So far we have only seen three types of variables:

int

integers, hold numbers (positive or negative) with no fractional parts

double

“double-precision floating-point” numbers (positive or negative) that could have a fractional part

String

a string of characters, hold words, phrases, symbols, sentences, whatever

But as a wise man once said, “There is anotherâ€¦.” A “Boolean” variable
(named after the mathematician George Boole) cannot hold numbers or words. It
can only store one of two values: true or false. That’s it. We can
use them to perform logic. To the code!

What You Should See

On line 14 the Boolean variable a is set equal to something strange: the
result of a comparison. The current value in the variable x is compared to
the value of the variable y. If x’s value is less than y’s, then the
comparison is true and the Boolean value true is stored into a. If x
is not less than y, then the comparison is false and the Boolean value
false is stored into a. (I think that is easier to understand than
it is to write.)

Line 15 is similar, except that the comparison is “less than or equal to”,
and the Boolean result is stored into b.

Line 16 is “equal to”: c will be set to the value true if x holds
the same value as y. The comparison in line 17 is “not equal to”. Lines
18 and 19 are “greater than” and “greater than or equal to”, respectively.

On lines 21 through 26, we display the values of all those Boolean variables on
the screen.

Line 29 through line 34 introduce the “not” operator, which is an
exclamation point (!). It takes the logical opposite. So on line
29 we display the logical negation of “x is less than y?”, and we
also print out the truth value of “x is greater than or equal to y?”,
which are equivalent. (The opposite of “less than” is “greater than
or equal to”.) Lines 30 through 34 show the opposites of the remaining
relational operators.