Java Program to Print Right Triangle Number Pattern - 1

In this program we print a right triangle number pattern. Each row starts at 1 and counts up to the row number, so every row is one number longer than the row above it.

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:

1
1 2
1 2 3
1 2 3 4
1 2 3 4 5

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 the numbers from 1 to row, each followed by a space.
• System.out.println() moves to the next line after each row.

3. Java Program

public class Pattern1 {
    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 numbers 1 to row
            for (int column = 1; column <= row; column++) {
                System.out.print(column + " ");
            }
            // move to the next line
            System.out.println();
        }
    }
}

1
1 2
1 2 3
1 2 3 4
1 2 3 4 5

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 Pattern1Input {
    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 numbers 1 to row
            for (int column = 1; column <= row; column++) {
                System.out.print(column + " ");
            }
            // move to the next line
            System.out.println();
        }
    }
}

Enter the number of rows: 6
1
1 2
1 2 3
1 2 3 4
1 2 3 4 5
1 2 3 4 5 6

5. Summary

• The outer loop picks the row; the inner loops print the spaces and the numbers for that row.
• Work out how many spaces and which numbers 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

• Java Program to Print Right Triangle Number Pattern - 2
• Java Program to Print Right Triangle Number Pattern - 3
• All Java Pattern Programs