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Java Program to Print Right Pascal Triangle Character Pattern

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In this program we print a right Pascal triangle of letters: the rows grow from A to A B C D E and then shrink back to A, which looks like a triangle pointing to the right.

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. Java stores a char as a number, so adding to 'A' and casting back with (char) gives the following letters.

1. The Pattern

For 5 rows the program prints:

Pattern
A
A B
A B C
A B C D
A B C D E
A B C D
A B C
A B
A

2. How the Program Works

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

LineLeading spacesPrinted after the spaces
10A
20A B
30A B C
40A B C D
50A B C D E
60A B C D
70A B C
80A B
90A
  • Both parts print row letters, starting at A, each followed by a space.
  • Step 1 counts row up from 1 to numberOfRows.
  • Step 2 counts row down from numberOfRows - 1 to 1. It starts one row lower so the longest row is printed only once.
  • System.out.println() moves to the next line after each row.

3. Java Program

Pattern17.java 
public class Pattern17 {
    public static void main(String[] args) {
        int numberOfRows = 5;

        // Step 1: rows get longer, up to numberOfRows letters
        for (int row = 1; row <= numberOfRows; row++) {
            for (int column = 1; column <= row; column++) {
                System.out.print((char) ('A' + column - 1) + " ");
            }
            System.out.println();
        }

        // Step 2: rows get shorter again, without repeating the longest row
        for (int row = numberOfRows - 1; row >= 1; row--) {
            for (int column = 1; column <= row; column++) {
                System.out.print((char) ('A' + column - 1) + " ");
            }
            System.out.println();
        }
    }
}
Output
A
A B
A B C
A B C D
A B C D E
A B C D
A B C
A B
A

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.

Pattern17Input.java 
import java.util.Scanner;

public class Pattern17Input {
    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();

        // Step 1: rows get longer, up to numberOfRows letters
        for (int row = 1; row <= numberOfRows; row++) {
            for (int column = 1; column <= row; column++) {
                System.out.print((char) ('A' + column - 1) + " ");
            }
            System.out.println();
        }

        // Step 2: rows get shorter again, without repeating the longest row
        for (int row = numberOfRows - 1; row >= 1; row--) {
            for (int column = 1; column <= row; column++) {
                System.out.print((char) ('A' + column - 1) + " ");
            }
            System.out.println();
        }
    }
}
Output (with sample input)
Enter the number of rows: 4
A
A B
A B C
A B C D
A B C
A B
A
Note: there are only 26 letters. Past Z, (char) ('A' + 26) is [, not a letter, so keep the number of rows small enough that the pattern never needs a letter after Z.

5. Summary

  • The outer loop picks the row; the inner loops print the spaces and the letters for that row.
  • (char) ('A' + k) gives the letter k places after A.
  • Keep numberOfRows in a variable, so the same program can print the pattern in any size.

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