JAVA

Conditional Statements

Most programs need to make decisions. A login system must check whether a username and password are correct. A banking application must verify that an account has sufficient balance before allowing a withdrawal. A student management system may assign grades based on marks.

To perform these tasks, Java uses conditional statements. A conditional statement evaluates a condition and executes different blocks of code depending on whether that condition is true or false.

In this chapter, you will learn how to make decisions in Java using if, if-else, and else-if statements.

What is a Condition?

A condition is an expression that evaluates to either true or false.

Examples

age >= 18
marks > 90
balance < withdrawAmount

The result of each expression is either:

true
false

Conditional statements use these results to determine which block of code should execute.

The if Statement

The if statement executes a block of code only when a condition is true.

Syntax

if(condition) {
    // code to execute
}

Example

int age = 18;

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

Output

Eligible to vote

Since the condition age >= 18 evaluates to true, the code inside the if block is executed.

The if-else Statement

In many situations, there are two possible outcomes. If the condition is true, one block of code executes. If the condition is false, another block executes.

Syntax

if(condition) {
    // code if true
}
else {
    // code if false
}

Example

int age = 16;

if(age >= 18) {
    System.out.println("Eligible to vote");
}
else {
    System.out.println("Not eligible to vote");
}

Output

Not eligible to vote

Since the condition is false, Java skips the if block and executes the else block.

The else-if Statement

When multiple conditions need to be checked, use else-if.

Java evaluates conditions from top to bottom. As soon as one condition becomes true, the remaining conditions are skipped.

Example

int marks = 85;

if(marks >= 90) {
    System.out.println("Grade A");
}
else if(marks >= 80) {
    System.out.println("Grade B");
}
else if(marks >= 70) {
    System.out.println("Grade C");
}
else {
    System.out.println("Grade D");
}

Output

Grade B

Since 85 is greater than or equal to 80, the second condition becomes true and Java prints Grade B.

Comparison Operators

Conditions are usually created using comparison operators.

Example

int age = 20;
System.out.println(age >= 18);

Output

true

The expression evaluates to true because 20 is greater than 18.

Logical Operators

Logical operators allow multiple conditions to be combined into a single expression.

AND (&&)

Returns true only when both conditions are true.

Example

int age = 20;
boolean citizen = true;

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

Output

Eligible

OR (||)

Returns true if at least one condition is true.

Example

int marks = 95;

if(marks >= 90 || marks == 90) {
    System.out.println("Excellent");
}

Output

Excellent

NOT (!)

Reverses a boolean value.

Example

boolean isLoggedIn = false;

if(!isLoggedIn) {
    System.out.println("Please login");
}

Output

Please login

First Complete Program

Example

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        System.out.print("Enter your age: ");
        int age = sc.nextInt();

        if(age >= 18) {
            System.out.println("You are eligible to vote");
        }
        else {
            System.out.println("You are not eligible to vote");
        }
    }
}

Input

20

Output

You are eligible to vote

Explanation

• The program asks the user to enter an age.
• The entered value is stored in the variable age.
• Java checks whether the age is greater than or equal to 18.
• If the condition is true, one message is displayed.
• Otherwise, a different message is displayed.

Nested if Statements

An if statement can be placed inside another if statement.

This is known as a nested if.

Example

int age = 20;
boolean hasLicense = true;

if(age >= 18) {
    if(hasLicense) {
        System.out.println("You can drive");
    }
}

Output

You can drive

Both conditions must be true for the message to be displayed.

Common Mistakes

Using = Instead of ==

Wrong

if(age = 18)

Correct

if(age == 18)

Explanation

• = assigns a value.
• == compares two values.

Missing Braces

Wrong

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

Only the first statement belongs to the if.

Correct

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

Key Takeaways

• Conditional statements allow programs to make decisions.
• A condition always evaluates to true or false.
• if executes code when a condition is true.
• if-else provides two possible outcomes.
• else-if is used when multiple conditions need to be checked.
• Comparison operators create conditions.
• Logical operators combine multiple conditions.
• Conditional statements are one of the most important building blocks in Java programming.