Programming Tutorials

how to use boolean data type in Java

By: Lakshmi in Java Tutorials on 2007-09-07  

Java has a simple type, called boolean, for logical values. It can have only one of two possible values, true or false. This is the type returned by all relational operators, such as a < b. boolean is also the type required by the conditional expressions that govern the control statements such as if and for.

Here is a program that demonstrates the boolean type:

// Demonstrate boolean values.
class BoolTest {
    public static void main(String args[]) {
        boolean b;
        b = false;
        System.out.println("b is " + b);
        b = true;
        System.out.println("b is " + b);
        // a boolean value can control the if statement
        if (b)
            System.out.println("This is executed.");
        b = false;
        if (b)
            System.out.println("This is not executed.");
        // outcome of a relational operator is a boolean value
        System.out.println("10 > 9 is " + (10 > 9));
    }
}

The output generated by this program is shown here:

b is false
b is true
This is executed.
10 > 9 is true

There are three interesting things to notice about this program. First, as you can see, when a boolean value is output by println(), "true" or "false" is displayed. Second, the value of a boolean variable is sufficient, by itself, to control the if statement. There is no need to write an if statement like this:

if(b == true) ...

Third, the outcome of a relational operator, such as <, is a boolean value. This is why the expression 10 > 9 displays the value "true." Further, the extra set of parentheses around 10 > 9 is necessary because the + operator has a higher precedence than the >.