Java Program to Print Right Triangle Star Pattern

A right triangle star pattern is a triangle made of asterisks * where the number of stars in each row increases from 1 up to n.

Example:

Input : n = 5
Output:
*
* *
* * *
* * * *
* * * * *

Method 1: Using Nested Loops (Iterative Approach)

This is the most common approach. The outer loop iterates over rows, and the inner loop prints stars in each row.

Java

public class RightTriangleStarPattern {
    public static void main(String[] args) {
        int rows = 5; 
        
        for (int i = 1; i <= rows; i++) {       // Outer loop for rows
            for (int j = 1; j <= i; j++) {     // Inner loop for stars
                System.out.print("* ");
            }
            System.out.println();               // Move to next line
        }
    }
}

Output

* 
* * 
* * * 
* * * * 
* * * * *

Explanation:

The outer loop runs from 1 to rows and controls the number of rows printed.
The inner loop runs from 1 to i, printing one * for each column in the current row.
After each row is printed, println() moves the cursor to the next line.

Method 2: Using Recursion

We can also print the triangle recursively by printing stars row by row.

Java

class RightTriangleRecursive {

    // Prints stars in a single row
    public static void printStars(int stars) {
        if (stars == 0) return;
        System.out.print("* ");
        printStars(stars - 1);
    }
    // Prints rows recursively
    public static void printTriangle(int currentRow, int totalRows) {
        if (currentRow > totalRows) return;
        printStars(currentRow);
        System.out.println();
        printTriangle(currentRow + 1, totalRows);
    }
    public static void main(String[] args) {
        int n = 5;
        printTriangle(1, n);
    }
}

Output

* 
* * 
* * * 
* * * * 
* * * * *

Explanation:

The printStars() method prints stars in a single row using recursion until the count becomes zero.
The printTriangle() method recursively prints each row by increasing the current row count.
Recursion terminates when the current row exceeds the total number of rows.

Method 3: Using a Single Loop with String Concatenation

This method builds each row using string concatenation.

Java

public class RightTriangleString {
    public static void main(String[] args) {
        int n = 5;
        String row = "*";

        for (int i = 1; i <= n; i++) {
            System.out.println(row);
            row += "*"; // Add one more star for next row
        }
    }
}

Output

*
**
***
****
*****

Explanation:

A string variable row is initialized with one *.
In each iteration, the current value of row is printed.
One additional * is concatenated to the string for the next row.

Method 4: Using a Single Loop with numStars Counter

This approach keeps a counter for stars per row.

Java

public class RightTriangleCounter {
    public static void main(String[] args) {
        int n = 5;
        int numStars = 1;

        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= numStars; j++) {
                System.out.print("* ");
            }
            numStars++;
            System.out.println();
        }
    }
}

Output

* 
* * 
* * * 
* * * * 
* * * * *

Explanation:

The variable numStars keeps track of how many stars should be printed in each row.
The inner loop prints stars equal to the value of numStars.
After printing each row, numStars is incremented to increase stars for the next row.

Java Program to Print Right Triangle Star Pattern

Method 1: Using Nested Loops (Iterative Approach)

Method 2: Using Recursion

Method 3: Using a Single Loop with String Concatenation

Method 4: Using a Single Loop with numStars Counter

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