Java boolean Keyword
Usage and Examples

boolean Keyword in Java

In Java, boolean is a primitive data type that can hold only one of two possible values: true or false. These values are commonly used to control the flow of a program, particularly in conditional statements like if, while, and for.

Declaring a boolean Variable

To declare a boolean variable in Java, use the boolean keyword followed by the variable name and assign it either true or false.

public class BooleanExample {
    public static void main(String[] args) {
        boolean isJavaFun = true;
        boolean isSkyGreen = false;

        System.out.println("Is Java fun? " + isJavaFun);
        System.out.println("Is the sky green? " + isSkyGreen);
    }
}

Is Java fun? true
Is the sky green? false

Using boolean in Conditions

Boolean variables shine in control statements. Let's use them in an if condition to make decisions based on their value.

public class LoginCheck {
    public static void main(String[] args) {
        boolean isLoggedIn = true;

        if (isLoggedIn) {
            System.out.println("Welcome back, user!");
        } else {
            System.out.println("Please log in first.");
        }
    }
}

Welcome back, user!

Boolean Expressions

Often, booleans are not explicitly assigned. Instead, they result from expressions such as comparisons or logical operations.

public class BooleanExpressions {
    public static void main(String[] args) {
        int age = 20;
        boolean canVote = age >= 18;

        System.out.println("Eligible to vote? " + canVote);
    }
}

Eligible to vote? true

Logical Operators with booleans

Boolean values can be combined using logical operators like && (AND), || (OR), and ! (NOT).

public class BooleanLogic {
    public static void main(String[] args) {
        boolean hasID = true;
        boolean isAdult = false;

        boolean canEnter = hasID && isAdult;
        System.out.println("Can enter the club? " + canEnter);
    }
}

Can enter the club? false

Default Value of boolean

When declared as a class field but not initialized, a boolean defaults to false.

public class DefaultBoolean {
    static boolean isAvailable;

    public static void main(String[] args) {
        System.out.println("Is available? " + isAvailable);
    }
}

Is available? false

Common Use Cases of boolean in Java

• Controlling flow with if, else, while, for
• Returning status from methods (e.g., isEmpty(), equals())
• Logical checks in authentication, input validation, and more

Method Returning boolean

Many Java methods return a boolean to indicate success or failure or to answer a yes/no question.

public class EvenCheck {
    public static boolean isEven(int number) {
        return number % 2 == 0;
    }

    public static void main(String[] args) {
        int num = 5;
        System.out.println("Is " + num + " even? " + isEven(num));
    }
}

Is 5 even? false