Descending Number Triangle in Java
What You’ll Learn
How to print a descending number triangle in Java using nested for loops. Each row starts at 1 and prints up to a decreasing limit: rows, rows-1, ..., down to 1.
This pattern is a simple way to understand how the outer loop controls rows and the inner loop controls how many numbers appear per row.
⭐ Pattern Output
For rows = 5, the pattern looks like this:
12345
1234
123
12
1Complete Java Program
The outer loop starts from rows and counts down. The inner loop prints numbers from 1 to the current row limit.
public class Main {
public static void main(String[] args) {
int rows = 5;
for (int i = rows; i >= 1; i--) {
for (int j = 1; j <= i; j++) {
System.out.print(j);
}
System.out.println();
}
}
}🧠 How It Works
Choose the row count
int rows = 5; sets how many lines will be printed.
Outer loop (descending rows)
for (int i = rows; i >= 1; i--) controls the triangle height and ensures each next row has one fewer number than the previous.
Inner loop (print 1..i)
for (int j = 1; j <= i; j++) prints digits from 1 up to the current row limit i using System.out.print(j).
New line
System.out.println(); moves to the next row after each line.
Descending number triangle
Total numbers printed: 1+2+…+n = n(n+1)/2, so time complexity is O(n²) for n rows.
Variation — User Input Version
Let the user decide the number of rows at runtime using Scanner:
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.print("Enter the number of rows: ");
int rows = sc.nextInt();
for (int i = rows; i >= 1; i--) {
for (int j = 1; j <= i; j++) {
System.out.print(j);
}
System.out.println();
}
sc.close();
}
}💡 Tips for Enhancement
Try These
- Validate input (check
Scanner.hasNextInt()) before usingrows - Print the ascending triangle by counting the outer loop up
- Add spaces between numbers with
System.out.print(j + " ") - Right-align the triangle by printing leading spaces before each row
- Replace numbers with characters to create alphabet patterns
Avoid
- Forgetting
System.out.println()between rows - Using negative or zero rows without validating input
- Mixing row/column logic (keep the outer loop for rows)
- Closing
System.inwithScannerif you still need console input elsewhere in the same JVM run
Key Takeaways
The outer loop decreases the row length (from rows down to 1).
The inner loop prints numbers from 1 to the current row limit i.
Total printed digits follow the triangular number count: n(n+1)/2.
The same nested-loop idea applies to star triangles and alphabet triangles.
❓ Frequently Asked Questions
12345, then 1234, then 123, and so on until 1.i (from rows down to 1). The inner loop prints j from 1 to i, then calls System.out.println().for (int i = 1; i <= rows; i++) as the outer loop. Each row will then grow from 1 number up to rows numbers.Explore More Java Number Patterns!
From pyramids to Floyd’s triangle and beyond—practice nested loops with progressively richer patterns.
The total number of printed digits grows like a triangular number. If you print n rows, the total count is 1+2+…+n = n(n+1)/2. For n = 5, that’s 15 digits.
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