Java If-Else — Conditional Statements Explained

Conditional statements let your program make decisions. The if-else statement is the most fundamental control structure in Java.

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The if Statement

Executes a block only if the condition is true.

int temperature = 35;

if (temperature > 30) {
    System.out.println("It's hot outside!");
}

Syntax:

if (condition) {
    // code to execute when condition is true
}

The condition must be a boolean expression.

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if-else

Provides an alternative when the condition is false.

int age = 16;

if (age >= 18) {
    System.out.println("You can vote.");
} else {
    System.out.println("You cannot vote yet.");
}

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else if — Multiple Conditions

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");
}
// Output: Grade: C

Java checks conditions top to bottom and executes the first matching block.

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Nested if

boolean hasTicket = true;
int age = 15;

if (hasTicket) {
    if (age >= 18) {
        System.out.println("Welcome to the movie.");
    } else {
        System.out.println("You need a guardian.");
    }
} else {
    System.out.println("Please buy a ticket.");
}

Tip: Avoid deep nesting (more than 2-3 levels). Refactor using early returns or separate methods.

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Single-Statement if (No Braces)

if (age >= 18)
    System.out.println("Adult");

This works, but always use braces {} — even for single statements:

// Dangerous — the second line ALWAYS runs
if (age >= 18)
    System.out.println("Adult");
    System.out.println("Can vote");  // NOT inside the if!

// Safe — intent is clear
if (age >= 18) {
    System.out.println("Adult");
    System.out.println("Can vote");
}

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Common Patterns

Guard Clauses (Early Return)

Instead of deep nesting, return early:

// Deep nesting — hard to read
public void processOrder(Order order) {
    if (order != null) {
        if (order.isValid()) {
            if (order.hasStock()) {
                // actual logic here
            }
        }
    }
}

// Guard clauses — flat and clear
public void processOrder(Order order) {
    if (order == null) return;
    if (!order.isValid()) return;
    if (!order.hasStock()) return;

    // actual logic here
}

Range Checking

public static String getAgeGroup(int age) {
    if (age < 0) return "Invalid";
    if (age < 13) return "Child";
    if (age < 18) return "Teenager";
    if (age < 65) return "Adult";
    return "Senior";
}

Null Checking

if (name != null && !name.isEmpty()) {
    System.out.println("Hello, " + name);
} else {
    System.out.println("Hello, stranger");
}

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The Ternary Operator (Recap)

A shorthand for simple if-else:

String status = (age >= 18) ? "Adult" : "Minor";

Use it only for simple, one-line decisions.

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Common Mistakes

1. Using = Instead of ==

// WRONG — assignment, not comparison
if (x = 5) { }  // compile error in Java

// CORRECT
if (x == 5) { }

2. Comparing Strings with ==

String input = scanner.nextLine();

// WRONG
if (input == "yes") { }

// CORRECT
if (input.equals("yes")) { }
// or
if ("yes".equals(input)) { }  // null-safe

3. Unnecessary Boolean Comparison

// Bad
if (isReady == true) { }

// Good
if (isReady) { }

4. Empty if Body

// Bug — the semicolon makes the if do nothing
if (x > 5);
{
    System.out.println("Greater");  // ALWAYS runs
}

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Quick Exercises

1. Write a program that reads a number and prints “Positive”, “Negative”, or “Zero”.
2. Write a program that determines if a year is a leap year.
3. Refactor this nested if into guard clauses:

   if (user != null) {
       if (user.isActive()) {
           if (user.hasPermission("admin")) {
               grantAccess();
           }
       }
   }
   

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Summary

Structure	When to Use
if	Single condition
if-else	Two alternatives
else if	Multiple conditions
Nested if	Conditions within conditions
Ternary ? :	Simple inline decisions
Guard clauses	Early exit to avoid nesting

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What’s Next?

When you have many specific values to check, if-else chains get long. That’s where switch comes in: Switch Statement.