
            System.out.println();
        }
    }
}

Output

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

Dry Run

Let's trace n=3 through the code

1

Row 1

Print 2 spaces, then 1 star: ' *'

2

Row 2

Print 1 space, then 3 stars: ' ***'

3

Row 3

Print 0 spaces, then 5 stars: '*****'

Row (i)	Spaces (n - i)	Stars (2*i - 1)
1	2	1
2	1	3
3	0	5

Why This Works

Step 1: Outer loop controls rows

The outer for loop runs from 1 to n, each iteration prints one row of the pyramid.

Step 2: Print spaces before stars

The first inner loop prints spaces to align stars in a pyramid shape, decreasing as row number increases.

Step 3: Print stars for pyramid

The second inner loop prints stars, increasing by two each row to form the pyramid shape.

Alternative Approaches

Using while loops

java

public class PyramidPattern {
    public static void main(String[] args) {
        int n = 5;
        int i = 1;
        while (i <= n) {
            int j = n;
            while (j > i) {
                System.out.print(" ");
                j--;
            }
            int k = 1;
            while (k <= 2 * i - 1) {
                System.out.print("*");
                k++;
            }
            System.out.println();
            i++;
        }
    }
}

Using while loops instead of for loops gives the same result but is less concise.

Using String.repeat() (Java 11+)

java

public class PyramidPattern {
    public static void main(String[] args) {
        int n = 5;
        for (int i = 1; i <= n; i++) {
            System.out.print(" ".repeat(n - i));
            System.out.print("*".repeat(2 * i - 1));
            System.out.println();
        }
    }
}

Using <code>String.repeat()</code> makes code shorter and clearer but requires Java 11 or newer.

Complexity: O(n^2) time, O(1) space

Time Complexity

The program uses nested loops: the outer loop runs n times and inner loops run up to n times, resulting in O(n^2) time.

Space Complexity

Only a few variables are used; no extra space proportional to input size, so space complexity is O(1).

Which Approach is Fastest?

Using String.repeat() is concise but similar in performance; while loops are less readable but equivalent in speed.

Approach	Time	Space	Best For
For loops	O(n^2)	O(1)	Readability and clarity
While loops	O(n^2)	O(1)	When for loops are unfamiliar
String.repeat()	O(n^2)	O(1)	Concise code with Java 11+