Booleans in java

Java has a simple type, called Boolean, for logical values. It can have only one of two possible values, true of 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);
  if ( b ) 
   System.out.println("This is not executed. ");
  System.out.println("10 > 9 is " + (10 > 9) );
  }
}

The output generated by this program is shown here:

b is false
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 >.