Conditional Statements

# CHAPTER 7

Conditional Statements #

1. Introduction #

2. Learning Objectives #

• Use if, if-else, and else if statements.

• Implement nested conditions.

• Use the switch statement for multi-way branching.

• Build a grade evaluation system.

3. The if Statement #

int age = 20;
if (age >= 18) {
    System.out.println("You are an adult.");
}

4. The if-else Statement #

int temperature = 35;
if (temperature > 30) {
    System.out.println("It's hot outside!");
} else {
    System.out.println("The weather is pleasant.");
}

5. The else if Ladder #

int score = 75;
if (score >= 90) {
    System.out.println("Grade: A");
} else if (score >= 80) {
    System.out.println("Grade: B");
} else if (score >= 70) {
    System.out.println("Grade: C");
} else if (score >= 60) {
    System.out.println("Grade: D");
} else {
    System.out.println("Grade: F");
}

6. Nested if Statements #

int age = 25;
boolean hasLicense = true;

if (age >= 18) {
    if (hasLicense) {
        System.out.println("You can drive.");
    } else {
        System.out.println("Get a license first.");
    }
} else {
    System.out.println("You are too young to drive.");
}

7. The switch Statement #

int day = 3;
switch (day) {
    case 1:
        System.out.println("Monday");
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    case 3:
        System.out.println("Wednesday");
        break;
    case 4:
        System.out.println("Thursday");
        break;
    case 5:
        System.out.println("Friday");
        break;
    default:
        System.out.println("Weekend!");
}

Important: Without break, execution "falls through" to the next case!

8. Enhanced Switch (Java 14+) #

String day = "MONDAY";
String type = switch (day) {
    case "MONDAY", "TUESDAY", "WEDNESDAY", "THURSDAY", "FRIDAY" -> "Weekday";
    case "SATURDAY", "SUNDAY" -> "Weekend";
    default -> "Invalid";
};
System.out.println(type); // "Weekday"

9. Mini Project: Grade Evaluation System #

import java.util.Scanner;

public class GradeEvaluator {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        System.out.println("=== GRADE EVALUATION SYSTEM ===");
        System.out.print("Enter your score (0-100): ");
        int score = sc.nextInt();

        String grade;
        String remark;

        if (score < 0 || score > 100) {
            grade = "Invalid";
            remark = "Please enter a score between 0 and 100.";
        } else if (score >= 90) {
            grade = "A+";
            remark = "Outstanding! You are a top performer.";
        } else if (score >= 80) {
            grade = "A";
            remark = "Excellent work!";
        } else if (score >= 70) {
            grade = "B";
            remark = "Good job, keep improving!";
        } else if (score >= 60) {
            grade = "C";
            remark = "You passed. Study harder!";
        } else if (score >= 50) {
            grade = "D";
            remark = "Just passed. Needs improvement.";
        } else {
            grade = "F";
            remark = "Failed. Please retake the course.";
        }

        System.out.println("\n--- RESULT ---");
        System.out.println("Score:  " + score);
        System.out.println("Grade:  " + grade);
        System.out.println("Remark: " + remark);
        System.out.println("--------------");

        sc.close();
    }
}

10. Common Mistakes #

• Using = instead of ==: if (x = 5) assigns; if (x == 5) compares.

• Missing break in switch: Causes fall-through behavior.

• Comparing Strings with ==: Use .equals() for String comparison.

11. Exercises #

1. 1. Write a program that checks if a number is positive, negative, or zero.

1. 2. Build a simple calculator using switch-case (add, subtract, multiply, divide).

1. 3. Write a program that takes a month number (1-12) and prints the season.

12. MCQ Quiz with Answers #

13. Interview Questions #

• Q: What is the difference between if-else and switch?

• Q: What is fall-through in switch? Is it ever useful?

• Q: Why should you use .equals() instead of == for Strings?

14. Summary #

15. Next Chapter Recommendation #