Java For Loop: Counter-Controlled Iteration & Nested Patterns

The for loop is a counter-controlled iteration statement widely favored when the exact number of execution repetitions is known prior to loop entry.

Syntax and Execution Flow

// For Loop Syntax:
for (initialization; boolean_condition; update_step) {
    // Loop body statements
}

Step-by-Step Execution Lifecycle:

1. Step 1 (Initialization): Executes exactly once upon loop entry (e.g. int i = 1).
2. Step 2 (Condition Evaluation): Evaluates boolean_condition. If true, proceeds to body. If false, loop terminates immediately.
3. Step 3 (Body Execution): Executes all statements enclosed within the block.
4. Step 4 (Update Step): Increments or updates the loop variable (e.g. i++).
5. Step 5: Jumps back to Step 2.

Nested For Loops: Star Pyramid Pattern Program

Nested for loops (a loop residing inside an outer loop) are a staple in university practical exams for generating coordinate grids and geometric shapes:

public class PyramidPattern {
    public static void main(String[] args) {
        int rows = 5;

        // Outer loop controls number of rows
        for (int i = 1; i <= rows; i++) {
            // Inner loop 1: Prints leading spaces for centering
            for (int space = 1; space <= rows - i; space++) {
                System.out.print(" ");
            }
            // Inner loop 2: Prints asterisks
            for (int star = 1; star <= (2 * i - 1); star++) {
                System.out.print("*");
            }
            // Move to next line
            System.out.println();
        }
    }
}

Output:

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

for (int i = 0, j = 10; i < j; i++, j--) {
    System.out.println("i=" + i + ", j=" + j);
}