Chapter: Java The Complete Reference - The Java Language - Data Types, Variables, and Arrays

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Booleans

Java has a primitive type, called boolean, for logical values. It can have only one of two possible values, true or false.

Booleans

 

Java has a primitive 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, as in the case of 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 >.

 

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