Java Reference
In-Depth Information
A variable that holds a Boolean value is known as a
Boolean variable
. The
boolean
data
type is used to declare Boolean variables. A
boolean
variable can hold one of the two values:
true
or
false
. For example, the following statement assigns
true
to the variable
lightsOn
:
Boolean variable
boolean
lightsOn =
true
;
true
and
false
are literals, just like a number such as
10
. They are reserved words and
cannot be used as identifiers in your program.
Suppose you want to develop a program to let a first-grader practice addition. The program
randomly generates two single-digit integers,
number1
and
number2
, and displays to the student
a question such as “What is ”, as shown in the sample run in Listing 3.1. After the student
types the answer, the program displays a message to indicate whether it is true or false.
There are several ways to generate random numbers. For now, generate the first
integer using
System.currentTimeMillis() % 10
and the second using
System.currentTimeMillis() / 7 % 10
. Listing 3.1 gives the program. Lines 5-6
generate two numbers,
number1
and
number2
. Line 14 obtains an answer from the user. The
answer is graded in line 18 using a Boolean expression
number1 + number2 == answer
.
Boolean literals
VideoNote
1
+
7?
Program addition quiz
L
ISTING
3.1
AdditionQuiz.java
1
import
java.util.Scanner;
2
3
public class
AdditionQuiz {
4
public static void
main(String[] args) {
5
6
7
8
// Create a Scanner
9 Scanner input =
new
Scanner(System.in);
10
11 System.out.print(
12
int
number1 = (
int
)(System.currentTimeMillis() %
10
);
generate number1
generate number2
int
number2 = (
int
)(System.currentTimeMillis() /
7
%
10
);
show question
"What is "
+ number1 +
" + "
+ number2 +
"? "
);
13
14
15
16 System.out.println(
17 number1 +
" + "
+ number2 +
" = "
+ answer +
" is "
+
18 (
int
answer = input.nextInt();
display result
number1 + number2 == answer
));
19 }
20 }
What is 1 + 7?
1 + 7 = 8 is true
8
What is 4 + 8?
4 + 8 = 9 is false
9
line#
number1
number2
answer
output
5
4
6
8
14
9
16
4 + 8 = 9 is false
