Lesson 9 of 20

Conditional Statements

Make decisions with if, else if, else, and switch.

Learning objectives

• Write an if statement from a Boolean condition.
• Use else if for multiple ranges or alternatives.
• Use switch when selecting among discrete values.
• Avoid overlapping or unreachable conditions.
• Build a grade classification program.

1. if statements

An if block runs only when its condition evaluates to true.

Example: pass or fail

int mark = 68;

if (mark >= 50) {
    System.out.println("Pass");
}

2. if-else

Use else when exactly one of two branches should run.

int mark = 42;

if (mark >= 50) {
    System.out.println("Pass");
} else {
    System.out.println("Fail");
}

3. else-if chains

Order matters. Check the highest range first so a high score is not captured by a lower condition.

Example: grade classification

int mark = 83;

if (mark >= 80) {
    System.out.println("Grade A");
} else if (mark >= 70) {
    System.out.println("Grade B");
} else if (mark >= 60) {
    System.out.println("Grade C");
} else if (mark >= 50) {
    System.out.println("Grade D");
} else {
    System.out.println("Grade F");
}

4. switch

switch is useful when a single value selects among known alternatives.

int menuChoice = 2;

switch (menuChoice) {
    case 1 -> System.out.println("Add record");
    case 2 -> System.out.println("Search record");
    case 3 -> System.out.println("Exit");
    default -> System.out.println("Invalid choice");
}

Mini project: shipping charge calculator

public class ShippingCalculator {
    public static void main(String[] args) {
        double orderTotal = 135.00;
        boolean member = true;

        double shipping;

        if (orderTotal >= 150) {
            shipping = 0;
        } else if (member && orderTotal >= 100) {
            shipping = 5;
        } else {
            shipping = 12;
        }

        System.out.printf("Order: RM %.2f%n", orderTotal);
        System.out.printf("Shipping: RM %.2f%n", shipping);
        System.out.printf("Final total: RM %.2f%n", orderTotal + shipping);
    }
}

Common mistakes

Summary

Conditional statements make a program respond differently to different data. Lesson 10 introduces loops so the same logic can be repeated efficiently.