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Java Program to Print Downward Left Triangle Star Pattern

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In this program we print a downward left triangle of stars. The first row has five stars, each row after it has one star fewer, and one more space in front keeps the right edge straight.

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*
  • The outer loop runs once for each row, from 1 to numberOfRows.
  • The first inner loop prints row - 1 spaces.
  • The second inner loop prints numberOfRows - row + 1 stars.
  • System.out.println() moves to the next line after each row.

3. Java Program

DownwardLeftTriangleStarPattern.java 
public class DownwardLeftTriangleStarPattern {
    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 spaces
            for (int column = 1; column < row; column++) {
                System.out.print(" ");
            }
            // inner loop to print the stars
            for (int column = 1; column <= numberOfRows - row + 1; column++) {
                System.out.print("*");
            }
            // move to the next line
            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.

DownwardLeftTriangleStarPatternInput.java 
import java.util.Scanner;

public class DownwardLeftTriangleStarPatternInput {
    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 spaces
            for (int column = 1; column < row; column++) {
                System.out.print(" ");
            }
            // inner loop to print the stars
            for (int column = 1; column <= numberOfRows - row + 1; column++) {
                System.out.print("*");
            }
            // move to the next line
            System.out.println();
        }
    }
}
Output (with sample input)
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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