Part 1: `if-else` Statement

Selection statements allow a Java program to choose which block of code to execute based on a condition.

Think of them as decision-makers. Just like we make decisions in daily life—"If it is raining, take an umbrella; otherwise, go without one."—Java uses selection statements to make decisions during program execution.

Java provides two selection statements:

• if-else
• switch

In this article, we'll focus on the if-else statement.

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What Is the if Statement?

The if statement executes a block of code only when a specified condition evaluates to true.

Syntax

if (condition) {
    // Executes when the condition is true
}

If the condition is false, the block is skipped.

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Your First if Program

int age = 20;

if (age >= 18) {
    System.out.println("Eligible to vote");
}

Output

Eligible to vote

Since the condition is true, the statement inside the if block executes.

---

Now change the value.

int age = 15;

if (age >= 18) {
    System.out.println("Eligible to vote");
}

Output

No Output

The condition is false, so Java skips the block.

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What Is the if-else Statement?

The if-else statement provides an alternative block of code when the condition is false.

Syntax

if (condition) {
    // Executes when the condition is true
} else {
    // Executes when the condition is false
}

Exactly one block is executed.

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Example

int marks = 45;

if (marks >= 35) {
    System.out.println("Pass");
} else {
    System.out.println("Fail");
}

Output

Pass

Now change the marks.

int marks = 20;

if (marks >= 35) {
    System.out.println("Pass");
} else {
    System.out.println("Fail");
}

Output

Fail

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Nested if Statements

An if statement can contain another if statement.

This is called a nested if.

Example

int age = 25;
boolean hasLicense = true;

if (age >= 18) {

    if (hasLicense) {
        System.out.println("Can drive");
    }

}

Output

Can drive

Nested if statements are useful when multiple conditions must be satisfied.

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Rule 1: The Condition Must Be boolean

This is one of the biggest differences between Java and languages like C or C++.

In Java, the condition inside an if statement must evaluate to a boolean value.

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Valid Example

int age = 25;

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

The expression

age > 18

returns a boolean (true or false).

---

Invalid Example

int age = 25;

if (age) {
    System.out.println("Adult");
}

Compile-time error

incompatible types:
int cannot be converted to boolean

Why?

Java does not automatically convert numbers into boolean values.

Unlike C or C++:

• 0 is not treated as false.
• Non-zero values are not treated as true.

Java requires an explicit boolean expression.

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Rule 2: = vs == — The Classic Interview Trap

Many beginners accidentally use the assignment operator (=) instead of the equality operator (==).

Let's understand the difference.

---

Assignment (=)

boolean passed = false;

if (passed = true) {

    System.out.println("Passed");

}

Output

Passed

Why?

The assignment

passed = true

stores true in the variable.

The assignment expression itself evaluates to true.

So the if condition becomes

if (true)

which always executes.

---

Equality (==)

boolean passed = false;

if (passed == true) {

    System.out.println("Passed");

}

Output

No Output

Here, Java compares the value instead of assigning it.

---

Why Doesn't This Work?

int number = 10;

if (number = 20) {

}

Compile-time error

incompatible types:
int cannot be converted to boolean

The assignment returns an int, but if expects a boolean expression.

---

Interview Tip

Whenever you write an if condition, always double-check whether you intended to use

• =
• or ==

This mistake appears frequently in coding interviews.

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Rule 3: Curly Braces ({}) Are Optional

If the body contains only one statement, curly braces may be omitted.

Example

if (true)
    System.out.println("Hello");

This is perfectly valid.

---

The same program with braces.

if (true) {
    System.out.println("Hello");
}

Both versions produce

Hello

---

Multiple Statements Require Braces

Incorrect

if (true)
    System.out.println("Hello");
    System.out.println("Rajesh");

Output

Hello
Rajesh

Only the first statement belongs to the if.

The second statement executes unconditionally.

---

Correct

if (true) {

    System.out.println("Hello");

    System.out.println("Rajesh");

}

Now both statements belong to the if block.

---

Variable Declarations Need Braces

Incorrect

if (true)

    int age = 25;

Compile-time error

variable declaration not allowed here

A variable declaration cannot be the only statement controlled by an if without braces.

Correct

if (true) {

    int age = 25;

    System.out.println(age);

}

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Rule 4: A Semicolon (;) Is a Valid Empty Statement

Many beginners accidentally write

if (true);

System.out.println("Hello");

Output

Hello

What Happened?

The semicolon acts as an empty statement.

The if controls only the empty statement.

if (true)
    ;

The println() statement is completely independent.

This is a very common programming mistake.

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Common Beginner Mistakes

Forgetting Braces

Incorrect

if (marks >= 35)

    System.out.println("Pass");

    System.out.println("Congratulations!");

Many beginners expect both lines to execute only when the condition is true.

Only the first line belongs to the if.

---

Using = Instead of ==

Incorrect

if (passed = true)

Correct

if (passed == true)

or simply

if (passed)

---

Passing an Integer Instead of a Boolean

Incorrect

int number = 1;

if (number)

Correct

if (number != 0)

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Accidentally Adding a Semicolon

Incorrect

if (marks >= 35);

System.out.println("Pass");

The condition has no effect because of the extra semicolon.

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Best Practices

• Always use meaningful variable names such as age, marks, or isEligible.
• Use braces even for a single statement to improve readability.
• Avoid writing complex conditions inside an if.
• Use descriptive boolean variables like isLoggedIn or hasLicense.
• Carefully distinguish between = and ==.
• Never accidentally place a semicolon immediately after an if.

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Quick Memory Trick 🧠

Think of the if statement as asking a simple question:

"Is the condition true?"

If the answer is Yes, Java executes the if block.

Otherwise, it executes the else block (if present).

Remember:

• Condition → Must be boolean
• One statement → Braces optional
• Multiple statements → Braces required
• = assigns a value
• == compares values

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Key Takeaways

• The if statement executes code only when its condition is true.
• The if-else statement chooses between two blocks of code.
• The condition must always evaluate to a boolean value.
• Java does not automatically convert numbers into booleans.
• = performs assignment, while == performs comparison.
• Curly braces are optional for a single statement but recommended.
• A semicolon (;) is a valid empty statement and can introduce subtle bugs.
• Nested if statements allow multiple conditions to be checked.

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Happy Coding!