Descending Number Triangle in Java

What You’ll Learn

The descending number triangle pattern is the classic first console pattern: nested loops, System.out.print vs newline, and a clear visual result. This tutorial covers the shape rule, loop structure, a live preview, algorithm steps, worked Java examples, edge cases, and complexity.

📝 Problem & Approach

Given a positive integer rows, print a descending number triangle: each row i shows digits 1 through i, with the outer loop counting from rows down to 1.

// First 5 rows (conceptual shape)
// 12345
// 1234
// 123
// 12
// 1

Inputs & Outputs

Minimal workflow

for i from rows down to 1:
    for j from 1 to i:
        print j (no newline)
    print newline

Approach comparison

🔮 Live Preview

Choose a row count between 1 and 20 and draw the descending number triangle in the browser.

Press "Draw pattern".

Examples Gallery

Three complete Java programs — fixed row count, Scanner input, and a char-cast shortcut. Click View Output to reveal sample console results.

public class DescendingNumberTriangle {
    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();
        }
    }
}

12345
1234
123
12
1

import java.util.Scanner;

public class DescendingNumberTriangleInput {
    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();
    }
}

Enter the number of rows: 7
1234567
123456
12345
1234
123
12
1

public class DescendingNumberChar {
    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((char)('0' + j));
            System.out.println();
        }
    }
}

12345
1234
123
12
1

🔎 Worked Walkthrough — rows = 4

Trace each outer-loop value of i (counting down) and count how many digits the inner loop prints.

Total digit prints: 1 + 2 + 3 + 4 = 10 = 4×5/2.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

💡 Best Practices