Java Lesson — Boolean, Relational Operators, and Logical Operators

What is a boolean?

A boolean in Java is a data type that stores only one of two possible values: true or false.

boolean isJavaFun = true;
boolean isFishFlying = false;

System.out.println(isJavaFun);
System.out.println(isFishFlying);

Boolean values are very useful when you want to test a condition, such as whether a student passed, whether a number is even, or whether a user is allowed to log in.

Relational Operators

Relational operators compare two values and produce a boolean result. That means the answer will always be either true or false.

Examples

int a = 10;
int b = 20;

System.out.println(a == b); // false
System.out.println(a != b); // true
System.out.println(a < b);  // true
System.out.println(a > b);  // false
System.out.println(a <= 10); // true
System.out.println(b >= 15); // true

These operators do not change the values. They only compare them and return a boolean result.

Logical Operators

Logical operators are used when you want to combine two or more boolean conditions, or when you want to reverse a condition.

How AND works

The && operator returns true only when both conditions are true.

int age = 20;
boolean hasIdCard = true;

System.out.println(age >= 18 && hasIdCard); // true

How OR works

The || operator returns true if at least one condition is true.

boolean isHoliday = false;
boolean isSunday = true;

System.out.println(isHoliday || isSunday); // true

How NOT works

The ! operator reverses the boolean value. It changes true to false and false to true.

boolean isRaining = false;

System.out.println(!isRaining); // true

Using booleans and operators in if statements

These operators become very useful when you write decision-making code.

int marks = 75;

if (marks >= 40) {
    System.out.println("Pass");
} else {
    System.out.println("Fail");
}

int age = 22;
boolean hasTicket = true;

if (age >= 18 && hasTicket) {
    System.out.println("You may enter.");
} else {
    System.out.println("Entry not allowed.");
}

Important beginner note: = versus ==

Many beginners confuse = and ==.

• = means assignment. It stores a value in a variable.
• == means comparison. It checks whether two values are equal.

int x = 5;      // assignment
System.out.println(x == 5); // comparison, result is true

This difference is extremely important in Java programming.

Complete example

public class Main {
    public static void main(String[] args) {
        int age = 19;
        int marks = 68;
        boolean hasAdmitCard = true;

        System.out.println("age >= 18: " + (age >= 18));
        System.out.println("marks >= 40: " + (marks >= 40));
        System.out.println("hasAdmitCard: " + hasAdmitCard);

        if (marks >= 40 && hasAdmitCard) {
            System.out.println("Student can appear in the next step.");
        } else {
            System.out.println("Student cannot appear in the next step.");
        }

        if (age < 18 || marks > 60) {
            System.out.println("At least one special condition is true.");
        }

        System.out.println("Not having admit card: " + !hasAdmitCard);
    }
}

Assignments

Interactive MCQ Quiz

Choose one answer for each question and click Check Answers.

Quick revision

• A boolean stores only true or false.
• Relational operators compare values and return boolean results.
• == checks equality, while = assigns a value.
• && means both conditions must be true.
• || means at least one condition must be true.
• ! reverses a boolean value.
• These operators are heavily used in if statements and loops.