Java Reference
In-Depth Information
two values:
true
or
false
. For example, the following statement assigns
true
to the
variable
lightsOn
:
boolean
lightsOn =
true
;
true
and
false
are literals, just like a number such as
10
. They are treated as reserved words
and cannot be used as identifiers in the 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 1
Boolean literals
7?,” 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.current-
TimeMillis() / 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
.
+
VideoNote
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
int
number1 = (
int
)(System.currentTimeMillis() %
10
);
generate
number1
generate
number2
6
int
number2 = (
int
)(System.currentTimeMillis() /
7
%
10
);
7
8
// Create a Scanner
9 Scanner input =
new
Scanner(System.in);
10
11 System.out.print(
12
show question
"What is "
+ number1 +
" + "
+ number2 +
"? "
);
13
14
int
number = input.nextInt();
15
16 System.out.println(
17 number1 +
" + "
+ number2 +
" = "
+ answer +
" is "
+
18 (number1 + number2 == answer));
19 }
20 }
display result
What is 1 + 7? 8
1 + 7 = 8 is true
What is 4 + 8? 9
4 + 8 = 9 is false
line#
number1
number2
answer
output
5
4
6
8
14
9
16
4 + 8 = 9 is false
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