1-The most easy way to understand if, if else and nested if statements.

🔀 Control Statements in Java: if, if-else and Nested if

📌 Introduction

Control statements in Java are used to control the flow of execution of a program. By default, Java executes statements sequentially, but real-world programs require decision-making based on conditions.

The if, if-else, and nested if statements allow a program to choose different execution paths depending on whether a condition is true or false.

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🧠 What Are Control Statements?

📌 Definition

Control statements are statements that alter the normal flow of execution based on conditions or decisions.

Java control statements are broadly classified into:

• Decision-making statements
• Looping statements
• Branching statements

👉 In this article, we focus on decision-making statements.

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✅ The if Statement in Java

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🔹 Syntax of if Statement

if (condition) {
    // statements to execute if condition is true
}

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🔹 How if Works

• The condition must be of boolean type
• If the condition is true, the block executes
• If false, the block is skipped

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🧪 Example: Simple if

int age = 20;

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

✔ Output:

Eligible to vote

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⚠️ Important Rule

The condition inside if must be boolean.

❌ Invalid:

if (age)   // compilation error

✔ Correct:

if (age > 0)

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❌ Common Mistakes with if

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❌ Mistake 1: Using Assignment Instead of Comparison

if (x = 5)   // ERROR

🧠 = is assignment, not comparison.

✔ Correct:

if (x == 5)

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❌ Mistake 2: Semicolon After if

if (x > 0); {
    System.out.println("Positive");
}

⚠️ This block executes always, regardless of condition.

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🔁 The if-else Statement in Java

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🔹 Syntax of if-else

if (condition) {
    // executes if condition is true
} else {
    // executes if condition is false
}

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🧪 Example: if-else

int number = 7;

if (number % 2 == 0) {
    System.out.println("Even number");
} else {
    System.out.println("Odd number");
}

✔ Output:

Odd number

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🧠 Flow Explanation

• Condition checked
• One and only one block executes
• Either if or else, never both

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⚠️ Tricky Example: Braces Matter

int x = 10;

if (x > 5)
    System.out.println("Greater than 5");
    System.out.println("End");

✔ Output:

Greater than 5
End

🧠 Only the first statement belongs to if.

✔ Best practice:

if (x > 5) {
    System.out.println("Greater than 5");
}

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🔂 Nested if Statement in Java

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🔹 What Is Nested if?

An if inside another if is called a nested if.
It is used when decisions depend on multiple conditions.

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🔹 Syntax

if (condition1) {
    if (condition2) {
        // statements
    }
}

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🧪 Example: Nested if

int marks = 85;

if (marks >= 35) {
    if (marks >= 75) {
        System.out.println("Distinction");
    }
}

✔ Output:

Distinction

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🧠 Explanation

• First condition checks pass/fail
• Second condition checks grade
• Inner if executes only if outer if is true

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⚠️ The “Dangling else” Problem (VERY IMPORTANT)

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🔥 Confusing Code

int x = 10;

if (x > 5)
    if (x > 8)
        System.out.println("A");
    else
        System.out.println("B");

✔ Output:

A

🧠 else is associated with the nearest if, not the first one.

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✔ Correct Version (Using Braces)

if (x > 5) {
    if (x > 8) {
        System.out.println("A");
    } else {
        System.out.println("B");
    }
}

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⚠️ Common Compilation Errors

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❌ Using Non-Boolean Conditions

if (5)   // ERROR

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❌ Missing Parentheses

if x > 5   // ERROR

✔ Correct:

if (x > 5)

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❌ Missing Braces in Nested Logic

Leads to logical errors, not compilation errors.

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🧠 Best Practices for Control Statements

✔ Always Use Braces

Even for single statements.

✔ Keep Conditions Simple

Complex conditions reduce readability.

✔ Avoid Deep Nesting

Too many nested if statements make code hard to maintain.

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📘 Real-World Examples

• Login validation
• Exam grading systems
• Eligibility checks
• Decision-based workflows

Example:

if (username.equals("admin")) {
    if (password.equals("1234")) {
        System.out.println("Login successful");
    }
}

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📌 Quick Summary

• if → executes block when condition is true
• if-else → chooses between two paths
• Nested if → handles multiple dependent conditions
• Conditions must be boolean
• Braces prevent logical errors

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🏁 Conclusion

Control statements form the foundation of decision-making in Java programs. Mastering if, if-else, and nested if helps in writing logical, readable, and error-free programs. Understanding common mistakes and tricky cases ensures better debugging skills and confidence in problem-solving.