Control Flow | Engineering Interview Kit

TL;DR

Control flow statements break up the flow of execution by employing decision-making, looping, and branching, enabling your program to conditionally execute particular blocks of code.

Decision Making: if, else, switch
Looping: for, while, do-while
Branching: break, continue, return

Concept

By default, statements in a script are executed sequentially from top to bottom. Control flow dictates how this top-to-bottom sequence is altered.

Switch Statement (Java 14+)

The traditional switch has been upgraded in modern Java (Java 14+) with switch expressions, avoiding the need for break statements and allowing it to return a value directly.

Enhanced For Loop

The “for-each” loop is used exclusively to loop through elements in an array or a Collection (like a List).

Examples

public class ControlFlow {
    public static void main(String[] args) {
        // 1. Enhanced For-Loop
        String[] fruits = {"Apple", "Banana", "Cherry"};
        for (String fruit : fruits) {
            System.out.println(fruit);
        }
        
        // 2. Modern Switch Expression (Java 14+)
        String day = "MONDAY";
        boolean isWeekend = switch (day) {
            case "SATURDAY", "SUNDAY" -> true;
            case "MONDAY", "TUESDAY", "WEDNESDAY", "THURSDAY", "FRIDAY" -> false;
            default -> throw new IllegalArgumentException("Invalid day: " + day);
        };
    }
}

Interview Questions

Q: What is the difference between while and do-while?
A: A while loop checks the condition before executing the block. If the condition is false initially, the block is never executed. A do-while loop executes the block first, and then checks the condition. Therefore, a do-while loop will always execute at least once.

Q: Can we use strings in a switch case?
A: Yes. Prior to Java 7, switch only worked with byte, short, char, and int (and their wrappers). Since Java 7, you can use String objects in a switch statement. Since Java 14, you can also use Switch Expressions.