Conditional Statements: Branch Your Program Logic

Introduction

This chapter covers conditional statements in Java—ways to run different code based on conditions. You will use if / else, the ternary operator, and switch. These build on Operators and prepare you for Loops and practice games later.

Prerequisites

• Variables, Operators, Strings
• Understanding of boolean expressions (true / false)

What Is a Conditional

A conditional chooses which block of code runs.

Metaphor: a railway switch—depending on the signal (condition), the train takes track A or track B.

int age = 20;
if (age >= 18) {
    System.out.println("Access granted");
} else {
    System.out.println("Access denied");
}

1) if and else

int score = 85;
 
if (score >= 90) {
    System.out.println("Excellent");
} else if (score >= 80) {
    System.out.println("Good");
} else if (score >= 60) {
    System.out.println("Pass");
} else {
    System.out.println("Need improvement");
}

Notes:

• Conditions must be boolean expressions
• Braces { } are required for multi-line blocks (single-line without braces is legal but discouraged for beginners)
• Java uses else if (two words), not elif

2) Ternary Operator (? :)

Compact form for simple either/or values:

int age = 17;
String label = (age >= 18) ? "Adult" : "Minor";
System.out.println(label);

Structure: (condition) ? valueIfTrue : valueIfFalse

Use when both branches are simple expressions. For long logic, prefer if / else for readability.

3) switch Statements

switch selects among multiple cases—often cleaner than long else if chains when comparing one value.

Classic switch (with break)

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;
    default:
        System.out.println("Other day");
        break;
}

break stops fall-through to the next case. Without break, execution “falls through” subsequent cases—sometimes intentional, usually a bug for beginners.

switch on String (Java 7+)

String command = "start";
 
switch (command) {
    case "start":
        System.out.println("Starting...");
        break;
    case "stop":
        System.out.println("Stopping...");
        break;
    default:
        System.out.println("Unknown command");
        break;
}

Modern switch expression (Java 14+, idiomatic on 21)

Arrow syntax avoids many break mistakes and can return a value:

String dayLabel = switch (day) {
    case 1 -> "Monday";
    case 2 -> "Tuesday";
    case 3 -> "Wednesday";
    default -> "Other day";
};
System.out.println(dayLabel);

Multiple labels per branch:

String type = switch (day) {
    case 1, 2, 3, 4, 5 -> "Weekday";
    case 6, 7 -> "Weekend";
    default -> "Invalid";
};

4) Combining Conditions

Use logical operators from Operators:

int age = 20;
boolean hasTicket = true;
 
if (age >= 18 && hasTicket) {
    System.out.println("Enter");
} else if (age < 18) {
    System.out.println("Too young");
} else {
    System.out.println("Need a ticket");
}

5) Real Mini Example: Login Gate

import java.util.Scanner;
 
public class LoginGate {
    public static void main(String[] args) {
        try (Scanner scanner = new Scanner(System.in)) {
            System.out.print("Username: ");
            String username = scanner.nextLine().strip();
 
            System.out.print("Password: ");
            String password = scanner.nextLine();
 
            if (username.isEmpty() || password.isEmpty()) {
                System.out.println("Username and password are required.");
            } else if ("admin".equals(username) && "java123".equals(password)) {
                System.out.println("Welcome, admin!");
            } else {
                System.out.println("Invalid credentials.");
            }
        }
    }
}

Common Beginner Mistakes

Mistake 1: Using = Instead of ==

// if (score = 90)  // compile error in Java — good safety net
if (score == 90) { }

Mistake 2: Comparing Strings with ==

if ("yes".equals(userInput)) { }  // correct for content

Mistake 3: Missing break in Classic switch

Causes unintended fall-through. Use arrow switch or add break deliberately.

Mistake 4: Ternary Overuse

Nested ternaries become unreadable. Prefer if / else for complex logic.

Mini Practice

Write a program that reads an integer hour (0–23) and prints:

• Good morning for 5–11
• Good afternoon for 12–17
• Good evening for 18–21
• Good night otherwise

Try both if / else and switch versions.

What’s Next

Repeat actions with Loop Statements, then store sequences in Arrays.

FAQ

When should I use switch instead of if / else?

When one expression maps to many discrete values (int, enum, String). For ranged checks (score ranges), if / else is often clearer.

Does switch work with double?

No. switch supports byte, short, char, int, Byte, Short, Character, Integer, enum, and String (and related patterns in newer Java).

What is fall-through?

When a case runs without break, execution continues into the next case. Arrow syntax (->) avoids fall-through by default.

Can I nest if statements?

Yes. Keep nesting shallow for readability—early return (in methods) or combined conditions often help.

How does the ternary operator relate to if / else?

It is an expression that picks one of two values. if / else is a statement for broader side effects (println, loops, etc.).