Conditional Statements

1. Overview & Types

Conditional statements control program flow by executing different code blocks based on conditions.

If Statement

Execute code when condition is true

if (condition) { }

Switch Statement

Multiple conditions with single variable

switch (variable) { }

Ternary Operator

Shorthand for simple if-else

condition ? value1 : value2

Decision Flow

Condition (Evaluate Expression) → Decision (True or False?) → Action (Execute Code Block)

2. If Statements

Simple If

int age = 18;
if (age >= 18) {
    System.out.println("You can vote!");
}

If-Else

int score = 85;
if (score >= 90) {
    System.out.println("Grade A");
} else {
    System.out.println("Grade B or below");
}

If-Else If-Else

int score = 85;
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 {
    System.out.println("Grade F");
}

Comparison Conditions

age > 18

score == 100

name != null

price <= 50.0

Logical Conditions

age >= 18 && hasLicense

day == “Saturday” || day == “Sunday”

!isExpired

(x > 0) && (x < 100)

Nested If Statements

boolean isRaining = true;
int temperature = 25;

if (isRaining) {
    if (temperature 15) {
        System.out.println("Wear a raincoat and jacket");
    } else {
        System.out.println("Just carry an umbrella");
    }
} else {
    if (temperature > 30) {
        System.out.println("Wear light clothes");
    } else {
        System.out.println("Normal clothes are fine");
    }
}

3. Switch Statements

Switch statements provide a clean way to handle multiple conditions on a single variable.

Traditional Switch

int dayOfWeek = 3;
switch (dayOfWeek) {
    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");
}

Switch Expression (Java 14+)

String dayName = switch (dayOfWeek) {
    case 1 -> "Monday";
    case 2 -> "Tuesday";
    case 3 -> "Wednesday";
    case 4 -> "Thursday";
    case 5 -> "Friday";
    default -> "Weekend";
};

Multiple Cases & String Switch

switch (grade) {
    case 'A':
    case 'B':
        System.out.println("Good work!");
        break;
    case 'C':
        System.out.println("Average");
        break;
    default:
        System.out.println("Needs improvement");
}

Important Notes

• Break statements: Prevent fall-through to next case
• Default case: Always include for unmatched values
• Supported types: byte, short, int, char, String, enum

4. Ternary Operator

The ternary operator provides a concise way to write simple if-else statements in one line.

Syntax

condition ? valueIfTrue : valueIfFalse

Before and After Comparison

// Before (If-Else)
int age = 20;
String status;
if (age >= 18) {
    status = "Adult";
} else {
    status = "Minor";
}

// After (Ternary) - Much cleaner!
int age = 20;
String status = (age >= 18) ? "Adult" : "Minor";

Common Use Cases

• Variable Assignment: int max = (a > b) ? a : b;
• Method Parameters: println(score > 90 ? "Pass" : "Fail");
• Return Values: return (count == 0) ? "Empty" : "Has items";
• Null Safety: String name = (user != null) ? user.getName() : "Guest";

Nested Ternary (Use Sparingly)

// Grade calculation using nested ternary
int score = 85;
String grade = (score >= 90) ? "A" :
               (score >= 80) ? "B" :
               (score >= 70) ? "C" : "F";

// Better approach for complex conditions - use if-else
String grade;
if (score >= 90) grade = "A";
else if (score >= 80) grade = "B";
else if (score >= 70) grade = "C";
else grade = "F";

5. Practical Examples

User Authentication

String username = "admin";
String password = "123456";

if (username.equals("admin") && password.equals("123456")) {
    System.out.println("Login successful");
} else {
    System.out.println("Invalid credentials");
}

Calculator App

double a = 10, b = 5;
String operator = "+";

double result = switch (operator) {
    case "+" -> a + b;
    case "-" -> a - b;
    case "*" -> a * b;
    case "/" -> (b != 0) ? a / b : 0;
    default -> 0;
};

Payment Processing

double amount = 150.0;
double balance = 200.0;
boolean isVip = true;

if (amount double discount = isVip ? 0.1 : 0.05;
    double finalAmount = amount * (1 - discount);
    System.out.println("Payment approved: $" + finalAmount);
} else {
    System.out.println("Insufficient funds");
}

6. Best Practices

Good Practices

• Use meaningful boolean variable names
• Keep conditions simple and readable
• Always include default case in switch
• Use ternary for simple assignments
• Avoid deep nesting (max 2-3 levels)
• Use parentheses for complex conditions

Avoid These

• Complex nested ternary operators
• Missing break statements in switch
• Magic numbers in conditions
• Deep nesting (arrow anti-pattern)
• Comparing booleans with == true
• Long switch statements

Clean Code Example

// ❌ Hard to Read
if (user.getAge() >= 18 && user.getAge() 65 && user.isActive() == true && user.getBalance() > 1000) {
    processPayment();
}

// ✅ Easy to Read
boolean isEligibleAge = user.getAge() >= 18 && user.getAge() 65;
boolean hasValidAccount = user.isActive() && user.getBalance() > 1000;

if (isEligibleAge && hasValidAccount) {
    processPayment();
}

Performance Tips

• Short-Circuit Evaluation: Place simpler conditions first in logical operators
• Switch vs If-Else: Use switch for 3+ discrete values, if-else for ranges
• Early Return: Return early to reduce nesting levels

What’s Next?

• Learn Loops (for, while, do-while)
• Master Arrays and Collections
• Explore Object-Oriented Programming
• Practice Exception Handling