Conditional Statements in Java: ICSE Class 9 Notes on if, if-else and switch

A program often has to make decisions: is the number even, has the student passed, which slab does the electricity bill fall in? Conditional statements let a Java program choose what to do based on a condition. This chapter is the base of almost every program you will write in ICSE Class 9 and 10.

1. The if statement

The if statement runs a block only when the condition is true.

if (marks >= 40) {
    System.out.println("Pass");
}

2. The if-else statement

The if-else statement chooses between two paths.

if (n % 2 == 0)
    System.out.println(n + " is even");
else
    System.out.println(n + " is odd");

3. The if-else-if ladder

Use an if-else-if ladder for several conditions checked in order. The first true condition wins, and the rest are skipped.

if (percent >= 90)
    grade = 'A';
else if (percent >= 75)
    grade = 'B';
else if (percent >= 60)
    grade = 'C';
else
    grade = 'D';

The order matters. If you test percent >= 60 first, a student with 95 would get grade C.

4. Nested if

A nested if is an if placed inside another if. Use it when one decision depends on another.

if (a > b) {
    if (a > c)
        System.out.println("Largest: " + a);
    else
        System.out.println("Largest: " + c);
} else {
    if (b > c)
        System.out.println("Largest: " + b);
    else
        System.out.println("Largest: " + c);
}

5. The ternary operator

The ternary operator is a one-line if-else that returns a value:

int max = (a > b) ? a : b;
String result = (marks >= 40) ? "Pass" : "Fail";

6. The switch statement

switch compares one variable against several fixed values (cases). It works with int, char, String and some other types, but not with double, float, long or boolean.

switch (day) {
    case 1:
        System.out.println("Monday");
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    default:
        System.out.println("Invalid day");
}

• break ends the switch. Without break, execution "falls through" into the next case.
• default runs when no case matches. It is optional.

Fall-through: an output question

int x = 2;
switch (x) {
    case 1: System.out.print("One ");
    case 2: System.out.print("Two ");
    case 3: System.out.print("Three ");
    default: System.out.print("Other");
}

Output: Two Three Other. There are no break statements, so once case 2 matches, every following statement runs.

if-else vs switch

• What it tests: if-else can test any boolean condition, including ranges like x > 10; switch tests one variable against exact values.
• Data types: if-else works with every type; switch does not work with double, float, long or boolean.
• Best for: if-else suits ranges and complex conditions; switch suits menus and fixed choices.

Solved program: menu-driven calculator

import java.util.Scanner;

class Calculator {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter two numbers: ");
        double a = sc.nextDouble(), b = sc.nextDouble();
        System.out.print("Enter operator (+ - * /): ");
        char op = sc.next().charAt(0);

        switch (op) {
            case '+': System.out.println("Result = " + (a + b)); break;
            case '-': System.out.println("Result = " + (a - b)); break;
            case '*': System.out.println("Result = " + (a * b)); break;
            case '/':
                if (b != 0)
                    System.out.println("Result = " + (a / b));
                else
                    System.out.println("Division by zero is not allowed");
                break;
            default:
                System.out.println("Invalid operator");
        }
    }
}

The program combines a switch (to choose the operation) with an if-else inside one case (to prevent division by zero).

Practice questions

1. Write a program to check whether a year is a leap year. *Hint: divisible by 4 and not by 100, or divisible by 400.*
2. Give the output: int a = 5; if (a > 3) if (a > 10) System.out.print("X"); else System.out.print("Y");
3. Why can't switch be used to check whether marks > 40?

Answers:

1. if ((y % 4 == 0 && y % 100 != 0) || y % 400 == 0) means it is a leap year.
2. Y. The else belongs to the nearest if, which is if (a > 10).
3. Because switch compares against exact values. It cannot test a range or relational condition.

Continue with Loops in Java and practise with our ICSE Class 9 Computer Applications Sample Paper.