Java Program to Print Right Triangle Star Pattern

In this program we print a right triangle of stars. The first row has one star, and every row after it has one more.

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:

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

2. How the Program Works

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

• The outer loop runs once for each row, from 1 to numberOfRows.
• The inner loop prints row stars, each followed by a space.
• System.out.println() moves to the next line after each row.

3. Java Program

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

        // outer loop for the rows
        for (int row = 1; row <= numberOfRows; row++) {
            // inner loop to print the stars
            for (int column = 1; column <= row; column++) {
                System.out.print("* ");
            }
            // move to the next line
            System.out.println();
        }
    }
}

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

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.

import java.util.Scanner;

public class RightTriangleStarPatternInput {
    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();

        // outer loop for the rows
        for (int row = 1; row <= numberOfRows; row++) {
            // inner loop to print the stars
            for (int column = 1; column <= row; column++) {
                System.out.print("* ");
            }
            // move to the next line
            System.out.println();
        }
    }
}

Enter the number of rows: 6
*
* *
* * *
* * * *
* * * * *
* * * * * *

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.

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• Java Program to Print Left Triangle Star Pattern
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• Java Program to Print Downward Pyramid Star Pattern
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