🛡️ What is Control Flow?

Control flow refers to the order in which statements are executed in a program. In Java, logic is controlled using decision-making, looping, and branching statements. Without control flow, programs would execute linearly from top to bottom.

⏰ When to Use

• Conditional Logic: Using if, else, and switch to execute code based on specific conditions.
• Iteration: Using for, while, and do-while to repeat tasks until a condition is met.
• Branching: Using break, continue, and return to alter the loop's natural course.

📊 Complexity & Performance

• Decision Trees: if-else chains have $O(n)$ complexity in the worst case, whereas switch statements can be optimized by the JVM into a branch table ($O(1)$) for dense case values.
• Loops: Iterating through a collection of size $N$ is $O(N)$. Nested loops lead to $O(N^2)$ or higher, which should be avoided in performance-critical sections.

💻 Code Example: Dynamic Evaluation

java Standard
public class ControlFlowDemo {
    public static void main(String[] args) {
        int score = 85;
        
        // 1. Ternary Operator (Sugar for simple if-else)
        String status = (score >= 60) ? "Pass" : "Fail";
        
        // 2. Structured Choice (Switch-Case)
        char grade;
        switch (score / 10) {
            case 10:
            case 9:  grade = 'A'; break;
            case 8:  grade = 'B'; break;
            case 7:  grade = 'C'; break;
            default: grade = 'F';
        }
        
        // 3. Enhanced For-Loop (Iteration)
        int[] milestones = {10, 20, 30, 40, 50};
        for (int m : milestones) {
            if (m > score) continue; // Skip if milestone not reached
            System.out.println("Milestone achieved: " + m);
        }
    }
}

⚠️ Interview Pitfalls

1. Forget the break: In a switch statement, forgetting a break results in "fall-through," where subsequent cases execute even if their conditions aren't met.
2. Infinite Loops: Always ensure the loop condition eventually becomes false. A common bug is modifying the iterator inside the loop in a way that prevents termination.
3. Floating Point Comparison: Never use == to compare float or double in loop conditions or if statements due to precision errors. Use a threshold (epsilon).
4. Equality vs. Reference: When comparing Strings in if statements, use .equals() instead of ==. The latter checks memory address, not content.